draft-ietf-tsvwg-transport-encrypt-09.txt   draft-ietf-tsvwg-transport-encrypt-10.txt 
TSVWG G. Fairhurst TSVWG G. Fairhurst
Internet-Draft University of Aberdeen Internet-Draft University of Aberdeen
Intended status: Informational C. Perkins Intended status: Informational C. Perkins
Expires: May 6, 2020 University of Glasgow Expires: July 12, 2020 University of Glasgow
November 3, 2019 January 9, 2020
Considerations around Transport Header Confidentiality, Network Considerations around Transport Header Confidentiality, Network
Operations, and the Evolution of Internet Transport Protocols Operations, and the Evolution of Internet Transport Protocols
draft-ietf-tsvwg-transport-encrypt-09 draft-ietf-tsvwg-transport-encrypt-10
Abstract Abstract
To protect user data and privacy, Internet transport protocols have To protect user data and privacy, Internet transport protocols have
supported payload encryption and authentication for some time. Such supported payload encryption and authentication for some time. Such
encryption and authentication is now also starting to be applied to encryption and authentication is now also starting to be applied to
the transport protocol headers. This helps avoid transport protocol the transport protocol headers. This helps avoid transport protocol
ossification by middleboxes, while also protecting metadata about the ossification by middleboxes, while also protecting metadata about the
communication. Current operational practice in some networks inspect communication. Current operational practice in some networks inspect
transport header information within the network, but this is no transport header information within the network, but this is no
skipping to change at page 1, line 44 skipping to change at page 1, line 44
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This Internet-Draft will expire on May 6, 2020. This Internet-Draft will expire on July 12, 2020.
Copyright Notice Copyright Notice
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Context and Rationale . . . . . . . . . . . . . . . . . . . . 4 2. Context and Rationale . . . . . . . . . . . . . . . . . . . . 4
2.1. Use of Transport Header Information in the Network . . . 5 2.1. Use of Transport Header Information in the Network . . . 5
2.2. Authentication of Transport Header Information . . . . . 6 2.2. Authentication of Transport Header Information . . . . . 7
2.3. Observable Transport Header Fields . . . . . . . . . . . 7 2.3. Observable Transport Header Fields . . . . . . . . . . . 7
3. Current uses of Transport Headers within the Network . . . . 10 3. Current uses of Transport Headers within the Network . . . . 10
3.1. Observing Transport Information in the Network . . . . . 11 3.1. Observing Transport Information in the Network . . . . . 11
3.2. Transport Measurement . . . . . . . . . . . . . . . . . . 17 3.2. Transport Measurement . . . . . . . . . . . . . . . . . . 18
3.3. Use for Network Diagnostics and Troubleshooting . . . . . 21 3.3. Use for Network Diagnostics and Troubleshooting . . . . . 21
3.4. Header Compression . . . . . . . . . . . . . . . . . . . 22 3.4. Header Compression . . . . . . . . . . . . . . . . . . . 23
4. Encryption and Authentication of Transport Headers . . . . . 23 4. Encryption and Authentication of Transport Headers . . . . . 23
4.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 23
4.2. Approaches to Transport Header Protection . . . . . . . . 24
5. Addition of Transport Information to Network-Layer Headers . 26 5. Addition of Transport Information to Network-Layer Headers . 26
5.1. Use of OAM within a Maintenance Domain . . . . . . . . . 26 5.1. Use of OAM within a Maintenance Domain . . . . . . . . . 26
5.2. Use of OAM across Multiple Maintenance Domains . . . . . 26 5.2. Use of OAM across Multiple Maintenance Domains . . . . . 26
6. Implications of Protecting the Transport Headers . . . . . . 27 6. Implications of Protecting the Transport Headers . . . . . . 27
6.1. Independent Measurement . . . . . . . . . . . . . . . . . 27 6.1. Independent Measurement . . . . . . . . . . . . . . . . . 28
6.2. Characterising "Unknown" Network Traffic . . . . . . . . 29 6.2. Characterising "Unknown" Network Traffic . . . . . . . . 30
6.3. Accountability and Internet Transport Protocols . . . . . 30 6.3. Accountability and Internet Transport Protocols . . . . . 30
6.4. Impact on Operational Cost . . . . . . . . . . . . . . . 30 6.4. Impact on Operational Cost . . . . . . . . . . . . . . . 31
6.5. Impact on Research, Development and Deployment . . . . . 31 6.5. Impact on Research, Development and Deployment . . . . . 31
7. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 32 7. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 32
8. Security Considerations . . . . . . . . . . . . . . . . . . . 35 8. Security Considerations . . . . . . . . . . . . . . . . . . . 35
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 37 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 37
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 37 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 38
11. Informative References . . . . . . . . . . . . . . . . . . . 38 11. Informative References . . . . . . . . . . . . . . . . . . . 38
Appendix A. Revision information . . . . . . . . . . . . . . . . 45 Appendix A. Revision information . . . . . . . . . . . . . . . . 45
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 47 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 47
1. Introduction 1. Introduction
Transport protocols have supported end-to-end encryption of payload Transport protocols have supported end-to-end encryption of payload
data for many years. Examples include Transport Layer Security (TLS) data for many years. Examples include Transport Layer Security (TLS)
over TCP [RFC8446], Datagram TLS (DTLS) over UDP [RFC6347], and their over TCP [RFC8446], Datagram TLS (DTLS) over UDP [RFC6347], Secure
corresponding usage guidelines [RFC7525], Secure RTP [RFC3711], and RTP [RFC3711], and TCPcrypt [RFC8548] which permits opportunistic
TCPcrypt [RFC8548] which permits opportunistic encryption of the TCP encryption of the TCP transport payload. Some of these also provide
transport payload. Some of these also provide integrity protection integrity protection of all or part of the transport header.
of all or part of the transport header.
This end-to-end transport payload encryption brings many benefits in This end-to-end transport payload encryption brings many benefits in
terms of providing confidentiality and protecting user privacy. Such terms of providing confidentiality and protecting user privacy. The
benefits have been widely discussed [RFC7258] [RFC7624]. This benefits have been widely discussed, for example in [RFC7258] and
document strongly supports and encourages increased use of end-to-end [RFC7624]. This document strongly supports and encourages increased
payload encryption in transport protocols. The implications of use of end-to-end payload encryption in transport protocols. The
protecting the transport payload data are therefore not further implications of protecting the transport payload data are therefore
discussed in this document. not further discussed in this document.
A further level of protection can be achieved by encrypting the A further level of protection can be achieved by encrypting the
entire network layer payload, including both the transport layer entire network layer payload, including both the transport headers
headers and the payload. This method provides confidentiality for and the payload. This does not expose any transport information to
the entire transport packet. It therefore does not expose any devices in the network, and therefore also prevents modification
transport information to devices in the network, and prevents along a network path. An example of encryption at the network layer
modification along a network path. An example of encryption at the is the IPsec Encapsulating Security Payload (ESP) [RFC4303] in tunnel
network layer is the IPsec Encapsulating Security Payload (ESP) mode. Virtual Private Networks (VPNs) typically also operate in this
[RFC4303] in tunnel mode. Some Virtual Private Network (VPN) methods way. This form of encryption is not further discussed in this
also encrypt these headers. This form of encryption is not further document.
discussed in this document.
There is also a middle ground, comprising transport protocols that There is also a middle ground, comprising transport protocols that
encrypt some, or all, of their transport layer header information, in encrypt some, or all, of the transport layer header information, in
addition to the payload. An example of such a protocol, that is addition to encrypting the payload. An example of such a protocol,
seeing widespread interest and deployment, is the QUIC transport that is now seeing widespread interest and deployment, is the QUIC
protocol [I-D.ietf-quic-transport]. Encryption and authentication of transport protocol [I-D.ietf-quic-transport]. The encryption and
the transport header information can prevent unwanted modification of authentication of transport header information can prevent unwanted
transport headers by middleboxes. It also reduces the amount of modification of transport headers by middleboxes, reducing the risk
metadata about the progress of the transport connection that is of protocol ossification. It also reduces the amount of metadata
visible to the network. about the progress of the transport connection that is visible to the
network.
As discussed in [RFC7258], Pervasive Monitoring (PM) nis a technical As discussed in [RFC7258], Pervasive Monitoring (PM) is a technical
attack that needs to be mitigated in the design of IETF protocols. attack that needs to be mitigated in the design of IETF protocols.
This document supports that conclusion and the use of transport This document supports that conclusion and the use of transport
header encryption to protect against pervasive monitoring. RFC 7258 header encryption to protect against pervasive monitoring. RFC 7258
also notes, though, that "Making networks unmanageable to mitigate PM also notes, though, that "Making networks unmanageable to mitigate PM
is not an acceptable outcome, but ignoring PM would go against the is not an acceptable outcome, but ignoring PM would go against the
consensus documented here. An appropriate balance will emerge over consensus documented here. An appropriate balance will emerge over
time as real instances of this tension are considered". time as real instances of this tension are considered".
The following sections further considers some of the costs and The transport protocols developed for the Internet are used across a
changes to network management and research that are implied by wide range of paths across network segments with many different
widespread use of transport protocols that encrypt the transport regulatory, commercial, and engineering considerations. This
header information. It reviews the implications of developing document considers some of the costs and changes to network
transport protocols that use end-to-end encryption to provide management and research that are implied by widespread use of
confidentiality of their transport layer headers, and considers the transport protocols that encrypt their transport header information.
effect of such changes on transport protocol design and network It reviews the implications of developing transport protocols that
operations. It also considers some anticipated implications on use end-to-end encryption to provide confidentiality of their
transport and application evolution. That is, it considers the transport layer headers, and considers the effect of such changes on
issues in designing transport protocols that both protect their transport protocol design and network operations. It also considers
header information and respect user privacy. some anticipated implications on transport and application evolution.
This provides considerations relating to the design of transport
protocols that protect their header information and respect user
privacy.
2. Context and Rationale 2. Context and Rationale
The transport layer provides end-to-end interactions between The transport layer provides end-to-end interactions between
endpoints (processes) using an Internet path. Transport protocols endpoints (processes) using an Internet path. Transport protocols
layer directly over the network-layer service, and are sent in the layer over the network-layer service, and are usually sent in the
payload of network-layer packets. They support end-to-end payload of network-layer packets. They support end-to-end
communication between applications, using higher-layer protocols communication between applications, using higher-layer protocols
running on the end systems (transport endpoints). running on the end systems (transport endpoints).
This simple architectural view hides one of the core functions of the This simple architectural view does not present one of the core
transport: to discover and adapt to the Internet path that is functions of an Internet transport: to discover and adapt to the
currently being used. The design of Internet transport protocols is network path that is currently being used. The design of Internet
as much about trying to avoid the unwanted side effects of congestion transport protocols is as much about trying to avoid the unwanted
on a flow and other capacity-sharing flows, avoiding congestion side effects of congestion on a flow and other capacity-sharing
collapse, adapting to changes in the path characteristics, etc., as flows, avoiding congestion collapse, adapting to changes in the path
it is about end-to-end feature negotiation, flow control, and characteristics, etc., as it is about end-to-end feature negotiation,
optimising for performance of a specific application. flow control, and optimising for performance of a specific
application.
To achieve stable Internet operations, the IETF transport community Transport headers have end-to-end meaning, but have often been
has to date relied heavily on the results of measurements and the observed by equipment within the network. Transport protocol
insights of the network operations community to understand the trade- specifications have not tended to consider this, and have failed to
offs, and to inform selection of appropriate mechanisms to ensure a indicate what parts of the transport header are intended to be
safe, reliable, and robust Internet (e.g., [RFC1273]). In turn, the invariant across protocol versions and visible to the network; what
network operator and access provider communities have relied on being parts of the header can be modified by the network to signal to the
able to understand the pattern and requirements of traffic passing transport, and in what way; and what parts of the header are private
over the Internet, both in aggregate and at the flow level. The and/or expected to change in future, and need to be protected for
widespread use of transport header encryption could change this. privacy or to prevent protocol ossification.
Encryption is expected to form a core part of future transport Increasing concern about pervasive network monitoring
protocol designs. This can be in the form of encrypted transport [RFC7258][RFC7624], and growing awareness of the problem of protocol
protocols (i.e., transport protocols that use encryption to provide ossification caused by middlebox interference with Internet traffic,
confidentiality of some or all of the transport-layer header has motivated a shift in transport protocol design. Recent transport
information), and/or the encryption of transport payloads (i.e., protocols, such as QUIC [I-D.ietf-quic-transport], encrypt the
confidentiality of the payload data). There are many motivations for majority of their transport headers to prevent observation and
deploying such transports. Increasing public concerns about protect against modification by the network, and to make explicit
interference with Internet traffic [RFC7624] have led to a rapidly their invariants and what is intended to be visible to the network.
expanding deployment of encrypted transport protocols such as QUIC
[I-D.ietf-quic-transport].
Using encryption to provide confidentiality of the transport layer Transport header encryption is expected to form a core part of future
therefore brings some well-known privacy and security benefits. transport protocol designs. It can help to protect against pervasive
monitoring, improve privacy, and reduce protocol ossification.
Transport protocols that use header encryption with secure key
distribution can provide confidentiality and protection for some, or
all, of the transport header information, controlling what is visible
to, and can be modified by, the network.
The increased use of transport header encryption has benefits, but
also has implications for the broader ecosystem. The transport
community has, to date, relied heavily on measurements and insights
from the network operations community to understand protocol
behaviour, and to inform the selection of appropriate mechanisms to
ensure a safe, reliable, and robust Internet. In turn, network
operators and access providers have relied upon being able to observe
traffic patterns and requirements, both in aggregate and at the flow
level, to help understand and optimise the behaviour of their
networks. Widespread use of transport header encryption could limit
such observations in future. It is important to understand how
transport header information is used in the network, to allow future
protocol designs to make an informed choice on what, if any, headers
to expose to the network.
2.1. Use of Transport Header Information in the Network 2.1. Use of Transport Header Information in the Network
In-network measurement of transport flow characteristics can be used In-network measurement of transport flow characteristics can be used
to enhance performance, and control cost and service reliability. To to enhance performance, and control cost and service reliability. To
support network operations and enhance performance, some operators support network operations and enhance performance, some operators
have deployed functionality that utilises on-path observations of the have deployed functionality that utilises on-path observations of the
transport headers of packets passing through their network. These transport headers of packets passing through their network.
devices can rely on the presence and semantics of specific header
information, which leads to ossification where an endpoint has to When network devices rely on the presence of a header field or the
supply a specific header to receive the network service that it semantics of specific header information, this can lead to
desires. ossification where an endpoint has to supply a specific header to
receive the network service that it desires.
In some cases, network-layer use of transport header information can In some cases, network-layer use of transport header information can
be benign or advantageous to the protocol (e.g., recognising the be benign or advantageous to the protocol (e.g., recognising the
start of a TCP connection, providing header compression for a Secure start of a TCP connection, providing header compression for a Secure
RTP flow, or explicitly using exposed protocol information to provide RTP flow, or explicitly using exposed protocol information to provide
consistent decisions by on-path devices). However, in other cases, consistent decisions by on-path devices). However, in other cases,
ossification can frustrate the evolution of the transport protocol. this can have unwanted outcomes, e.g., privacy impacts and
A mechanism implemented in a network device, such as a firewall, that ossification.
Ossification can frustrate the evolution of a transport protocol. A
mechanism implemented in a network device, such as a firewall, that
requires a header field to have only a specific known set of values requires a header field to have only a specific known set of values
(i.e., that regards the field as invariant) can prevent the device can prevent the device from forwarding packets using a different
from forwarding packets using a different version of a protocol that version of the protocol that introduces a feature that changes to a
introduces a feature that changes the value of the observed field. new value for the observed field.
An example of such ossification was observed in the development of An example of ossification was observed in the development of
Transport Layer Security (TLS) 1.3 [RFC8446]. This necessitated a Transport Layer Security (TLS) 1.3 [RFC8446], where the design needed
design that recognised that deployed middleboxes relied on the to function in the presence of deployed middleboxes that relied on
presence of certain header fields exposed in TLS 1.2, and failed if the presence of certain header fields exposed in TLS 1.2.
those headers were changed.
The design of MPTCP also had to be revised to account for middleboxes The design of MPTCP also had to be revised to account for middleboxes
(known as "TCP Normalizers") that monitor the evolution of the window (known as "TCP Normalizers") that monitor the evolution of the window
advertised in the TCP header and reset connections when the window advertised in the TCP header and then reset connections when the
does not grow as expected. Similarly, Issues have been reported with window did not grow as expected. Similarly, issues have been
TCP Fast Open using middleboxes that modify the transport header of reported using TCP. For example, TCP Fast Open can experience
packets by removing unknown TCP options, that drop segments with middleboxes that modify the transport header of packets by removing
unknown TCP options, drop segments that contain data and have the SYN "unknown" TCP options, segments with unrecognised TCP options can be
bit set, drop packets with SYN/ACK that acknowledge data, or that dropped, segments that contain data and set the SYN bit can be
disrupt connections that send data before the three-way handshake dropped, or middleboxes that disrupt connections which send data
completes. Other examples of ossification have included middleboxes before completion of the three-way handshake. Other examples of
that rewrite TCP sequence and acknowledgement numbers, but are ossification have included middleboxes that rewrite TCP sequence and
unaware of the (newer) TCP selective acknowledgement (SACK) Option acknowledgement numbers, but are unaware of the (newer) TCP selective
and therefore fail to correctly rewrite the selective acknowledgement acknowledgement (SACK) Option and therefore fail to correctly rewrite
header information to match the changes that were made to the fixed the selective acknowledgement header information to match the changes
TCP header. that were made to the fixed TCP header, preventing SACK from
operating correctly.
In all these cases, the issue was caused by middleboxes that had a In all these cases, middleboxes with a hard-coded understanding of
hard-coded understanding of transport behaviour, and that interacted transport behaviour, interacted poorly with transport protocols after
poorly with transport protocols when the transport behaviour changed. the transport behaviour was changed.
Many protocol specifications had also failed to clearly indicate the
invariant parts of the transport header and were designed without
thought for how header information could be used within the network.
Transport header encryption can help reduce such ossification of the In contrast, transport header encryption prevents an on-path device
transport layer. A protocol design that uses header encryption with from observing the transport headers, and therefore stops mechanisms
secure key distribution can provide confidentiality for some, or all, being built that directly rely on or infer semantics of the transport
of the protocol header information. This prevents an on-path device header information. Encryption is normally combined with
from observing the transport headers, and stops mechanisms being authentication of the protected information. RFC 8546 summarises
built that directly rely on transport header information, or that this approach, stating that it is "The wire image, not the protocol's
seek to infer semantics of exposed header fields. This encryption is specification, determines how third parties on the network paths
normally combined with authentication of the protected information. among protocol participants will interact with that protocol"
RFC 8546 summarises this, stating that it is "The wire image, not the
protocol's specification, determines how third parties on the network
paths among protocol participants will interact with that protocol"
[RFC8546]. [RFC8546].
While encryption can hide transport header information and therefore While encryption can reduce ossification of the transport protocol,
help to reduce ossification of the transport protocol, it does not it does not itself prevent ossification of the network service.
prevent ossification of the network service. People seeking to People seeking to understand network traffic could still come to rely
understand network traffic could come to rely on pattern inferences on pattern inferences and other heuristics or machine learning to
and other heuristics as the basis for network decision and to derive derive measurement data and as the basis for network forwarding
measurement data. This can create new dependencies on the transport decisions. This can also create dependencies on the transport
protocol, or the patterns of traffic it can generate. This use of protocol, or the patterns of traffic it can generate.
machine-learning methods usually demands large data sets, presenting
it own requirements for collecting and distributing the data.
2.2. Authentication of Transport Header Information 2.2. Authentication of Transport Header Information
The design of a transport protocol needs to determine whether to The designers of a transport protocol decide whether to encrypt all,
encrypt all or a part of the transport information. It is possible or a part of, the transport header information. Section 4 of RFC8558
that on-path devices could develop mechanisms that rely on the states: "Anything exposed to the path should be done with the intent
presence of any non-encrypted field, or a known value in the field. that it be used by the network elements on the path" [RFC8558]. New
Section 4 of RFC8558 goes further, to state: "Anything exposed to the protocol designs can decide not to encrypt certain transport header
path should be done with the intent that it be used by the network fields, making those fields observable in the network. Where fields
elements on the path" [RFC8558]. In this context, specification of a are intended to immutable (i.e., observable but not modifiable by the
non-encrypted transport header field explicitly allows protocol network), the endpoints are encouraged to use authentication to
designers to make the certain header information observable by the provide a cryptographic integrity check that includes these immutable
network. This supports use of this information by on-path devices, fields to detect any manipulation by network devices.
but at the same time this can lead to ossification of the exposed
part of a transport header. That is, network forwarding could evolve
to depend on the presence and/or value of these fields (even if the
header is not modified by the in-network device).
New protocol designs will make use of authentication to provide a
cryptographic integrity check for the transport header fields.
Transport header information that is authenticated, but not
encrypted, permits inspection of the non-encrypted header fields by
devices on the path, but does prevent undetected manipulation by
network devices.
Sometimes a protocol design employs a header field that is not Making part of a transport header observable can lead to ossification
encrypted, but it is desired to avoid unwanted inspection restricting of that part of a header, as middleboxes come to rely on observations
the choice of usable values in the field (and the resulting potential of the exposed fields. A protocol design that provides an observable
for undesirable ossification). In this case, the protocol designers field might want to avoid inspection restricting the choice of usable
can choose to intentionally vary the format and/or value of exposed values in the field by intentionally varying the format and/or value
header fields to reduce the chance of ossification (see Section 4 and of the field to reduce the chance of ossification (see Section 4).
[I-D.ietf-tls-grease]).
2.3. Observable Transport Header Fields 2.3. Observable Transport Header Fields
Transport headers have end-to-end meaning, but are often observed by Transport headers fields have been observed within the network for a
equipment within the network. The decision about which transport variety of purposes. Some of these are related to network management
headers fields are made observable offers trade-offs around header and operations. The lists below, and in the following section, seek
confidentiality versus header observability (including non-encrypted to identify some of these uses and the implications of the increased
but authenticated header fields) for network operations and use of transport header encryption. This analysis does not judge
management, and the implications for ossification and user privacy. whether specific practises are necessary, or endorse the use of any
The impact differs depending on the activity, as discussed below and specific approach.
developed in the remainder of this document:
Network Operations: Observable transport headers enable explicit Network Operations: Observable transport headers enable explicit
measurement and analysis of protocol performance, measurement and analysis of protocol performance,
network anomalies, and failure pathologies at any network anomalies, and failure pathologies at any
point along the Internet path. In many cases, it point along the Internet path. In many cases, it
is important to relate observations to specific is important to relate observations to specific
equipment/configurations or a specific network equipment/configurations, to a specific network
segment. segment, or sometimes to a specific protocol or
application.
Concealing transport header information makes When transport header information is not
performance/behaviour unavailable to passive observable, it cannot be used by network
observers along the path. Operators will then be operators. Operators might work without that
unable to use this information directly and could information, or they might turn to more ambitious
turn to more ambitious ways to collect, estimate, ways to collect, estimate, or infer this data.
or infer that data. (Operational practices aimed (Operational practises aimed at guessing
at guessing transport parameters are out of scope transport parameters are out of scope for this
for this document, and are only mentioned here to document, and are only mentioned here to
recognize that encryption does not stop operators recognize that encryption does not stop operators
from attempting to apply practices that have been from attempting to apply practises that have been
used with unencrypted transport headers.) used with unencrypted transport headers.)
See also Sections 3, 5, and 6.4. See also Sections 3, 5, and 6.4.
Traffic Analysis: Observable transport headers can be used to Traffic Analysis: Observable transport headers have been used to
determine which transport protocols and features determine which transport protocols and features
are being used across a network segment, and to are being used across a network segment, and to
measure trends in the pattern of usage. For some measure trends in the pattern of usage. For some
use cases, end-to-end measurements/traces are use cases, end-to-end measurements/traces are
sufficient and can assist in developing and sufficient and can assist in developing and
debugging new transports and analysing their debugging new transports and analysing their
deployment. In other uses, it is important to deployment. In other uses, it is important to
relate observations to specific equipment/ relate observations to specific equipment/
configurations or particular network segments. configurations or particular network segments.
Concealing transport header information can make This information can help anticipate the demand
analysis harder or impossible. This could impact for network upgrades and roll-out, or affect on-
the ability to anticipate the need for network going traffic engineering activities performed by
upgrades and roll-out, or affect on-going traffic operators such as determining which parts of the
engineering activities performed by operators path contribute delay, jitter, or loss.
such as determining which parts of the path
contribute delay, jitter, or loss. While this Tools that rely upon observing headers, could
impact could, in many cases, be small, there are fail to produce useful data when those headers
scenarios where operators will actively monitor are encrypted. While this impact could, in many
and support particular services, e.g., to explore cases, be small, there are scenarios where
issues relating to Quality of Service (QoS), to operators have actively monitored and supported
perform fast re-routing of critical traffic, to particular services, e.g., to explore issues
mitigate the characteristics of specific radio relating to Quality of Service (QoS), to perform
links, and so on. fast re-routing of critical traffic, to mitigate
the characteristics of specific radio links, and
so on.
See also Sections 3.1-3.2, and 5. See also Sections 3.1-3.2, and 5.
Troubleshooting: Observable transport headers can be utilised by Troubleshooting: Observable transport headers have been utilised
operators for network troubleshooting and by operators as a part of network troubleshooting
diagnostics. Effective troubleshooting often and diagnostics. Metrics can help localise the
requires visibility into the transport layer network segment introducing the loss or latency.
behaviour. Flows experiencing packet loss or Effective troubleshooting often requires
jitter are hard to distinguish from unaffected understanding of transport behaviour. Flows
flows when only observing network layer headers. experiencing packet loss or jitter are hard to
distinguish from unaffected flows when only
observing network layer headers.
Concealing transport header information reduces Observable transport feedback information (e.g.,
the incentive for operators to troubleshoot, RTP Control Protocol (RTCP) reception reports
since they cannot interpret the data. This can [RFC3550]) can explicitly make loss metrics
limit understanding of transport dynamics, such visible to operators. Loss metrics can also be
as the impact of packet loss or latency on the deduced with more complexity from other header
flows, or make it harder to localise the network information (e.g., by observing TCP SACK blocks).
segment introducing the packet loss or latency. When the transport header information is
Additional mechanisms will be needed to help encrypted, explicit observable fields could also
reconstruct or replace transport-level metrics be made available at the network or transport
for troubleshooting and diagnostics. These can layers to provide these functions.
add complexity and operational costs (e.g., in
deploying additional functions in equipment or
adding traffic overhead).
See also Section 3.3 and 5. See also Section 3.3 and 5.
Network Protection: Observable transport headers currently provide Network Protection: Observable transport headers currently provide
useful input to classify and detect anomalous useful input to classify and detect anomalous
events, such as changes in application behaviour events, such as changes in application behaviour
or distributed denial of service attacks. An or distributed denial of service attacks.
operator needs to uniquely disambiguate unwanted Operators often seek to uniquely disambiguate
traffic. unwanted traffic.
Concealing transport header information would Where flows cannot be disambiguated based on
prevent disambiguation based on transport transport information, this could result in less-
information. This could result in less-efficient efficient identification of unwanted traffic, the
identification of unwanted traffic, the use of
heuristics to identify anomalous flows, or the
introduction of rate limits for uncharacterised introduction of rate limits for uncharacterised
traffic. traffic, or the use of heuristics to identify
anomalous flows.
See also Sections 6.2 and 6.3. See also Sections 6.2 and 6.3.
Verifiable Data: Observable transport headers can provide open and
verifiable measurements to support operations,
research, and protocol development. The ability
of multiple stake holders to review transport
header traces helps develop insight into
performance and traffic contribution of specific
variants of a protocol. Independently observed
data is important to help ensure the health of
the research and development communities.
When transport header information can not be
observed, this can reduce the range of actors
that can observe data. This limits the
information sources available to the Internet
community to understand the operation of new
transport protocols, reducing information to
inform design decisions and standardisation of
the new protocols and related operational
practises
See also Section 6.
SLA Compliance: Observable transport headers coupled with SLA Compliance: Observable transport headers coupled with
published transport specifications allow published transport specifications allow
operators and regulators to explore teh operators and regulators to explore the
compliance with Service Level Agreements (SLAs). compliance with Service Level Agreements (SLAs).
Independently verifiable performance metrics can
also be utilised to demonstrate regulatory
compliance in some jurisdictions, and as a basis
for informing design decisions. This can bring
assurance to those operating networks, often
avoiding the need to deploy complex techniques
that routinely monitor and manage Internet
traffic flows (e.g., avoiding the capital and
operational costs of deploying flow rate-limiting
and network circuit-breaker methods [RFC8084]).
When transport header information is concealed, When transport header information can not be
it is not possible to observe transport header observed, other methods have to be found to
information. Methods are still needed to confirm confirm that the traffic produced conforms to the
that the traffic produced conforms to the
expectations of the operator or developer. expectations of the operator or developer.
See also Sections 5 and 6.1-6.3. Independently verifiable performance metrics can
be utilised to demonstrate regulatory compliance
Verifiable Data: Observable transport headers can provide open and in some jurisdictions, and as a basis for
verifiable measurements to support operations, informing design decisions. This can bring
research, and protocol development. The ability assurance to those operating networks, often
of other stake holders to review transport header avoiding deployment of complex techniques that
traces helps develop insight into performance and routinely monitor and manage Internet traffic
traffic contribution of specific variants of a flows (e.g., avoiding the capital and operational
protocol. Independently observed data is costs of deploying flow rate-limiting and network
important to help ensure the health of the circuit-breaker methods [RFC8084]).
research and development communities.
Concealing transport header information can
reduce the range of actors that can observe
useful data. This limits the information sources
available to the Internet community to understand
the operation of new transport protocols,
reducing information to inform design decisions
and standardisation of the new protocols and
related operational practices
See also Section 6. See also Sections 5 and 6.1-6.3.
There are architectural challenges and considerations in the way Note, again, that this lists uses that have been made of transport
transport protocols are designed, and the ability to characterise and header information, and does not necessarily endorse any particular
compare different transport solutions [Measure]. Different parties approach.
will view the relative importance of these differently. For some,
the benefits of encrypting the transport headers could outweigh the
impact of doing so; others might make a different trade-off.
3. Current uses of Transport Headers within the Network 3. Current uses of Transport Headers within the Network
In response to pervasive monitoring [RFC7624] revelations and the In response to pervasive monitoring [RFC7624] revelations and the
IETF consensus that "Pervasive Monitoring is an Attack" [RFC7258], IETF consensus that "Pervasive Monitoring is an Attack" [RFC7258],
efforts are underway to increase encryption of Internet traffic. efforts are underway to increase encryption of Internet traffic.
Applying confidentiality to transport header fields affects how Applying confidentiality to transport header fields affects how
protocol information is used [RFC8404], requiring consideration of protocol information is used [RFC8404], requiring consideration of
the trade-offs discussed in Section 2.3. To understand the the trade-offs discussed in Section 2.3.
implications, it is necessary to understand how transport layer
headers are currently observed and/or modified by middleboxes within
the network.
This section reviews some current usage. This review does not There are architectural challenges and considerations in the way
consider the intentional modification of transport headers by transport protocols are designed, and the ability to characterise and
middleboxes (such as in Network Address Translation, NAT, or compare different transport solutions [Measure]. The decision about
Firewalls). Common issues concerning IP address sharing are which transport headers fields are made observable offers trade-offs
described in [RFC6269]. around header confidentiality versus header observability (including
non-encrypted but authenticated header fields) for network operations
and management, and the implications for ossification and user
privacy. Different parties will view the relative importance of
these differently. For some, the benefits of encrypting all
transport headers outweigh the impact of doing so; others might
analyse the security, privacy and ossification impacts and arrive at
a different trade-off.
3.1. Observing Transport Information in the Network To understand the implications, it is necessary to understand how
transport layer headers are currently observed and/or modified by
middleboxes within the network. This section therefore reviews
examples of current usage. It does not consider the intentional
modification of transport headers by middleboxes (such as in Network
Address Translation, NAT, or Firewalls). Common issues concerning IP
address sharing are described in [RFC6269].
If in-network observation of transport protocol headers is needed, 3.1. Observing Transport Information in the Network
this requires knowledge of the format of the transport header:
o Flows need to be identified at the level needed to perform the In-network observation of transport protocol headers requires
observation; knowledge of the format of the transport header:
o The protocol and version of the header need to be visible, e.g., o Flows have to be identified at the level where observation is
by defining the wire image [RFC8546]. As protocols evolve over performed. This implies visibility of the protocol and version of
time and there could be a need to introduce new transport headers. the header, e.g., by defining the wire image [RFC8546]. As
This could require interpretation of protocol version information protocols evolve over time, new transport headers could be
or connection setup information; introduced. Detecting this could require interpretation of
protocol version information or connection setup information;
o The location and syntax of any observed transport headers need to o Observing transport information depends on knowing the location
be known. IETF transport protocols can specify this information. and syntax of the observed transport headers. IETF transport
protocols can specify this information.
The following subsections describe various ways that observable The following subsections describe various ways that observable
transport information has been utilised. transport information has been utilised.
3.1.1. Flow Identification Using Transport Layer Headers 3.1.1. Flow Identification Using Transport Layer Headers
Flow/Session identification [RFC8558] is a common function. For Flow/Session identification [RFC8558] is a common function. For
example, performed by measurement activities, QoS classification, example, performed by measurement activities, QoS classification,
firewalls, Denial of Service, DOS, prevention. firewalls, Denial of Service, DOS, prevention.
Observable transport header information, together with information in Observable transport header information, together with information in
the network header, has been used to identify flows and their the network header, has been used to identify flows and their
connection state, together with the protocol options being used. connection state, together with the set of protocol options being
Transport protocols, such as TCP and the Stream Control Transport used. Transport protocols, such as TCP and the Stream Control
Protocol (SCTP), specify a standard base header that includes Transport Protocol (SCTP), specify a standard base header that
sequence number information and other data. They also have the includes sequence number information and other data. They also have
possibility to negotiate additional headers at connection setup, the possibility to negotiate additional headers at connection setup,
identified by an option number in the transport header. identified by an option number in the transport header.
In some uses, a low-numbered (well-known) transport port number can In some uses, a low-numbered (well-known) transport port number can
identify the protocol. However, port information alone is not identify the protocol. However, port information alone is not
sufficient to guarantee identification when applications can use sufficient to guarantee identification. Applications can use
arbitrary ports, multiple sessions can be multiplexed on a single arbitrary ports, multiple sessions can be multiplexed on a single
port, and ports can be re-used by subsequent sessions. UDP-based port, and ports can be re-used by subsequent sessions. UDP-based
protocols often do not use well-known port numbers. Some flows can protocols often do not use well-known port numbers. Some flows can
instead be identified by observing signalling protocol data (e.g., be identified by observing signalling protocol data (e.g., [RFC3261],
[RFC3261], [I-D.ietf-rtcweb-overview]) or through the use of magic [I-D.ietf-rtcweb-overview]) or through the use of magic numbers
numbers placed in the first byte(s) of the datagram payload placed in the first byte(s) of the datagram payload [RFC7983].
[RFC7983].
Concealing transport header information can remove information used When transport header information can not be observed, this removes
to classify flows by passive observers along the path, so operators information that could be used to classify flows by passive observers
will be unable to use this information directly. Operators could along the path. More ambitious ways could be used to collect,
turn to more ambitious ways to collect, estimate, or infer that data, estimate, or infer flow information, including heuristics based on
including heuristics based on the analysis of traffic patterns. For the analysis of traffic patterns. For example, an operator that
example, an operator that cannot access the Session Description cannot access the Session Description Protocol (SDP) session
Protocol (SDP) session descriptions to classify a flow as audio descriptions to classify a flow as audio traffic, might instead use
traffic, might instead use (possibly less-reliable) heuristics to (possibly less-reliable) heuristics to infer that short UDP packets
infer that short UDP packets with regular spacing carry audio with regular spacing carry audio traffic. Operational practises
traffic. Operational practices aimed at inferring transport aimed at inferring transport parameters are out of scope for this
parameters are out of scope for this document, and are only mentioned document, and are only mentioned here to recognize that encryption
here to recognize that encryption does not prevent operators from does not prevent operators from attempting to apply practises that
attempting to apply practices that were used with unencrypted were used with unencrypted transport headers.
transport headers.
3.1.2. Metrics derived from Transport Layer Headers 3.1.2. Metrics derived from Transport Layer Headers
Observable transport headers enable explicit measurement and analysis Observable transport headers enable explicit measurement and analysis
of protocol performance, network anomalies, and failure pathologies of protocol performance, network anomalies, and failure pathologies
at any point along the Internet path. Some operators use passive at any point along the Internet path. Some operators use passive
monitoring to manage their portion of the Internet by characterizing monitoring to manage their portion of the Internet by characterizing
the performance of link/network segments. Inferences from transport the performance of link/network segments. Inferences from transport
headers are used to derive performance metrics. A variety of open headers are used to derive performance metrics. A variety of open
source and commercial tools have been deployed that utilise transport source and commercial tools have been deployed that utilise transport
header information in this way to derive the following metrics: header information in this way to derive the following metrics:
Traffic Rate and Volume: Protocol sequence number and packet size Traffic Rate and Volume: Protocol sequence number and packet size
can be used to derive volume measures per-application, to could be used to derive volume measures per-application, to
characterise the traffic that uses a network segment or the characterise the traffic that uses a network segment or the
pattern of network usage. Measurements can be per endpoint or for pattern of network usage. Measurements can be per endpoint or for
an endpoint aggregate (e.g., to assess subscriber usage). an endpoint aggregate (e.g., to assess subscriber usage).
Measurments can also be used to trigger traffic shaping, and to Measurements can also be used to trigger traffic shaping, and to
associate QoS support within the network and lower layers. Volume associate QoS support within the network and lower layers. Volume
measures can also be valuable for capacity planning and providing measures can also be valuable for capacity planning and providing
detail of trends in usage. detail of trends in usage. The traffic rate and volume can be
determined providing that the packets belonging to individual
flows can be identified, but there might be no additional
information about a flow when the transport headers cannot be
observed.
Loss Rate and Loss Pattern: Flow loss rate can be derived (e.g., Loss Rate and Loss Pattern: Flow loss rate can be derived (e.g.,
from transport sequence numbers) and has been used as a metric for from transport sequence numbers or inferred from observing
transport protocol interactions) and has been used as a metric for
performance assessment and to characterise transport behaviour. performance assessment and to characterise transport behaviour.
Understanding the location and root cause of loss can help an Understanding the location and root cause of loss can help an
operator determine whether this requires corrective action. operator determine whether this requires corrective action.
Network operators have used the variation in patterns of loss as a Network operators have used the variation in patterns of loss as a
key performance metric, utilising this to detect changes in the key performance metric, utilising this to detect changes in the
offered service. offered service.
There are various causes of loss, including: corruption of link There are various causes of loss, including: corruption of link
frames (e.g., due to interference on a radio link), buffering loss frames (e.g., due to interference on a radio link), buffering loss
(e.g., overflow due to congestion, Active Queue Management, AQM (e.g., overflow due to congestion, Active Queue Management, AQM
[RFC7567], or inadequate provision following traffic pre-emption), [RFC7567], or inadequate provision following traffic pre-emption),
and policing (traffic management). Understanding flow loss rates and policing (traffic management). Understanding flow loss rates
requires either observing sequence numbers in transport headers, requires either observing sequence numbers in network or transport
or maintaining per-flow packet counters (flow identification often headers, or maintaining per-flow packet counters (flow
requires transport header information). Per-hop loss can also identification often requires transport header information). Per-
sometimes be monitored at the interface level by devices in the hop loss can also sometimes be monitored at the interface level by
network. It is often valuable to understand the conditions under devices in the network.
which packet loss occurs, which usually requires relating loss to
the traffic flowing on the network node/segment at the time of
loss.
Observation of transport feedback information (e.g., RTP Control Losses can often occur as bursts, randomly-timed events, etc. The
Protocol (RTCP) reception reports [RFC3550], TCP SACK blocks) can pattern of loss can provide insight into the cause of loss. It
increase understanding of the impact of loss and help identify can also be valuable to understand the conditions under which loss
cases where loss could have been wrongly identified, or where the occurs, which usually requires relating loss to the traffic
transport did not require transmission of the lost packet. It is flowing on the network node/segment at the time of loss. This can
sometimes more helpful to understand the pattern of loss, than the also help identify cases where loss could have been wrongly
loss rate, because losses can often occur as bursts, rather than identified, or where the transport did not require transmission of
randomly-timed events. a lost packet.
Throughput and Goodput: Throughput is the amount of data sent by a Throughput and Goodput: Throughput is the amount of payload data
flow per time interval. Goodput [RFC7928] is a measure of useful sent by a flow per time interval. Goodput [RFC7928] is a measure
data exchanged (the ratio of useful data to total volume of of useful data exchanged (the ratio of useful data to total volume
traffic sent by a flow). The throughput of a flow can be of traffic sent by a flow). The throughput of a flow can be
determined even when transport header information is concealed, determined in the absence of transport header information,
providing the individual flow can be identified. Goodput requires providing that the individual flow can be identified, and the
ability to differentiate loss and retransmission of packets, for overhead known. Goodput requires ability to differentiate loss
example by observing packet sequence numbers in the TCP or the and retransmission of packets, for example by observing packet
Real-time Transport Protocol (RTP) headers [RFC3550]. sequence numbers in the TCP or the Real-time Transport Protocol
(RTP) headers [RFC3550].
Latency: Latency is a key performance metric that impacts Latency: Latency is a key performance metric that impacts
application and user-perceived response times. It often application and user-perceived response times. It often
indirectly impacts throughput and flow completion time. This indirectly impacts throughput and flow completion time. This
determines the reaction time of the transport protocol itself, determines the reaction time of the transport protocol itself,
impacting flow setup, congestion control, loss recovery, and other impacting flow setup, congestion control, loss recovery, and other
transport mechanisms. The observed latency can have many transport mechanisms. The observed latency can have many
components [Latency]. Of these, unnecessary/unwanted queuing in components [Latency]. Of these, unnecessary/unwanted queuing in
network buffers has often been observed as a significant factor network buffers has often been observed as a significant factor
[bufferbloat]. Once the cause of unwanted latency has been [bufferbloat]. Once the cause of unwanted latency has been
identified, this can often be eliminated. identified, this can often be eliminated.
To measure latency across a part of a path, an observation point To measure latency across a part of a path, an observation point
[RFC7799] can measure the experienced round trip time (RTT) using [RFC7799] can measure the experienced round trip time (RTT) using
packet sequence numbers, and acknowledgements, or by observing packet sequence numbers and acknowledgements, or by observing
header timestamp information. Such information allows an header timestamp information. Such information allows an
observation point in the network to determine not only the path observation point in the network to determine not only the path
RTT, but also allows measurement of the upstream and downstream RTT, but also allows measurement of the upstream and downstream
contribution to the RTT. This could be used to locate a source of contribution to the RTT. This could be used to locate a source of
latency, e.g., by observing cases where the median RTT is much latency, e.g., by observing cases where the median RTT is much
greater than the minimum RTT for a part of a path. greater than the minimum RTT for a part of a path.
The service offered by network operators can benefit from latency The service offered by network operators can benefit from latency
information to understand the impact of configuration changes and information to understand the impact of configuration changes and
to tune deployed services. Latency metrics are key to evaluating to tune deployed services. Latency metrics are key to evaluating
skipping to change at page 14, line 23 skipping to change at page 14, line 36
[RFC8290] and although parameter-less methods are desired [RFC8290] and although parameter-less methods are desired
[RFC7567], current methods often require tuning [RFC8290] [RFC7567], current methods often require tuning [RFC8290]
[RFC8289] [RFC8033] because they cannot scale across all possible [RFC8289] [RFC8033] because they cannot scale across all possible
deployment scenarios. deployment scenarios.
Variation in delay: Some network applications are sensitive to Variation in delay: Some network applications are sensitive to
(small) changes in packet timing (jitter). Short and long-term (small) changes in packet timing (jitter). Short and long-term
delay variation can impact on the latency of a flow and hence the delay variation can impact on the latency of a flow and hence the
perceived quality of applications using the network. For example, perceived quality of applications using the network. For example,
jitter metrics are often cited when characterising paths jitter metrics are often cited when characterising paths
supporting real-time traffic. To assess the performance of such supporting real-time traffic. The expected performance of such
applications, it can be necessary to measure the variation in applications, can be inferred from a measure the variation in
delay observed along a portion of the path [RFC3393] [RFC5481]. delay observed along a portion of the path [RFC3393] [RFC5481].
The requirements for observable transport headers resemble those The requirements resemble those for the measurement of latency.
for the measurement of latency.
Flow Reordering: Significant packet reordering within a flow can Flow Reordering: Significant packet reordering within a flow can
impact time-critical applications and can be interpreted as loss impact time-critical applications and can be interpreted as loss
by reliable transports. Many transport protocol techniques are by reliable transports. Many transport protocol techniques are
impacted by reordering (e.g., triggering TCP retransmission or re- impacted by reordering (e.g., triggering TCP retransmission or re-
buffering of real-time applications). Packet reordering can occur buffering of real-time applications). Packet reordering can occur
for many reasons, from equipment design to misconfiguration of for many reasons, from equipment design to misconfiguration of
forwarding rules. Since this impacts transport performance, forwarding rules. Network tools can detect and measure unwanted/
network tools are needed to detect and measure unwanted/excessive excessive reordering, and the impact on transport performance.
reordering.
There have been initiatives in the IETF transport area to reduce There have been initiatives in the IETF transport area to reduce
the impact of reordering within a transport flow, possibly leading the impact of reordering within a transport flow, possibly leading
to a reduction in the requirements for preserving ordering. These to a reduction in the requirements for preserving ordering. These
have potential to simplify network equipment design as well as the have potential to simplify network equipment design as well as the
potential to improve robustness of the transport service. potential to improve robustness of the transport service.
Measurements of reordering can help understand the present level Measurements of reordering can help understand the present level
of reordering within deployed infrastructure, and inform decisions of reordering within deployed infrastructure, and inform decisions
about how to progress such mechanisms. Key performance indicators about how to progress such mechanisms. Key performance indicators
are retransmission rate, packet drop rate, sector utilisation are retransmission rate, packet drop rate, sector utilisation
skipping to change at page 15, line 14 skipping to change at page 15, line 22
Metrics have been defined that evaluate whether a network has Metrics have been defined that evaluate whether a network has
maintained packet order on a packet-by-packet basis [RFC4737] maintained packet order on a packet-by-packet basis [RFC4737]
[RFC5236]. [RFC5236].
Techniques for measuring reordering typically observe packet Techniques for measuring reordering typically observe packet
sequence numbers. Some protocols provide in-built monitoring and sequence numbers. Some protocols provide in-built monitoring and
reporting functions. Transport fields in the RTP header [RFC3550] reporting functions. Transport fields in the RTP header [RFC3550]
[RFC4585] can be observed to derive traffic volume measurements [RFC4585] can be observed to derive traffic volume measurements
and provide information on the progress and quality of a session and provide information on the progress and quality of a session
using RTP. As with other measurement, metadata is often needed to using RTP. As with other measurement, metadata assist in
understand the context under which the data was collected, understanding the context under which the data was collected,
including the time, observation point [RFC7799], and way in which including the time, observation point [RFC7799], and way in which
metrics were accumulated. The RTCP protocol directly reports some metrics were accumulated. The RTCP protocol directly reports some
of this information in a form that can be directly visible in the of this information in a form that can be directly visible in the
network. A user of summary measurement data needs to trust the network. A user of summary measurement data has to trust the
source of this data and the method used to generate the summary source of this data and the method used to generate the summary
information. information.
This information can support network operations, inform capacity These metrics can support network operations, inform capacity
planning, and assist in determining the need for equipment and/or planning, and assist in determining the demand for equipment and/or
configuration changes by network operators. It can also inform configuration changes by network operators. They can also inform
Internet engineering activities by informing the development of new Internet engineering activities by informing the development of new
protocols, methodologies, and procedures. protocols, methodologies, and procedures.
In some cases, measurements could involve active injection of test
traffic to perform a measurement (see section 3.4 of [RFC7799]).
However, most operators do not have access to user equipment,
therefore the point of test is normally different from the transport
endpoint. Injection of test traffic can incur an additional cost in
running such tests (e.g., the implications of capacity tests in a
mobile network are obvious). Some active measurements [RFC7799]
(e.g., response under load or particular workloads) perturb other
traffic, and could require dedicated access to the network segment.
Passive measurements (see section 3.6 of [RFC7799]) can have
advantages in terms of eliminating unproductive test traffic,
reducing the influence of test traffic on the overall traffic mix,
and the ability to choose the point of observation (see
Section 3.2.1). Measurements can rely on observing packet headers,
which is not possible if those headers are encrypted, but could
utilise information about traffic volumes or patterns of interaction
to deduce metrics.
An alternative approach is to use in-network techniques add and
observe packet headers to facilitate measurements while traffic
traverses an operational network. This approach does not require the
cooperation of an endpoint.
3.1.3. Transport use of Network Layer Header Fields 3.1.3. Transport use of Network Layer Header Fields
Information from the transport protocol can be used by a multi-field Information from the transport protocol is used by a multi-field
classifier as a part of policy framework. Policies are commonly used classifier as a part of policy framework. Policies are commonly used
for management of the QoS or Quality of Experience (QoE) in resource- for management of the QoS or Quality of Experience (QoE) in resource-
constrained networks, and by firewalls to implement access rules (see constrained networks, and by firewalls to implement access rules (see
also section 2.2.2 of [RFC8404]). Network-layer classification also section 2.2.2 of [RFC8404]). Network-layer classification
methods that rely on a multi-field classifier (e.g., inferring QoS methods that rely on a multi-field classifier (e.g., inferring QoS
from the 5-tuple or choice of application protocol) are incompatible from the 5-tuple or choice of application protocol) are incompatible
with transport protocols that encrypt the transport information. with transport protocols that encrypt the transport information.
Traffic that cannot be classified will typically receive a default Traffic that cannot be classified typically receives a default
treatment. treatment.
Transport information can also be explicitly set in network-layer Transport information can also be explicitly set in network-layer
header fields that are not encrypted, serving as a replacement/ header fields that are not encrypted, serving as a replacement/
addition to the exposed transport information [RFC8558]. This can addition to the exposed transport information [RFC8558]. This
provide information to enable a different forwarding treatment by the information can enable a different forwarding treatment by the
network, even when a transport employs encryption to protect other network, even when a transport employs encryption to protect other
header information. header information.
The user of a transport that multiplexes multiple sub-flows might The user of a transport that multiplexes multiple sub-flows might
want to hide the presence and characteristics of these sub-flows. On want to obscure the presence and characteristics of these sub-flows.
the other hand, an encrypted transport could set the network-layer On the other hand, an encrypted transport could set the network-layer
information to indicate the presence of sub-flows, and to reflect the information to indicate the presence of sub-flows, and to reflect the
network needs of individual sub-flows. There are several ways this service requirements of individual sub-flows. There are several ways
could be done: this could be done:
IP Address: Applications normally expose the addresses used by IP Address: Applications normally expose the addresses used by
endpoints, and this is used in the forwarding decisions in network endpoints, and this is used in the forwarding decisions in network
devices. Address and other protocol information can be used by a devices. Address and other protocol information can be used by a
Multi-Field (MF) classifier to determine how traffic is treated Multi-Field (MF) classifier to determine how traffic is treated
[RFC2475], and hence the quality of experience for a flow. [RFC2475], and hence the quality of experience for a flow.
Using the IPv6 Network-Layer Flow Label: A number of Standards Track Using the IPv6 Network-Layer Flow Label: A number of Standards Track
and Best Current Practice RFCs (e.g., [RFC8085], [RFC6437], and Best Current Practice RFCs (e.g., [RFC8085], [RFC6437],
[RFC6438]) encourage endpoints to set the IPv6 Flow label field of [RFC6438]) encourage endpoints to set the IPv6 Flow label field of
the network-layer header. IPv6 "source nodes SHOULD assign each the network-layer header. IPv6 "source nodes SHOULD assign each
unrelated transport connection and application data stream to a unrelated transport connection and application data stream to a
new flow" [RFC6437]. A multiplexing transport could choose to use new flow" [RFC6437]. A multiplexing transport could choose to use
multiple Flow labels to allow the network to independently forward multiple Flow labels to allow the network to independently forward
subflows. RFC6437 provides further guidance on choosing a flow sub-flows. RFC6437 provides further guidance on choosing a flow
label value, stating these "should be chosen such that their bits label value, stating these "should be chosen such that their bits
exhibit a high degree of variability", and chosen so that "third exhibit a high degree of variability", and chosen so that "third
parties should be unlikely to be able to guess the next value that parties should be unlikely to be able to guess the next value that
a source of flow labels will choose". a source of flow labels will choose".
Once set, a flow label can provide information that can help Once set, a flow label can provide information that can help
inform network-layer queuing and forwarding [RFC6438], for example inform network-layer queuing and forwarding [RFC6438], for example
with Equal Cost Multi-Path routing and Link Aggregation [RFC6294]. with Equal Cost Multi-Path routing and Link Aggregation [RFC6294].
Considerations when using IPsec are further described in Considerations when using IPsec are further described in
[RFC6438]. [RFC6438].
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Using the Network-Layer Differentiated Services Code Point: Using the Network-Layer Differentiated Services Code Point:
Applications can expose their delivery expectations to the network Applications can expose their delivery expectations to the network
by setting the Differentiated Services Code Point (DSCP) field of by setting the Differentiated Services Code Point (DSCP) field of
IPv4 and IPv6 packets [RFC2474]. For example, WebRTC applications IPv4 and IPv6 packets [RFC2474]. For example, WebRTC applications
identify different forwarding treatments for individual sub-flows identify different forwarding treatments for individual sub-flows
(audio vs. video) based on the value of the DSCP field (audio vs. video) based on the value of the DSCP field
[I-D.ietf-tsvwg-rtcweb-qos]). This provides explicit information [I-D.ietf-tsvwg-rtcweb-qos]). This provides explicit information
to inform network-layer queuing and forwarding, rather than an to inform network-layer queuing and forwarding, rather than an
operator inferring traffic requirements from transport and operator inferring traffic requirements from transport and
application headers via a multi-field classifier. Inappropriate application headers via a multi-field classifier. Inappropriate
use can have privacy implications (e.g., assigning the same label use by the transport can have privacy implications (e.g.,
to two independent flows that ought not to be classified the assigning a different DSCP to a subflow could assist in a network
same). Inappropriate use by the transport can have privacy device discovering the traffic pattern used by an application,
implications (e.g., assigning a different DSCP to a subflow could assigning the same label to two independent flows that ought not
assist in a network device discovering the traffic pattern used by to be classified the same). The field is mutable, i.e., some
an application). The field is mutable, i.e., some network devices network devices can be expected to change this field (use of each
can be expected to change this field (use of each DSCP value is DSCP value is defined by an RFC).
defined by an RFC).
Since the DSCP value can impact the quality of experience for a Since the DSCP value can impact the quality of experience for a
flow, observations of service performance need to consider this flow, observations of service performance has to consider this
field when a network path has support for differentiated service field when a network path supports differentiated service
treatment. treatment.
Using Explicit Congestion Marking: ECN [RFC3168] is a transport Using Explicit Congestion Marking: ECN [RFC3168] is a transport
mechanism that utilises the ECN field in the network-layer header. mechanism that utilises the ECN field in the network-layer header.
Use of ECN explicitly informs the network-layer that a transport Use of ECN explicitly informs the network-layer that a transport
is ECN-capable, and requests ECN treatment of the flow. An ECN- is ECN-capable, and requests ECN treatment of the flow. An ECN-
capable transport can offer benefits when used over a path with capable transport can offer benefits when used over a path with
equipment that implements an AQM method with CE marking of IP equipment that implements an AQM method with CE marking of IP
packets [RFC8087], since it can react to congestion without also packets [RFC8087], since it can react to congestion without also
having to recover from lost packets. having to recover from lost packets.
ECN exposes the presence of congestion. The reception of CE- ECN exposes the presence of congestion. The reception of CE-
marked packets can be used to estimate the level of incipient marked packets can be used to estimate the level of incipient
congestion on the upstream portion of the path from the point of congestion on the upstream portion of the path from the point of
observation (Section 2.5 of [RFC8087]). Interpreting the marking observation (Section 2.5 of [RFC8087]). Interpreting the marking
behaviour (i.e., assessing congestion and diagnosing faults) behaviour (i.e., assessing congestion and diagnosing faults)
requires context from the transport layer, such as path RTT. requires context from the transport layer, such as path RTT.
AQM and ECN offer a range of algorithms and configuration options. AQM and ECN offer a range of algorithms and configuration options.
Tools therefore need to be available to network operators and Tools therefore have to be available to network operators and
researchers to understand the implication of configuration choices researchers to understand the implication of configuration choices
and transport behaviour as the use of ECN increases and new and transport behaviour as the use of ECN increases and new
methods emerge [RFC7567]. methods emerge [RFC7567].
When transport headers are concealed, operators will be unable to use When transport headers cannot be observed, operators are unable to
this information directly. Careful use of the network layer features use this information directly. Careful use of the network layer
can help address provide similar information in the case where the features can help provide similar information in the case where the
network is unable to inspect transport protocol headers. network is unable to inspect transport protocol headers.
Section Section 5 describes use of network extension headers. Section Section 5 describes use of network extension headers.
3.2. Transport Measurement 3.2. Transport Measurement
The common language between network operators and application/content The common language between network operators and application/content
providers/users is packet transfer performance at a layer that all providers/users is packet transfer performance at a layer that all
can view and analyse. For most packets, this has been the transport can view and analyse. For most packets, this has been the transport
layer, until the emergence of transport protocols performing header layer, until the emergence of transport protocols performing header
encryption, with the obvious exception of VPNs and IPsec. encryption, with the obvious exception of VPNs and IPsec.
When encryption conceals more layers in each packet, people seeking When encryption hides more layers in each packet, people seeking
understanding of the network operation rely more on pattern inference understanding of the network operation rely more on pattern inference
and other heuristics. It remains to be seen whether more complex and other heuristics. It remains to be seen whether more complex
inferences can be mastered to produce the same monitoring accuracy inferences can be mastered to produce the same monitoring accuracy
(see section 2.1.1 of [RFC8404]). (see section 2.1.1 of [RFC8404]).
When measurement datasets are made available by servers or client When measurement datasets are made available by servers or client
endpoints, additional metadata, such as the state of the network, is endpoints, additional metadata, such as the state of the network, is
often necessary to interpret this data to answer questions about often necessary to interpret this data to answer questions about
network performance or understand a pathology. Collecting and network performance or understand a pathology. Collecting and
coordinating such metadata is more difficult when the observation coordinating such metadata is more difficult when the observation
skipping to change at page 18, line 44 skipping to change at page 19, line 28
common network device, interface port, etc. A simple example is common network device, interface port, etc. A simple example is
monitoring of a network device that uses a scheduler or active queue monitoring of a network device that uses a scheduler or active queue
management technique [RFC7567], where it could be desirable to management technique [RFC7567], where it could be desirable to
understand whether the algorithms are correctly controlling latency, understand whether the algorithms are correctly controlling latency,
or if overload protection is working. This understanding implies or if overload protection is working. This understanding implies
knowledge of how traffic is assigned to any sub-queues used for flow knowledge of how traffic is assigned to any sub-queues used for flow
scheduling, but can also require information about how the traffic scheduling, but can also require information about how the traffic
dynamics impact active queue management, starvation prevention dynamics impact active queue management, starvation prevention
mechanisms, and circuit-breakers. mechanisms, and circuit-breakers.
Sometimes multiple on-path observation points are needed. By Sometimes multiple on-path observation points have to be used. By
correlating observations of headers at multiple points along the path correlating observations of headers at multiple points along the path
(e.g., at the ingress and egress of a network segment), an observer (e.g., at the ingress and egress of a network segment), an observer
can determine the contribution of a portion of the path to an can determine the contribution of a portion of the path to an
observed metric, to locate a source of delay, jitter, loss, observed metric, to locate a source of delay, jitter, loss,
reordering, congestion marking, etc. reordering, congestion marking, etc.
3.2.2. Use by Operators to Plan and Provision Networks 3.2.2. Use by Operators to Plan and Provision Networks
Traffic measurements are used by operators to help plan deployment of Traffic rate and volume measurements are used by operators to help
new equipment and configuration in their networks. Data is also plan deployment of new equipment and configuration in their networks.
valuable to equipment vendors who want to understand traffic trends Data is also valuable to equipment vendors who want to understand
and patterns of usage as inputs to decisions about planning products traffic trends and patterns of usage as inputs to decisions about
and provisioning for new deployments. This measurement information planning products and provisioning for new deployments. This
can also be correlated with billing information when this is also measurement information can also be correlated with billing
collected by an operator. information when this is also collected by an operator.
A network operator supporting traffic that uses transport header
encryption might not have access to per-flow measurement data.
Trends in aggregate traffic can be observed and can be related to the Trends in aggregate traffic can be observed and can be related to the
endpoint addresses being used, but it might be impossible to endpoint addresses being used, but when transport information is not
correlate patterns in measurements with changes in transport observable, it might be impossible to correlate patterns in
protocols (e.g., the impact of changes in introducing a new transport measurements with changes in transport protocols. This increases the
protocol mechanism). This increases the dependency on other indirect dependency on other indirect sources of information to inform
sources of information to inform planning and provisioning. planning and provisioning.
3.2.3. Service Performance Measurement 3.2.3. Service Performance Measurement
Traffic measurements (e.g., traffic volume, loss, latency) can be Performance measurements (e.g., throughput, loss, latency) can be
used by various actors to help analyse the performance offered to the used by various actors to analyse the service offered to the users of
users of a network segment, and to inform operational practice. a network segment, and to inform operational practice.
While active measurements (see section 3.4 of [RFC7799]) could be
used within a network, passive measurements (see section 3.6 of
[RFC7799]) can have advantages in terms of eliminating unproductive
test traffic, reducing the influence of test traffic on the overall
traffic mix, and the ability to choose the point of observation (see
Section 3.2.1). Passive measurements can rely on observing transport
headers, which is not possible if those headers are encrypted, but
could utilise information about traffic volumes or patterns of
interaction to deduce metrics.
3.2.4. Measuring Transport to Support Network Operations 3.2.4. Measuring Transport to Support Network Operations
Information provided by tools observing transport headers can help The traffic that can be observed by on-path network devices (the
determine whether mechanisms are needed in the network to prevent "wire image") is a function of transport protocol design/options,
flows from acquiring excessive network capacity. Operators can network use, applications, and user characteristics. In general,
implement operational practices to manage traffic flows (e.g., under when only a small proportion of the traffic has a specific
severe congestion) by deploying rate-limiters, traffic shaping or (different) characteristic, such traffic seldom leads to operational
network transport circuit breakers [RFC8084]. concern, although the ability to measure and monitor it is less. The
desire to understand the traffic and protocol interactions typically
grows as the proportion of traffic increases in volume. The
challenges increase when multiple instances of an evolving protocol
contribute to the traffic that share network capacity.
Operators can manage traffic load (e.g., when the network is severely
overloaded) by deploying rate-limiters, traffic shaping, or network
transport circuit breakers [RFC8084]. The information provided by
observing transport headers is a source of data that can help to
inform such mechanisms.
Congestion Control Compliance of Traffic: Congestion control is a Congestion Control Compliance of Traffic: Congestion control is a
key transport function [RFC2914]. Many network operators key transport function [RFC2914]. Many network operators
implicitly accept that TCP traffic complies with a behaviour that implicitly accept that TCP traffic complies with a behaviour that
is acceptable for use in the shared Internet. TCP algorithms have is acceptable for the shared Internet. TCP algorithms have been
been continuously improved over decades and they have reached a continuously improved over decades, and have reached a level of
level of efficiency and correctness that custom application-layer efficiency and correctness that is difficult to match in custom
mechanisms will struggle to easily duplicate [RFC8085]. application-layer mechanisms [RFC8085].
A standards-compliant TCP stack provides congestion control that A standards-compliant TCP stack provides congestion control that
is judged safe for use across the Internet. Applications is judged safe for use across the Internet. Applications
developed on top of well-designed transports can be expected to developed on top of well-designed transports can be expected to
appropriately control their network usage, reacting when the appropriately control their network usage, reacting when the
network experiences congestion, by back-off and reduce the load network experiences congestion, by back-off and reduce the load
placed on the network. This is the normal expected behaviour for placed on the network. This is the normal expected behaviour for
IETF-specified transports (e.g., TCP and SCTP). IETF-specified transports (e.g., TCP and SCTP).
However, when anomalies are detected, tools can interpret the However, when anomalies are detected, tools can interpret the
transport protocol header information to help understand the transport protocol header information to help understand the
impact of specific transport protocols (or protocol mechanisms) on impact of specific transport protocols (or protocol mechanisms) on
the other traffic that shares a network. An observation in the the other traffic that shares a network. An observation in the
network can gain an understanding of the dynamics of a flow and network can gain an understanding of the dynamics of a flow and
its congestion control behaviour. Analysing observed flows can its congestion control behaviour. Analysing observed flows can
help to build confidence that an application flow backs-off its help to build confidence that an application flow backs-off its
share of the network load in the face of persistent congestion, share of the network load under persistent congestion, and hence
and hence to understand whether the behaviour is appropriate for to understand whether the behaviour is appropriate for sharing
sharing limited network capacity. For example, it is common to limited network capacity. For example, it is common to visualise
visualise plots of TCP sequence numbers versus time for a flow to plots of TCP sequence numbers versus time for a flow to understand
understand how a flow shares available capacity, deduce its how a flow shares available capacity, deduce its dynamics in
dynamics in response to congestion, etc. response to congestion, etc.
The ability to identify sources that contribute to persistent The ability to identify sources that contribute to persistent
congestion is important to the safe operation of network congestion is important to the safe operation of network
infrastructure, and can inform configuration of network devices to infrastructure, and can inform configuration of network devices to
complement the endpoint congestion avoidance mechanisms [RFC7567] complement the endpoint congestion avoidance mechanisms [RFC7567]
[RFC8084] to avoid a portion of the network being driven into [RFC8084] to avoid a portion of the network being driven into
congestion collapse [RFC2914]. congestion collapse [RFC2914].
Congestion Control Compliance for UDP traffic: UDP provides a Congestion Control Compliance for UDP traffic: UDP provides a
minimal message-passing datagram transport that has no inherent minimal message-passing datagram transport that has no inherent
congestion control mechanisms. Because congestion control is congestion control mechanisms. Because congestion control is
critical to the stable operation of the Internet, applications and critical to the stable operation of the Internet, applications and
other protocols that choose to use UDP as a transport need to other protocols that choose to use UDP as a transport have to
employ mechanisms to prevent collapse, avoid unacceptable employ mechanisms to prevent collapse, avoid unacceptable
contributions to jitter/latency, and to establish an acceptable contributions to jitter/latency, and to establish an acceptable
share of capacity with concurrent traffic [RFC8085]. share of capacity with concurrent traffic [RFC8085].
A network operator needs tools to understand if datagram flows A network operator can observe the headers of transport protocols
(e.g., using UDP) comply with congestion control expectations and layered above UDP to understand if the datagram flows comply with
therefore whether there is a need to deploy methods such as rate- congestion control expectations. This can help inform a decision
limiters, transport circuit breakers, or other methods to enforce on whether it might be appropriate to deploy methods such as rate-
acceptable usage for the offered service. limiters to enforce acceptable usage.
UDP flows that expose a well-known header by specifying the format UDP flows that expose a well-known header can be observed to gain
of header fields can allow information to be observed to gain
understanding of the dynamics of a flow and its congestion control understanding of the dynamics of a flow and its congestion control
behaviour. For example, tools exist to monitor various aspects of behaviour. For example, tools exist to monitor various aspects of
RTP and RTCP header information for real-time flows (see RTP header information and RTCP reports for real-time flows (see
Section 3.1.2). The Secure RTP extensions [RFC3711] were Section 3.1.2). The Secure RTP and RTCP extensions [RFC3711] were
explicitly designed to expose some header information to enable explicitly designed to expose some header information to enable
such observation, while protecting the payload data. such observation, while protecting the payload data.
3.3. Use for Network Diagnostics and Troubleshooting 3.3. Use for Network Diagnostics and Troubleshooting
Transport header information can be useful for a variety of Transport header information can be utilised for a variety of
operational tasks [RFC8404]: to diagnose network problems, assess operational tasks [RFC8404]: to diagnose network problems, assess
network provider performance, evaluate equipment/protocol network provider performance, evaluate equipment or protocol
performance, capacity planning, management of security threats performance, capacity planning, management of security threats
(including denial of service), and responding to user performance (including denial of service), and responding to user performance
questions. Section 3.1.2 and Section 5 of [RFC8404] provide further questions. Section 3.1.2 and Section 5 of [RFC8404] provide further
examples. These tasks seldom involve the need to determine the examples.
contents of the transport payload, or other application details. The
use of payload encryption has the desirable effect of preventing
unintended observation of the user data.
A network operator supporting traffic that uses transport header
encryption can see only encrypted transport headers. This prevents
deployment of performance measurement tools that rely on transport
protocol information. Choosing to encrypt all the information
reduces the ability of an operator to observe transport performance
and could limit the ability of network operators to trace problems,
make appropriate QoS decisions, or response to other queries about
the network service. For some this will be blessing, for others it
might be a curse. For example, operational performance data about
encrypted flows needs to be determined by traffic pattern analysis,
rather than relying on traditional tools. This can impact the
ability of the operator to respond to faults, it could require
reliance on endpoint diagnostic tools or user involvement in
diagnosing and troubleshooting unusual use cases or non-trivial
problems. A key need here is for tools to provide useful information
during network anomalies (e.g., significant reordering, high or
intermittent loss).
Measurements can be used to monitor the health of a portion of the
Internet, to provide early warning of the need to take action. They
can assist in setting buffer sizes, debugging and diagnosing the root
causes of faults that concern a particular user's traffic. They can
also be used to support post-mortem investigation after an anomaly to
determine the root cause of a problem.
In some cases, measurements could involve active injection of test Operators can monitor the health of a portion of the Internet, to
traffic to perform a measurement. However, most operators do not provide early warning and trigger action. Traffic and performance
have access to user equipment, therefore the point of test is measurements can assist in setting buffer sizes, debugging and
normally different from the transport endpoint. Injection of test diagnosing the root causes of faults that concern a particular user's
traffic can incur an additional cost in running such tests (e.g., the traffic. They can also be used to support post-mortem investigation
implications of capacity tests in a mobile network are obvious). after an anomaly to determine the root cause of a problem.
Some active measurements [RFC7799] (e.g., response under load or
particular workloads) perturb other traffic, and could require
dedicated access to the network segment. An alternative approach is
to use in-network techniques that observe transport packet headers
added while traffic traverses an operational network to make the
measurements. These measurements do not require the cooperation of
an endpoint.
In other cases, measurement involves dissecting network traffic In other cases, measurement involves dissecting network traffic
flows. The observed transport layer information can help identify flows. Observed transport header information can help identify
whether the link/network tuning is effective and alert to potential whether link/network tuning is effective and alert to potential
problems that can be hard to derive from link or device measurements problems that can be hard to derive from link or device measurements
alone. The design trade-offs for radio networks are often very alone.
different from those of wired networks. A radio-based network (e.g.,
cellular mobile, enterprise WiFi, satellite access/back-haul, point-
to-point radio) has the complexity of a subsystem that performs radio
resource management, with direct impact on the available capacity,
and potentially loss/reordering of packets. The impact of the
pattern of loss and congestion, differs for different traffic types,
correlation with propagation and interference can all have
significant impact on the cost and performance of a provided service.
The need for this type of information is expected to increase as
operators bring together heterogeneous types of network equipment and
seek to deploy opportunistic methods to access radio spectrum.
A flow that conceals its transport header information could imply An alternative could rely on access to endpoint diagnostic tools or
"don't touch" to some operators. This could limit a trouble-shooting user involvement in diagnosing and troubleshooting unusual use cases
response to "can't help, no trouble found". or to troubleshoot non-trivial problems.
Another approach is to use traffic pattern analysis. Such tools can
provide useful information during network anomalies (e.g., detecting
significant reordering, high or intermittent loss), however indirect
measurements would need to be carefully designed to provide reliable
signals for diagnostics and troubleshooting.
The design trade-offs for radio networks are often very different
from those of wired networks. A radio-based network (e.g., cellular
mobile, enterprise WiFi, satellite access/back-haul, point-to-point
radio) has the complexity of a subsystem that performs radio resource
management, with direct impact on the available capacity, and
potentially loss/reordering of packets. The impact of the pattern of
loss and congestion, differs for different traffic types, correlation
with propagation and interference can all have significant impact on
the cost and performance of a provided service. For radio links, the
use for this type of information is expected to increase as operators
bring together heterogeneous types of network equipment and seek to
deploy opportunistic methods to access radio spectrum.
Lack of tools and resulting information can reduce the ability of an
operator to observe transport performance and could limit the ability
of network operators to trace problems, make appropriate QoS
decisions, or respond to other queries about the network service.
A network operator supporting traffic that uses transport header
encryption is unable to use tools that rely on transport protocol
information. However, the use of encryption has the desirable effect
of preventing unintended observation of the payload data and these
tools seldom seek to observe the payload, or other application
details. A flow that hides its transport header information could
imply "don't touch" to some operators. This might limit a trouble-
shooting response to "can't help, no trouble found".
3.4. Header Compression 3.4. Header Compression
Header compression saves link capacity by compressing network and Header compression saves link capacity by compressing network and
transport protocol headers on a per-hop basis. It was widely used transport protocol headers on a per-hop basis. It was widely used
with low bandwidth dial-up access links, and still finds application with low bandwidth dial-up access links, and still finds application
on wireless links that are subject to capacity constraints. Header on wireless links that are subject to capacity constraints. Header
compression has been specified for use with TCP/IP and RTP/UDP/IP compression has been specified for use with TCP/IP and RTP/UDP/IP
flows [RFC2507], [RFC2508], [RFC4995]. flows [RFC2507], [RFC2508], [RFC4995].
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network layer headers, with a significant reduction in efficiency. network layer headers, with a significant reduction in efficiency.
4. Encryption and Authentication of Transport Headers 4. Encryption and Authentication of Transport Headers
End-to-end encryption can be applied at various protocol layers. It End-to-end encryption can be applied at various protocol layers. It
can be applied above the transport to encrypt the transport payload can be applied above the transport to encrypt the transport payload
(e.g., using TLS). This can hide information from an eavesdropper in (e.g., using TLS). This can hide information from an eavesdropper in
the network. It can also help protect the privacy of a user, by the network. It can also help protect the privacy of a user, by
hiding data relating to user/device identity or location. hiding data relating to user/device identity or location.
4.1. Motivation
There are several motivations for encryption: There are several motivations for encryption:
o One motive to use encryption is a response to perceptions that the o One motive to encrypt transport headers is in response to
network has become ossified by over-reliance on middleboxes that perceptions that the network has become ossified, since traffic
prevent new protocols and mechanisms from being deployed. This inspecting middleboxes prevent new protocols and mechanisms from
has lead to a perception that there is too much "manipulation" of being deployed. This has lead to a perception that there is too
protocol headers within the network, and that designing to deploy much "manipulation" of protocol headers within the network, and
in such networks is preventing transport evolution. In the light that designing to deploy in such networks is preventing transport
of this, a method that authenticates transport headers could help evolution. One benefit of encrypting transport headers is that it
improve the pace of transport development, by eliminating the need can help improve the pace of transport development by eliminating
to always consider deployed middleboxes interference by deployed middleboxes.
[I-D.trammell-plus-abstract-mech], or potentially to only
explicitly enable use by middleboxes for particular paths with
particular middleboxes that are deliberately deployed to realise a
useful function for the network and/or users[RFC3135].
o Another motivation stems from increased concerns about privacy and o Another motivation stems from increased concerns about privacy and
surveillance. Some Internet users have valued the ability to surveillance. Users value the ability to protect their identity
protect identity, user location, and defend against traffic and location, and defend against traffic analysis. Revelations
analysis, and have used methods such as IPsec Encapsulated about the use of pervasive surveillance [RFC7624] have, to some
Security Payload (ESP), VPNs and other encrypted tunnel extent, eroded trust in the service offered by network operators
technologies. Revelations about the use of pervasive surveillance and have led to an increased use of encryption to avoid unwanted
[RFC7624] have, to some extent, eroded trust in the service eavesdropping on communications. Concerns have also been voiced
offered by network operators, and following the Snowden about the addition of information to packets by third parties to
revelations in the USA in 2013 has led to an increased desire for provide analytics, customization, advertising, cross-site tracking
people to employ encryption to avoid unwanted "eavesdropping" on of users, to bill the customer, or to selectively allow or block
their communications. Concerns have also been voiced about the content. Whatever the reasons, the IETF is designing protocols
addition of information to packets by third parties to provide that include transport header encryption (e.g., QUIC
analytics, customization, advertising, cross-site tracking of
users, to bill the customer, or to selectively allow or block
content. Whatever the reasons, the IETF is designing new
protocols that include transport header encryption (e.g., QUIC
[I-D.ietf-quic-transport]) to supplement the already widespread [I-D.ietf-quic-transport]) to supplement the already widespread
payload encryption. payload encryption, and to further limit exposure of transport
metadata to the network.
o Any header information that has a clear definition in the protocol
message format(s), or is implied by that definition, and is not
cryptographically confidentiality-protected can be unambiguously
interpreted by on-path observers [RFC8546].
Encryption methods do not prevent traffic analysis, and usage needs The use of transport header authentication and encryption exposes a
to reflect that profiling of users, identification of location, and tussle between middlebox vendors, operators, applications developers
fingerprinting of behaviour can take place even on encrypted traffic and users:
flows. The use of transport layer authentication and encryption
exposes a tussle between middlebox vendors, operators, applications
developers and users:
o On the one hand, future Internet protocols that enable large-scale o On the one hand, future Internet protocols that support transport
encryption assist in the restoration of the end-to-end nature of header encryption assist in the restoration of the end-to-end
the Internet by returning complex processing to the endpoints, nature of the Internet by returning complex processing to the
since middleboxes cannot modify what they cannot see. endpoints, since middleboxes cannot modify what they cannot see,
and can improve privacy by reducing leakage of transport metadata.
o On the other hand, encryption of transport layer header o On the other hand, encryption of transport layer header
information has implications for people who are responsible for information has implications for people who are responsible for
operating networks and researchers and analysts seeking to operating networks, and researchers and analysts seeking to
understand the dynamics of protocols and traffic patterns. understand the dynamics of protocols and traffic patterns.
Whatever the motives, a decision to use pervasive transport header A decision to use transport header encryption can improve user
encryption will have implications on the way in which design and privacy, and can reduce protocol ossification and help the evolution
evaluation is performed. This can, in turn, impact the direction of of the transport protocol stack, but is also has implications for
evolution of the transport protocol stack. While the IETF can network operations and management.
specify protocols, the success in actual deployment is often
determined by many factors [RFC5218] that are not always clear at the 4.2. Approaches to Transport Header Protection
time when protocols are being defined.
The following briefly reviews some security design options for The following briefly reviews some security design options for
transport protocols. A Survey of Transport Security Protocols transport protocols. A Survey of Transport Security Protocols
[I-D.ietf-taps-transport-security] provides more details concerning [I-D.ietf-taps-transport-security] provides more details concerning
commonly used encryption methods at the transport layer. commonly used encryption methods at the transport layer.
Authenticating the Transport Protocol Header: Transport layer header Authenticating the Transport Protocol Header: Transport layer header
information can be authenticated. An integrity check that information can be authenticated. An integrity check that
protects the immutable transport header fields, but can still protects the immutable transport header fields, but can still
expose the transport protocol header information in the clear, expose the transport protocol header information in the clear,
skipping to change at page 26, line 6 skipping to change at page 26, line 12
considers only immutable fields in the transport headers, that is, considers only immutable fields in the transport headers, that is,
fields that can be authenticated End-to-End across a path. fields that can be authenticated End-to-End across a path.
An example of a method that encrypts some, but not all, transport An example of a method that encrypts some, but not all, transport
information is GRE-in-UDP [RFC8086] when used with GRE encryption. information is GRE-in-UDP [RFC8086] when used with GRE encryption.
Optional Encryption of Header Information: There are implications to Optional Encryption of Header Information: There are implications to
the use of optional header encryption in the design of a transport the use of optional header encryption in the design of a transport
protocol, where support of optional mechanisms can increase the protocol, where support of optional mechanisms can increase the
complexity of the protocol and its implementation, and in the complexity of the protocol and its implementation, and in the
management decisions that are needed to use variable format management decisions that are have to be made to use variable
fields. Instead, fields of a specific type ought to always be format fields. Instead, fields of a specific type ought to always
sent with the same level of confidentiality or integrity be sent with the same level of confidentiality or integrity
protection. protection.
As seen, different transports use encryption to protect their header As seen, different transports use encryption to protect their header
information to varying degrees. There is, however, a trend towards information to varying degrees. The trend is towards increased
increased protection with newer transport protocols. protection.
5. Addition of Transport Information to Network-Layer Headers 5. Addition of Transport Information to Network-Layer Headers
An on-path device can make measurements by utilising additional An on-path device can make measurements by utilising additional
protocol headers carrying operations, administration and management protocol headers carrying operations, administration and management
(OAM) information in an additional packet header. Using network- (OAM) information in an additional packet header. Using network-
layer approaches to reveal information has the potential that the layer approaches to reveal information has the potential that the
same method (and hence same observation and analysis tools) can be same method (and hence same observation and analysis tools) can be
consistently used by multiple transport protocols [RFC8558]. There consistently used by multiple transport protocols [RFC8558]. There
could also be less desirable implications of separating the operation could also be less desirable implications of separating the operation
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extension header or an IPv4 option. This information can be used extension header or an IPv4 option. This information can be used
across multiple network segments, or between the transport endpoints. across multiple network segments, or between the transport endpoints.
One example is the IPv6 Performance and Diagnostic Metrics (PDM) One example is the IPv6 Performance and Diagnostic Metrics (PDM)
Destination Option [RFC8250]. This allows a sender to optionally Destination Option [RFC8250]. This allows a sender to optionally
include a destination option that caries header fields that can be include a destination option that caries header fields that can be
used to observe timestamps and packet sequence numbers. This used to observe timestamps and packet sequence numbers. This
information could be authenticated by receiving transport endpoints information could be authenticated by receiving transport endpoints
when the information is added at the sender and visible at the when the information is added at the sender and visible at the
receiving endpoint, although methods to do this have not currently receiving endpoint, although methods to do this have not currently
been proposed. This method needs to be explicitly enabled at the been proposed. This method has to be explicitly enabled at the
sender. sender.
Current measurement results suggest that it could currently be Current measurement results suggest that it could currently be
undesirable to rely on methods requiring end to end support of undesirable to rely on methods requiring end-to-end support of
network options or extension headers across the Internet. IPv4 network options or extension headers across the Internet. IPv4
network options are often not supported (or are carried on a slower network options are often not supported (or are carried on a slower
processing path) and some IPv6 networks have been observed to drop processing path) and some IPv6 networks have been observed to drop
packets that set an IPv6 header extension (e.g., results from 2016 in packets that set an IPv6 header extension (e.g., results from 2016 in
[RFC7872]). [RFC7872]).
Another potential issue is that protocols that separately expose Protocols can be designed to expose header information separately to
header information do not necessarily have an incentive to expose the the (hidden) fields used by the protocol state machine. On the one
actual information that is utilised by the protocol itself and could hand, such approaches can simplify tools by exposing the relevant
metrics (loss, latency, etc), rather having to derive this from other
fields. This also permits the protocol to evolve independently of
the ossified observable header [RFC8558]. On the other hand,
protocols do not necessarily have an incentive to expose the actual
information that is utilised by the protocol itself and could
therefore manipulate the exposed header information to gain an therefore manipulate the exposed header information to gain an
advantage from the network. Where the information is provided by an advantage from the network. Where the information is provided by an
endpoint, the incentive to reflect actual transport information needs endpoint, the incentive to reflect actual transport information has
to be considered when proposing a method. to be considered when proposing a method.
6. Implications of Protecting the Transport Headers 6. Implications of Protecting the Transport Headers
The choice of which fields to expose and which to encrypt is a design The choice of which transport header fields to expose and which to
choice for the transport protocol. Any selective encryption method encrypt is a design decision for the transport protocol. Selective
requires trading two conflicting goals for a transport protocol encryption requires trading conflicting goals of observability and
designer to decide which header fields to encrypt. Security work network support, privacy, and risk of ossification, to decide what
typically employs a design technique that seeks to expose only what header fields to protect and which to make visible.
is needed. This approach provides incentives to not reveal any
information that is not necessary for the end-to-end communication. Security work typically employs a design technique that seeks to
However, there can be performance and operational benefits in expose only what is needed. This approach provides incentives to not
exposing selected information to network tools. reveal any information that is not necessary for the end-to-end
communication. However, there can be performance and operational
benefits in exposing selected information to network tools.
This section explores key implications of working with encrypted This section explores key implications of working with encrypted
transport protocols. transport protocols.
6.1. Independent Measurement 6.1. Independent Measurement
Independent observation by multiple actors is important if the Independent observation by multiple actors is important if the
transport community is to maintain an accurate understanding of the transport community is to maintain an accurate understanding of the
network. Encrypting transport header encryption changes the ability network. Encrypting transport header encryption changes the ability
to collect and independently analyse data. Internet transport to collect and independently analyse data. Internet transport
protocols employ a set of mechanisms. Some of these need to work in protocols employ a set of mechanisms. Some of these have to work in
cooperation with the network layer for loss detection and recovery, cooperation with the network layer for loss detection and recovery,
congestion detection and control. Others need to work only end-to- congestion detection and control. Others have to work only end-to-
end (e.g., parameter negotiation, flow-control). end (e.g., parameter negotiation, flow-control).
The majority of present Internet applications use two well-known The majority of present Internet applications use two well-known
transport protocols, TCP and UDP. Although TCP represents the transport protocols, TCP and UDP. Although TCP represents the
majority of current traffic, many real-time applications use UDP, and majority of current traffic, many real-time applications use UDP, and
much of this traffic utilises RTP format headers in the payload of much of this traffic utilises RTP format headers in the payload of
the UDP datagram. Since these protocol headers have been fixed for the UDP datagram. Since these protocol headers have been fixed for
decades, a range of tools and analysis methods have became common and decades, a range of tools and analysis methods have became common and
well-understood. well-understood.
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when TCP is used over an unencrypted network path (i.e., one that when TCP is used over an unencrypted network path (i.e., one that
does not use IPsec or other encryption below the transport), it does not use IPsec or other encryption below the transport), it
implicitly exposes header information that can be used for implicitly exposes header information that can be used for
measurement at any point along the path. This information is measurement at any point along the path. This information is
necessary for the protocol's correct operation, therefore there is no necessary for the protocol's correct operation, therefore there is no
incentive for a TCP or RTP implementation to put incorrect incentive for a TCP or RTP implementation to put incorrect
information in this transport header. A network device can have information in this transport header. A network device can have
confidence that the well-known (and ossified) transport information confidence that the well-known (and ossified) transport information
represents the actual state of the endpoints. represents the actual state of the endpoints.
When encryption is used to conceal some or all of the transport When encryption is used to hide some or all of the transport headers,
headers, the transport protocol chooses which information to reveal the transport protocol chooses which information to reveal to the
to the network about its internal state, what information to leave network about its internal state, what information to leave
encrypted, and what fields to grease to protect against future encrypted, and what fields to grease to protect against future
ossification. Such a transport could be designed, for example, to ossification. Such a transport could be designed, for example, to
provide summary data regarding its performance, congestion control provide summary data regarding its performance, congestion control
state, etc., or to make an explicit measurement signal available. state, etc., or to make an explicit measurement signal available.
For example, a QUIC endpoint can optionally set the spin bit to For example, a QUIC endpoint can optionally set the spin bit to
reflect to explicitly reveal the RTT of an encrypted transport reflect to explicitly reveal the RTT of an encrypted transport
session to the on-path network devices [I-D.ietf-quic-transport]). session to the on-path network devices [I-D.ietf-quic-transport]).
When providing or using such information, it becomes important to When providing or using such information, it is important to consider
consider the privacy of the user and their incentive for providing the privacy of the user and their incentive for providing accurate
accurate and detailed information. Protocols that selectively reveal and detailed information. Protocols that selectively reveal some
some transport state or measurement signals are choosing to establish transport state or measurement signals are choosing to establish a
a trust relationship with the network operators. There is no trust relationship with the network operators. There is no protocol
protocol mechanism that can guarantee that the information provided mechanism that can guarantee that the information provided represents
represents the actual transport state of the endpoints, since those the actual transport state of the endpoints, since those endpoints
endpoints can always send additional information in the encrypted can always send additional information in the encrypted part of the
part of the header, to update or replace whatever they reveal. This header, to update or replace whatever they reveal. This reduces the
reduces the ability to independently measure and verify that a ability to independently measure and verify that a protocol is
protocol is behaving as expected. Some operational uses need the behaving as expected. For some operational uses, the information has
information to contain sufficient detail to understand, and possibly to contain sufficient detail to understand, and possibly reconstruct,
reconstruct, the network traffic pattern for further testing; such the network traffic pattern for further testing. In this case,
operators need to gain the trust of transport protocol implementers operators have to gain the trust of transport protocol implementers
if they are to correctly reveal such information. if the transport headers are to correctly reveal such information.
Operations, Administration, and Maintenance (OAM) data records Operations, Administration, and Maintenance (OAM) data records
[I-D.ietf-ippm-ioam-data] could be embedded into a variety of [I-D.ietf-ippm-ioam-data] could be embedded into a variety of
encapsulation methods at different layers to support the goals of a encapsulation methods at different layers to support the goals of a
specific operational domain. OAM-related metadata can support specific operational domain. OAM-related metadata can support
functions such as performance evaluation, path-tracing, path functions such as performance evaluation, path-tracing, path
verification information, classification and a diversity of other verification information, classification and a diversity of other
uses. When encryption is used to conceal some or all of the uses. When encryption is used to hide some or all of the transport
transport headers, analysis will require coordination between actors headers, analysis requires coordination between actors at different
at different layers to successfully characterise flows and correlate layers to successfully characterise flows and correlate the
the performance or behaviour of a specific mechanism with the performance or behaviour of a specific mechanism with the
configuration and traffic using operational equipment (e.g., configuration and traffic using operational equipment (e.g.,
combining transport and network measurements to explore congestion combining transport and network measurements to explore congestion
control dynamics, the implications of designs for active queue control dynamics, the implications of designs for active queue
management or circuit breakers). management or circuit breakers).
Some measurements could be completed by utilising a standardised Some measurements could be completed by utilising endpoint-based
endpoint-based logging format (e.g., based on Quic-Trace logging (e.g., based on Quic-Trace [Quic-Trace]). Such information
[Quic-Trace]). Such information will have a diversity of uses, has a diversity of uses, including developers wishing to debug/
including developers wishing to debug/understand the transport/ understand the transport/application protocols with which they work,
application protocols with which they work, researchers seeking to researchers seeking to spot trends and anomalies, and to characterise
spot trends and anomalies, and to characterise variants of protocols. variants of protocols. A standard format for endpoint logging could
Logs collected at endpoints could be shared (after appropriate allow these to be shared (after appropriate anonymisation) to
annoymisation) to help understand performance and pathologies. understand performance and pathologies. Measurements based on
Measurements based on logging will need to establish the validity and logging have to establish the validity and provenance of the logged
provenance of the logged information to establish how and when traces information to establish how and when traces were captured.
were captured.
However, endpoint logs do not provide equivalent information to in- Despite being applicable in some scenarios, endpoint logs do not
network measurements. In particular, endpoint logs contain only a provide equivalent information to in-network measurements. In
part of the information needed to understand the operation of network particular, endpoint logs contain only a part of the information to
devices and identify issues such as link performance or capacity understand the operation of network devices and identify issues such
sharing between multiple flows. Additional information is needed to as link performance or capacity sharing between multiple flows.
determine which equipment/links are used and the configuration of Additional information has to be combined to determine which
equipment along the network paths being measured. equipment/links are used and the configuration of equipment along the
network paths being measured.
6.2. Characterising "Unknown" Network Traffic 6.2. Characterising "Unknown" Network Traffic
The patterns and types of traffic that share Internet capacity change The patterns and types of traffic that share Internet capacity change
over time as networked applications, usage patterns and protocols over time as networked applications, usage patterns and protocols
continue to evolve. continue to evolve.
If "unknown" or "uncharacterised" traffic patterns form a small part If "unknown" or "uncharacterised" traffic patterns form a small part
of the traffic aggregate passing through a network device or segment of the traffic aggregate passing through a network device or segment
of the network the path, the dynamics of the uncharacterised traffic of the network the path, the dynamics of the uncharacterised traffic
might not have a significant collateral impact on the performance of might not have a significant collateral impact on the performance of
other traffic that shares this network segment. Once the proportion other traffic that shares this network segment. Once the proportion
of this traffic increases, the need to monitor the traffic and of this traffic increases, monitoring the traffic can determine if
determine if appropriate safety measures need to be put in place. appropriate safety measures have to be put in place.
Tracking the impact of new mechanisms and protocols requires traffic Tracking the impact of new mechanisms and protocols requires traffic
volume to be measured and new transport behaviours to be identified. volume to be measured and new transport behaviours to be identified.
This is especially true of protocols operating over a UDP substrate. This is especially true of protocols operating over a UDP substrate.
The level and style of encryption needs to be considered in The level and style of encryption has to be considered in determining
determining how this activity is performed. On a shorter timescale, how this activity is performed. On a shorter timescale, information
information could also need to be collected to manage denial of could also have to be collected to manage denial of service attacks
service attacks against the infrastructure. against the infrastructure.
6.3. Accountability and Internet Transport Protocols 6.3. Accountability and Internet Transport Protocols
Information provided by tools observing transport headers can be used Information provided by tools observing transport headers can be used
to classify traffic, and to limit the network capacity used by to classify traffic, and to limit the network capacity used by
certain flows, as discussed in Section 3.2.4). Equally, operators certain flows, as discussed in Section 3.2.4). Equally, operators
could use analysis of transport headers and transport flow state to could use analysis of transport headers and transport flow state to
demonstrate that they are not providing differential treatment to demonstrate that they are not providing differential treatment to
certain flows. Obfuscating or hiding this information using certain flows. Obfuscating or hiding this information using
encryption could lead operators and maintainers of middleboxes encryption could lead operators and maintainers of middleboxes
(firewalls, etc.) to seek other methods to classify, and potentially (firewalls, etc.) to seek other methods to classify, and potentially
other mechanisms to condition, network traffic. other mechanisms to condition, network traffic.
A lack of data that reduces the level of precision with which flows A lack of data that reduces the level of precision with which flows
can be classified also reduces the design space for conditioning can be classified also reduces the design space for conditioning
mechanisms (e.g., rate limiting, circuit breaker techniques mechanisms (e.g., rate limiting, circuit breaker techniques
[RFC8084], or blocking of uncharacterised traffic), and this needs to [RFC8084], or blocking of uncharacterised traffic), and this has to
be considered when evaluating the impact of designs for transport be considered when evaluating the impact of designs for transport
encryption [RFC5218]. encryption [RFC5218].
6.4. Impact on Operational Cost 6.4. Impact on Operational Cost
Many network operators currently utilise observed transport Some network operators currently use observed transport header
information as a part of their operational practice, and have information as a part of their operational practice, and have
developed tools and operational practices based around currently developed tools and techniques that use information observed in
deployed transports and their applications. Encryption of the currently deployed transports and their applications. A variety of
transport information prevents tools from directly observing this open source and proprietary tools have been deployed that use this
information. A variety of open source and commercial tools have been information for a variety of short and long term measurements.
deployed that utilise this information for a variety of short and Encryption of the transport information prevents tooling from
long term measurements. observing the header information, limiting its utility.
The network will not break just because transport headers are Alternative diagnostic and troubleshooting tools would have to be
encrypted, although alternative diagnostic and troubleshooting tools developed and deployed is transport header encryption is widely
would need to be developed and deployed. Introducing a new protocol deployed. Introducing a new protocol or application might then
or application can require these tool chains and practice to be require these tool chains and practises to be updated, and could in
updated, and could in turn impact operational mechanisms, and turn impact operational mechanisms, and policies. Each change can
policies. Each change can introduce associated costs, including the introduce associated costs, including the cost of collecting data,
cost of collecting data, and the tooling needed to handle multiple and the tooling to handle multiple formats (possibly as these co-
formats (possibly as these co-exist in the network, when measurements exist in the network, when measurements span time periods during
need to span time periods during which changes are deployed, or to which changes are deployed, or to compare with historical data).
compare with historical data). These costs are incurred by an These costs are incurred by an operator to manage the service and
operator to manage the service and debug network issues. debug network issues.
At the time of writing, the additional operational cost of using At the time of writing, the additional operational cost of using
encrypted transports is not yet well understood. Design trade-offs encrypted transports is not yet well understood. Design trade-offs
could mitigate these costs by explicitly choosing to expose selected could mitigate these costs by explicitly choosing to expose selected
information (e.g., header invariants and the spin-bit in QUIC information (e.g., header invariants and the spin-bit in QUIC
[I-D.ietf-quic-transport]), the specification of common log formats, [I-D.ietf-quic-transport]), the specification of common log formats,
and development of alternative approaches. and development of alternative approaches.
6.5. Impact on Research, Development and Deployment 6.5. Impact on Research, Development and Deployment
Evolution and the ability to understand (measure) the impact need to Transport protocol evolution, and the ability to measure and
proceed hand-in-hand. Observable transport headers can provide open understand the impact of protocol changes, have to proceed hand-in-
and verifiable measurement data. Observation of pathologies has a hand. Observable transport headers can provide open and verifiable
critical role in the design of transport protocol mechanisms and measurement data. Observation of pathologies has a critical role in
development of new mechanisms and protocols. This helps the design of transport protocol mechanisms and development of new
understanding the interactions between cooperating protocols and mechanisms and protocols. This helps understanding the interactions
network mechanism, the implications of sharing capacity with other between cooperating protocols and network mechanism, the implications
traffic and the impact of different patterns of usage. The ability of sharing capacity with other traffic and the impact of different
of other stake holders to review transport header traces helps patterns of usage. The ability of other stake holders to review
develop insight into performance and traffic contribution of specific transport header traces helps develop insight into performance and
variants of a protocol. traffic contribution of specific variants of a protocol.
In development of new transport protocol mechanisms, attention needs Development of new transport protocol mechanisms has to consider the
to be paid to the expected scale of deployment. Whatever the scale of deployment and the range of environments in which the
mechanism, experience has shown that it is often difficult to transport is used. Experience has shown that it is often difficult
correctly implement combinations of mechanisms [RFC8085]. Mechanisms to correctly implement new mechanisms [RFC8085], and that mechanisms
often evolve as a protocol matures, or in response to changes in often evolve as a protocol matures, or in response to changes in
network conditions, changes in network traffic, or changes to network conditions, changes in network traffic, or changes to
application usage. Analysis is especially valuable when based on the application usage. Analysis is especially valuable when based on the
behaviour experienced across a range of topologies, vendor equipment, behaviour experienced across a range of topologies, vendor equipment,
and traffic patterns. and traffic patterns.
New transport protocol formats are expected to facilitate an New transport protocol formats are expected to facilitate an
increased pace of transport evolution, and with it the possibility to increased pace of transport evolution, and with it the possibility to
experiment with and deploy a wide range of protocol mechanisms. experiment with and deploy a wide range of protocol mechanisms.
There has been recent interest in a wide range of new transport There has been recent interest in a wide range of new transport
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(PRR), congestion control methods based on measuring bottleneck (PRR), congestion control methods based on measuring bottleneck
bandwidth and round-trip propagation time, the introduction of AQM bandwidth and round-trip propagation time, the introduction of AQM
techniques and new forms of ECN response (e.g., Data Centre TCP, techniques and new forms of ECN response (e.g., Data Centre TCP,
DCTP, and methods proposed for L4S).The growth and diversity of DCTP, and methods proposed for L4S).The growth and diversity of
applications and protocols using the Internet also continues to applications and protocols using the Internet also continues to
expand. For each new method or application it is desirable to build expand. For each new method or application it is desirable to build
a body of data reflecting its behaviour under a wide range of a body of data reflecting its behaviour under a wide range of
deployment scenarios, traffic load, and interactions with other deployment scenarios, traffic load, and interactions with other
deployed/candidate methods. deployed/candidate methods.
Concealing transport header information could reduce the range of Encryption of transport header information could reduce the range of
actors that can observe useful data. This would limit the actors that can observe useful data. This would limit the
information sources available to the Internet community to understand information sources available to the Internet community to understand
the operation of new transport protocols, reducing information to the operation of new transport protocols, reducing information to
inform design decisions and standardisation of the new protocols and inform design decisions and standardisation of the new protocols and
related operational practices. The cooperating dependence of related operational practises. The cooperating dependence of
network, application, and host to provide communication performance network, application, and host to provide communication performance
on the Internet is uncertain when only endpoints (i.e., at user on the Internet is uncertain when only endpoints (i.e., at user
devices and within service platforms) can observe performance, and devices and within service platforms) can observe performance, and
when performance cannot be independently verified by all parties. when performance cannot be independently verified by all parties.
Independently observed data is also important to ensure the health of Independently observed data is also important to ensure the health of
the research and development communities and can help promote the research and development communities and can help promote
acceptance of proposed specifications by the wider community (e.g., acceptance of proposed specifications by the wider community (e.g.,
as a method to judge the safety for Internet deployment) and provides as a method to judge the safety for Internet deployment) and provides
valuable input during standardisation. Open standards motivate a valuable input during standardisation. Open standards motivate a
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7. Conclusions 7. Conclusions
Header encryption and strong integrity checks are being incorporated Header encryption and strong integrity checks are being incorporated
into new transport protocols and have important benefits. The pace into new transport protocols and have important benefits. The pace
of development of transports using the WebRTC data channel, and the of development of transports using the WebRTC data channel, and the
rapid deployment of the QUIC transport protocol, can both be rapid deployment of the QUIC transport protocol, can both be
attributed to using the combination of UDP as a substrate while attributed to using the combination of UDP as a substrate while
providing confidentiality and authentication of the encapsulated providing confidentiality and authentication of the encapsulated
transport headers and payload. transport headers and payload.
To achieve stable Internet operations, the IETF transport community This document has described some current practises, and the
has, to date, relied heavily on measurement and insights of the implications for some stakeholders, when transport layer header
network operations community to understand the trade-offs, and to encryption is used. It does not judge whether these practises are
inform selection of appropriate mechanisms, to ensure a safe, necessary, or endorse the use of any specific practise. Rather, the
reliable, and robust Internet (e.g., [RFC1273],[RFC2914]). intent is to highlight operational tools and practises to consider
when designing transport protocols, so protocol designers can make
The traffic that can be observed by on-path network devices (the informed choice about what transport header fields to encrypt, and
"wire image") is a function of transport protocol design/options, whether it might be beneficial to make an explicit choice to expose
network use, applications, and user characteristics. In general, certain fields to the network. In making such a decision, it is
when only a small proportion of the traffic has a specific important to balance:
(different) characteristic, such traffic seldom leads to operational
concern, although the ability to measure and monitor it is less. The
desire to understand the traffic and protocol interactions typically
grows as the proportion of traffic increases in volume. The
challenges increase when multiple instances of an evolving protocol
contribute to the traffic that share network capacity.
An increased pace of evolution therefore needs to be accompanied by o User Privacy: The less transport header information that is
methods that can be successfully deployed and used across operational exposed to the network, the lower the risk of leaking metadata
networks. This leads to a need for network operators at various that might have privacy implications for the users. Transports
levels (ISPs, enterprises, firewall maintainer, etc.) to identify that chose to expose some header fields need to make a privacy
appropriate operational support functions and procedures. Protocols assessment to understand the privacy cost versus benefit trade-off
that change their transport header format (wire image) or their in making that information available. The process used to define
behaviour (e.g., algorithms that are needed to classify and and expose the QUIC spin bit to the network is an example of such
characterise the protocol), will require new network tooling to be an analysis.
developed to catch-up with each change. If a protocol changes so
that the currently deployed tools and methods are no longer relevant,
then these tools can not be used to measure performance. This can
increase the response-time after faults, and can impact the ability
to manage the network resulting in traffic causing traffic to be
treated inappropriately (e.g., rate-limiting as a result of incorrect
classification or monitoring).
There are benefits in exposing consistent information to the network o Protocol Ossification: Unencrypted transport header fields are
that avoids traffic being inappropriately classified and then likely to ossify rapidly, as middleboxes come to rely on their
receiving a default treatment by the network. The flow label and presence, making it difficult to change the transport in future.
DSCP fields provide examples of how transport information can be made This argues that the choice to expose information to the network
available for network-layer decisions. Extension headers could also is made deliberately and with care, since it is essentially
be used to carry transport information that can inform network-layer defining a stable interface between the transport and the network.
decisions. Other information might also be useful to various Some protocols will want to make that interface as limited as
stakeholders, however this document does not make recommendations possible; other protocols might find value in exposing certain
about what information ought to be exposed, to whom it ought to be information to signal to the network, or in allowing the network
observable, or how this will be achieved. to change certain header fields as signals to the transport. The
visible wire image of a protocol should be explicitly designed.
There are trade-offs and implications of increased use of transport o Impact on Operational Practice: The network operations community
header encryption when designing a protocol. Transport protocol has long relied on being able to understand Internet traffic
designers have often ignored the implications of whether the patterns, both in aggregate and at the flow level, to support
information in transport header fields can or will be used by in- network management, traffic engineering, and troubleshooting.
network devices, and the implications this places on protocol Operational practice has developed based on the information
evolution. This motivates a design that provides confidentiality of available from unencrypted transport headers. The IETF has
header information. This lack of visibility of transport header supported this practice by developing operations and management
information can be expected to impact the ways that protocols are specifications, interface specifications, and associated Best
deployed, standardised, and their operational support. The impact of Current Practises. Widespread deployment of transport protocols
hiding transport headers therefore needs to be considered in the that encrypt their header information might impact network
specification and development of protocols and standards. This has a operations, unless operators can develop alternative practises
potential impact on the way in which the IRTF and IETF develop new that work without access to the transport header information.
protocols, specifications, and guidelines:
o Coexistence of Transport Protocols and Configurations: TCP is o Pace of Evolution: Removing obstacles to change can enable an
currently the predominant transport protocol used over Internet increased pace of evolution. If a protocol changes its transport
paths. Its many variants have broadly consistent approaches to header format (wire image) or their transport behaviour, this can
avoiding congestion collapse, and to ensuring the stability of the result in the currently deployed tools and methods becoming no
Internet. Increased use of transport layer encryption can longer relevant. Where this needs to be accompanied by
overcome ossification, allowing deployment of new transports and development of appropriate operational support functions and
different types of congestion control. This flexibility can be procedures, it can incur a cost in new tooling to catch-up with
beneficial, but it could come at the cost of fragmenting the each change. Protocols that consistently expose observable data
ecosystem. There is little doubt that developers will try to do not require such development, but can suffer from ossification
produce high quality transports for their intended target uses, and need to consider if the exposed protocol metadata has privacy
but it is not yet clear there are sufficient incentives to ensure implications, There is no single deployment context, and therefore
good practice that benefits the wide diversity of requirements for designers need to consider the diversity of operational networks
the Internet community as a whole. (ISPs, enterprises, DDoS mitigation and firewall maintainers,
etc.).
o Supporting Common Specifications: Common open specifications can o Supporting Common Specifications: Common, open, specifications can
stimulate engagement by developers, users, and researchers. stimulate engagement by developers, users, researchers, and the
Increased diversity, and the ability to innovate without public broader community. Increased protocol diversity can be beneficial
scrutiny, risks point solutions that optimise for specific needs, in meeting new requirements, but the ability to innovate without
but accidentally disrupt operations of/in different parts of the public scrutiny risks point solutions that optimise for specific
network. The social contract that maintains the stability of the cases, but that can accidentally disrupt operations of/in
Internet relies on accepting common interworking specifications, different parts of the network. The social contract that
and on it being possible to detect violations. maintains the stability of the Internet relies on accepting common
interworking specifications, and on it being possible to detect
violations. It is important to find new ways of maintaining that
community trust as increased use of transport header encryption
limits visibility into transport behaviour.
o Benchmarking and Understanding Feature Interactions: An o Impact on Benchmarking and Understanding Feature Interactions: An
appropriate vantage point for observation, coupled with timing appropriate vantage point for observation, coupled with timing
information about traffic flows, provides a valuable tool for information about traffic flows, provides a valuable tool for
benchmarking network devices, endpoint stacks, functions, and/or benchmarking network devices, endpoint stacks, functions, and/or
configurations. This can also help with understanding complex configurations. This can also help with understanding complex
feature interactions. An inability to observe transport layer feature interactions. An inability to observe transport layer
header information can make it harder to diagnose and explore header information can make it harder to diagnose and explore
interactions between features at different protocol layers, a interactions between features at different protocol layers, a
side-effect of not allowing a choice of vantage point from which side-effect of not allowing a choice of vantage point from which
this information is observed. New approaches will need to be this information is observed. New approaches might have to be
developed. developed.
o Operational Practice: The network operations community relies on o Impact on Research and Development: Hiding transport information
being able to understand the pattern and requirements of traffic can impede independent research into new mechanisms, measurement
passing over the Internet, both in aggregate and at the flow of behaviour, and development initiatives. Experience shows that
level. These operational practices have developed based on the
information available from unencrypted transport headers. The
IETF supports this activity by developing operations and
management specifications, interface specifications, and
associated Best Current Practice (BCP) specifications. Concealing
transport header information impacts current practice and demand
new specifications.
o Research and Development: Concealing transport information can
impede independent research into new mechanisms, measurement of
behaviour, and development initiatives. Experience shows that
transport protocols are complicated to design and complex to transport protocols are complicated to design and complex to
deploy, and that individual mechanisms need to be evaluated while deploy, and that individual mechanisms have to be evaluated while
considering other mechanisms, across a broad range of network considering other mechanisms, across a broad range of network
topologies and with attention to the impact on traffic sharing the topologies and with attention to the impact on traffic sharing the
capacity. If increased use of transport header encryption results capacity. If increased use of transport header encryption results
in reduced availability of open data, it could eliminate the in reduced availability of open data, it could eliminate the
independent self-checks to the standardisation process that have independent self-checks to the standardisation process that have
previously been in place from research and academic contributors previously been in place from research and academic contributors
(e.g., the role of the IRTF Internet Congestion Control Research (e.g., the role of the IRTF Internet Congestion Control Research
Group (ICCRG) and research publications in reviewing new transport Group (ICCRG) and research publications in reviewing new transport
mechanisms and assessing the impact of their experimental mechanisms and assessing the impact of their deployment).
deployment).
The design of future transport protocols needs to consider encryption Observable transport information information might be useful to
of their transport headers to satisfy security and privacy concerns. various stakeholders. Other stakeholders have incentives to limit
This choice to encrypt all, or part, of the transport layer protocol what can be observed. This document does not make recommendations
headers needs to also take into account the impact on operations, about what information ought to be exposed, to whom it ought to be
standards, and research. As [RFC7258] notes, "Making networks observable, or how this will be achieved. There are also design
unmanageable to mitigate (pervasive monitoring) is not an acceptable choices about where observable fields are placed. For example, one
outcome, but ignoring (pervasive monitoring) would go against the location could be a part of the transport header outside of the
consensus documented here." encryption envelope, another alternative is to carry the information
in a network-layer extension header. New transport protocol designs
ought to explicitly identify any fields that are intended to be
observed, consider if there are alternative ways of providing the
information, and reflect on the implications of observable fields
being used by in-network devices, and how this might impact user
privacy and protocol evolution when these fields become ossified.
As part of a protocol's design, the community therefore needs to As [RFC7258] notes, "Making networks unmanageable to mitigate
weigh the benefits of ossifying common headers versus the potential (pervasive monitoring) is not an acceptable outcome, but ignoring
demerits of exposing specific information that could be observed (pervasive monitoring) would go against the consensus documented
along the network path, to ensure network operators, researchers and here." Providing explicit information can help avoid traffic being
other stakeholders have appropriate tools to manage their networks inappropriately classified, impacting application performance. An
and enable stable operation of the Internet as new protocols are appropriate balance will emerge over time as real instances of this
deployed. An appropriate balance will emerge over time as real tension are analysed [RFC7258]. This balance between information
instances of this tension are analysed [RFC7258]. This balance exposed and information hidden ought to be carefully considered when
between information exposed and information concealed ought to be specifying new transport protocols.
carefully considered when specifying new transport protocols.
8. Security Considerations 8. Security Considerations
This document is about design and deployment considerations for This document is about design and deployment considerations for
transport protocols. Issues relating to security are discussed transport protocols. Issues relating to security are discussed
throughout this document. throughout this document.
Authentication, confidentiality protection, and integrity protection Authentication, confidentiality protection, and integrity protection
are identified as Transport Features by [RFC8095]. As currently are identified as Transport Features by [RFC8095]. As currently
deployed in the Internet, these features are generally provided by a deployed in the Internet, these features are generally provided by a
skipping to change at page 36, line 4 skipping to change at page 36, line 7
throughout this document. throughout this document.
Authentication, confidentiality protection, and integrity protection Authentication, confidentiality protection, and integrity protection
are identified as Transport Features by [RFC8095]. As currently are identified as Transport Features by [RFC8095]. As currently
deployed in the Internet, these features are generally provided by a deployed in the Internet, these features are generally provided by a
protocol or layer on top of the transport protocol protocol or layer on top of the transport protocol
[I-D.ietf-taps-transport-security]. [I-D.ietf-taps-transport-security].
Confidentiality and strong integrity checks have properties that can Confidentiality and strong integrity checks have properties that can
also be incorporated into the design of a transport protocol. also be incorporated into the design of a transport protocol.
Integrity checks can protect an endpoint from undetected modification Integrity checks can protect an endpoint from undetected modification
of protocol fields by network devices, whereas encryption and of protocol fields by network devices, whereas encryption and
obfuscation or greasing can further prevent these headers being obfuscation or greasing can further prevent these headers being
utilised by network devices. Hiding headers can therefore provide utilised by network devices. Preventing observation of headers
the opportunity for greater freedom to update the protocols and can provides an opportunity for greater freedom to update the protocols
ease experimentation with new techniques and their final deployment and can ease experimentation with new techniques and their final
in endpoints. A protocol specification needs to weigh the costs of deployment in endpoints. A protocol specification needs to weigh the
ossifying common headers, versus the potential benefits of exposing costs of ossifying common headers, versus the potential benefits of
specific information that could be observed along the network path to exposing specific information that could be observed along the
provide tools to manage new variants of protocols. network path to provide tools to manage new variants of protocols.
A protocol design that uses header encryption can provide A protocol design that uses header encryption can provide
confidentiality of some or all of the protocol header information. confidentiality of some or all of the protocol header information.
This prevents an on-path device from knowledge of the header field. This prevents an on-path device from knowledge of the header field.
It therefore prevents mechanisms being built that directly rely on It therefore prevents mechanisms being built that directly rely on
the information or seeks to infer semantics of an exposed header the information or seeks to infer semantics of an exposed header
field. Hiding headers reduces visibility into transport metadata, field. Reduces visibility into transport metadata can limit the
and can limit the ability to measure and characterise traffic. It ability to measure and characterise traffic. It can also provide
can also provide privacy benefits in some cases. privacy benefits in some cases.
Extending the transport payload security context to also include the
transport protocol header protects both information with the same
key. A privacy concern would arise if this key was shared with a
third party, e.g., providing access to transport header information
to debug a performance issue, would also result in exposing the
transport payload data to the same third party. A layered security
design that separates network data from payload data would avoid such
risks.
Exposed transport headers are sometimes utilised as a part of the Exposed transport headers are sometimes utilised as a part of the
information to detect anomalies in network traffic. This can be used information to detect anomalies in network traffic. "While PM is an
as the first line of defence to identify potential threats from DOS attack, other forms of monitoring that might fit the definition of PM
or malware and redirect suspect traffic to dedicated nodes can be beneficial and not part of any attack, e.g., network
management functions monitor packets or flows and anti-spam
mechanisms need to see mail message content." [RFC7258]. This can
be used as the first line of defence to identify potential threats
from DOS or malware and redirect suspect traffic to dedicated nodes
responsible for DOS analysis, malware detection, or to perform packet responsible for DOS analysis, malware detection, or to perform packet
"scrubbing" (the normalization of packets so that there are no "scrubbing" (the normalization of packets so that there are no
ambiguities in interpretation by the ultimate destination of the ambiguities in interpretation by the ultimate destination of the
packet). These techniques are currently used by some operators to packet). These techniques are currently used by some operators to
also defend from distributed DOS attacks. also defend from distributed DOS attacks.
Exposed transport header fields are sometimes also utilised as a part Exposed transport header fields are sometimes also utilised as a part
of the information used by the receiver of a transport protocol to of the information used by the receiver of a transport protocol to
protect the transport layer from data injection by an attacker. In protect the transport layer from data injection by an attacker. In
evaluating this use of exposed header information, it is important to evaluating this use of exposed header information, it is important to
skipping to change at page 37, line 16 skipping to change at page 37, line 29
information is accepted by a receiver or obfuscate the accepted information is accepted by a receiver or obfuscate the accepted
header information, e.g., setting a non-predictable initial value for header information, e.g., setting a non-predictable initial value for
a sequence number during a protocol handshake, as in [RFC3550] and a sequence number during a protocol handshake, as in [RFC3550] and
[RFC6056], or a port value that can not be predicted (see section 5.1 [RFC6056], or a port value that can not be predicted (see section 5.1
of [RFC8085]). A receiver could also require additional information of [RFC8085]). A receiver could also require additional information
to be used as a part of a validation check before accepting packets to be used as a part of a validation check before accepting packets
at the transport layer (e.g., utilising a part of the sequence number at the transport layer (e.g., utilising a part of the sequence number
space that is encrypted; or by verifying an encrypted token not space that is encrypted; or by verifying an encrypted token not
visible to an attacker). This would also mitigate against on-path visible to an attacker). This would also mitigate against on-path
attacks. An additional processing cost can be incurred when attacks. An additional processing cost can be incurred when
decryption needs to be attempted before a receiver is able to discard decryption has to be attempted before a receiver is able to discard
injected packets. injected packets.
Open standards motivate a desire for this evaluation to include Open standards motivate a desire for this evaluation to include
independent observation and evaluation of performance data, which in independent observation and evaluation of performance data, which in
turn suggests control over where and when measurement samples are turn suggests control over where and when measurement samples are
collected. This requires consideration of the appropriate balance collected. This requires consideration of the appropriate balance
between encrypting all and no transport information. Open data, and between encrypting all and no transport information. Open data, and
accessibility to tools that can help understand trends in application accessibility to tools that can help understand trends in application
deployment, network traffic and usage patterns can all contribute to deployment, network traffic and usage patterns can all contribute to
understanding security challenges. understanding security challenges.
skipping to change at page 38, line 38 skipping to change at page 39, line 5
Alvestrand, H., "Overview: Real Time Protocols for Alvestrand, H., "Overview: Real Time Protocols for
Browser-based Applications", draft-ietf-rtcweb-overview-19 Browser-based Applications", draft-ietf-rtcweb-overview-19
(work in progress), November 2017. (work in progress), November 2017.
[I-D.ietf-taps-transport-security] [I-D.ietf-taps-transport-security]
Wood, C., Enghardt, T., Pauly, T., Perkins, C., and K. Wood, C., Enghardt, T., Pauly, T., Perkins, C., and K.
Rose, "A Survey of Transport Security Protocols", draft- Rose, "A Survey of Transport Security Protocols", draft-
ietf-taps-transport-security-08 (work in progress), August ietf-taps-transport-security-08 (work in progress), August
2019. 2019.
[I-D.ietf-tls-grease]
Benjamin, D., "Applying GREASE to TLS Extensibility",
draft-ietf-tls-grease-04 (work in progress), August 2019.
[I-D.ietf-tsvwg-rtcweb-qos] [I-D.ietf-tsvwg-rtcweb-qos]
Jones, P., Dhesikan, S., Jennings, C., and D. Druta, "DSCP Jones, P., Dhesikan, S., Jennings, C., and D. Druta, "DSCP
Packet Markings for WebRTC QoS", draft-ietf-tsvwg-rtcweb- Packet Markings for WebRTC QoS", draft-ietf-tsvwg-rtcweb-
qos-18 (work in progress), August 2016. qos-18 (work in progress), August 2016.
[I-D.trammell-plus-abstract-mech] [I-D.trammell-plus-abstract-mech]
Trammell, B., "Abstract Mechanisms for a Cooperative Path Trammell, B., "Abstract Mechanisms for a Cooperative Path
Layer under Endpoint Control", draft-trammell-plus- Layer under Endpoint Control", draft-trammell-plus-
abstract-mech-00 (work in progress), September 2016. abstract-mech-00 (work in progress), September 2016.
skipping to change at page 39, line 17 skipping to change at page 39, line 27
Tutorials. 26;18(3) p2149-2196", November 2014. Tutorials. 26;18(3) p2149-2196", November 2014.
[Measure] Fairhurst, G., Kuehlewind, M., and D. Lopez, "Measurement- [Measure] Fairhurst, G., Kuehlewind, M., and D. Lopez, "Measurement-
based Protocol Design, Eur. Conf. on Networks and based Protocol Design, Eur. Conf. on Networks and
Communications, Oulu, Finland.", June 2017. Communications, Oulu, Finland.", June 2017.
[Quic-Trace] [Quic-Trace]
"https:QUIC trace utilities //github.com/google/quic- "https:QUIC trace utilities //github.com/google/quic-
trace". trace".
[RFC1273] Schwartz, M., "Measurement Study of Changes in Service-
Level Reachability in the Global TCP/IP Internet: Goals,
Experimental Design, Implementation, and Policy
Considerations", RFC 1273, DOI 10.17487/RFC1273, November
1991, <https://www.rfc-editor.org/info/rfc1273>.
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS "Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474, Field) in the IPv4 and IPv6 Headers", RFC 2474,
DOI 10.17487/RFC2474, December 1998, DOI 10.17487/RFC2474, December 1998,
<https://www.rfc-editor.org/info/rfc2474>. <https://www.rfc-editor.org/info/rfc2474>.
[RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z., [RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
and W. Weiss, "An Architecture for Differentiated and W. Weiss, "An Architecture for Differentiated
Services", RFC 2475, DOI 10.17487/RFC2475, December 1998, Services", RFC 2475, DOI 10.17487/RFC2475, December 1998,
<https://www.rfc-editor.org/info/rfc2475>. <https://www.rfc-editor.org/info/rfc2475>.
skipping to change at page 39, line 47 skipping to change at page 40, line 5
[RFC2508] Casner, S. and V. Jacobson, "Compressing IP/UDP/RTP [RFC2508] Casner, S. and V. Jacobson, "Compressing IP/UDP/RTP
Headers for Low-Speed Serial Links", RFC 2508, Headers for Low-Speed Serial Links", RFC 2508,
DOI 10.17487/RFC2508, February 1999, DOI 10.17487/RFC2508, February 1999,
<https://www.rfc-editor.org/info/rfc2508>. <https://www.rfc-editor.org/info/rfc2508>.
[RFC2914] Floyd, S., "Congestion Control Principles", BCP 41, [RFC2914] Floyd, S., "Congestion Control Principles", BCP 41,
RFC 2914, DOI 10.17487/RFC2914, September 2000, RFC 2914, DOI 10.17487/RFC2914, September 2000,
<https://www.rfc-editor.org/info/rfc2914>. <https://www.rfc-editor.org/info/rfc2914>.
[RFC3135] Border, J., Kojo, M., Griner, J., Montenegro, G., and Z.
Shelby, "Performance Enhancing Proxies Intended to
Mitigate Link-Related Degradations", RFC 3135,
DOI 10.17487/RFC3135, June 2001,
<https://www.rfc-editor.org/info/rfc3135>.
[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
of Explicit Congestion Notification (ECN) to IP", of Explicit Congestion Notification (ECN) to IP",
RFC 3168, DOI 10.17487/RFC3168, September 2001, RFC 3168, DOI 10.17487/RFC3168, September 2001,
<https://www.rfc-editor.org/info/rfc3168>. <https://www.rfc-editor.org/info/rfc3168>.
[RFC3234] Carpenter, B. and S. Brim, "Middleboxes: Taxonomy and [RFC3234] Carpenter, B. and S. Brim, "Middleboxes: Taxonomy and
Issues", RFC 3234, DOI 10.17487/RFC3234, February 2002, Issues", RFC 3234, DOI 10.17487/RFC3234, February 2002,
<https://www.rfc-editor.org/info/rfc3234>. <https://www.rfc-editor.org/info/rfc3234>.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
skipping to change at page 42, line 14 skipping to change at page 42, line 14
[RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label
for Equal Cost Multipath Routing and Link Aggregation in for Equal Cost Multipath Routing and Link Aggregation in
Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011, Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011,
<https://www.rfc-editor.org/info/rfc6438>. <https://www.rfc-editor.org/info/rfc6438>.
[RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an [RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May
2014, <https://www.rfc-editor.org/info/rfc7258>. 2014, <https://www.rfc-editor.org/info/rfc7258>.
[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
2015, <https://www.rfc-editor.org/info/rfc7525>.
[RFC7567] Baker, F., Ed. and G. Fairhurst, Ed., "IETF [RFC7567] Baker, F., Ed. and G. Fairhurst, Ed., "IETF
Recommendations Regarding Active Queue Management", Recommendations Regarding Active Queue Management",
BCP 197, RFC 7567, DOI 10.17487/RFC7567, July 2015, BCP 197, RFC 7567, DOI 10.17487/RFC7567, July 2015,
<https://www.rfc-editor.org/info/rfc7567>. <https://www.rfc-editor.org/info/rfc7567>.
[RFC7594] Eardley, P., Morton, A., Bagnulo, M., Burbridge, T., [RFC7594] Eardley, P., Morton, A., Bagnulo, M., Burbridge, T.,
Aitken, P., and A. Akhter, "A Framework for Large-Scale Aitken, P., and A. Akhter, "A Framework for Large-Scale
Measurement of Broadband Performance (LMAP)", RFC 7594, Measurement of Broadband Performance (LMAP)", RFC 7594,
DOI 10.17487/RFC7594, September 2015, DOI 10.17487/RFC7594, September 2015,
<https://www.rfc-editor.org/info/rfc7594>. <https://www.rfc-editor.org/info/rfc7594>.
skipping to change at page 46, line 41 skipping to change at page 46, line 41
repetition. This edit finally gets to this, and eliminates some repetition. This edit finally gets to this, and eliminates some
duplication. This also moves some of the material from section 2 to duplication. This also moves some of the material from section 2 to
reform a clearer conclusion. The scope remains focussed on the usage reform a clearer conclusion. The scope remains focussed on the usage
of transport headers and the implications of encryption - not on of transport headers and the implications of encryption - not on
proposals for new techniques/specifications to be developed. proposals for new techniques/specifications to be developed.
-08 Addressed feedback and completed editorial work, including -08 Addressed feedback and completed editorial work, including
updating the text referring to RFC7872, in preparation for a WGLC. updating the text referring to RFC7872, in preparation for a WGLC.
-09 Updated following WGLC. In particular, thanks to Joe Touch -09 Updated following WGLC. In particular, thanks to Joe Touch
(specific comments and commentry on style and tone); Dimitri Tikonov (specific comments and commentary on style and tone); Dimitri Tikonov
(editorial); Christian Huitema (various) David Black (various). (editorial); Christian Huitema (various); David Black (various).
Ammended privacy considerations based on SECDIR review. Emile Amended privacy considerations based on SECDIR review. Emile Stephan
Stephan (inputs on operations measurement); Various others. (inputs on operations measurement); Various others.
Added summary text and refs to key sections. Note to editors: The Added summary text and refs to key sections. Note to editors: The
section numbers are hard-linked. section numbers are hard-linked.
-10 Updated following additional feedback from 1st WGLC. Comments
from David Black; Tommy Pauly; Ian Swett; Mirja Kuehlewind; Peter
Gutmann; Ekr; and many others via the TSVWG list. Some people
thought that "needed" and "need" could represent requirements in the
document, etc. this has been clarified.
Authors' Addresses Authors' Addresses
Godred Fairhurst Godred Fairhurst
University of Aberdeen University of Aberdeen
Department of Engineering Department of Engineering
Fraser Noble Building Fraser Noble Building
Aberdeen AB24 3UE Aberdeen AB24 3UE
Scotland Scotland
EMail: gorry@erg.abdn.ac.uk EMail: gorry@erg.abdn.ac.uk
 End of changes. 164 change blocks. 
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