draft-ietf-ippm-checksum-trailer-00.txt   draft-ietf-ippm-checksum-trailer-01.txt 
Network Working Group T. Mizrahi Network Working Group T. Mizrahi
Internet Draft Marvell Internet Draft Marvell
Intended status: Informational Intended status: Informational
Expires: June 2015 December 17, 2014 Expires: September 2015 March 9, 2015
UDP Checksum Trailer in OWAMP and TWAMP UDP Checksum Complement in OWAMP and TWAMP
draft-ietf-ippm-checksum-trailer-00.txt draft-ietf-ippm-checksum-trailer-01.txt
Abstract Abstract
The One-Way Active Measurement Protocol (OWAMP) and the Two-Way The One-Way Active Measurement Protocol (OWAMP) and the Two-Way
Active Measurement Protocol (TWAMP) are used for performance Active Measurement Protocol (TWAMP) are used for performance
monitoring in IP networks. Delay measurement is performed in these monitoring in IP networks. Delay measurement is performed in these
protocols by using timestamped test packets. Some implementations use protocols by using timestamped test packets. Some implementations use
hardware-based timestamping engines that integrate the accurate hardware-based timestamping engines that integrate the accurate
transmission timestamp into every outgoing OWAMP/TWAMP test packet transmission timestamp into every outgoing OWAMP/TWAMP test packet
during transmission. Since these packets are transported over UDP, during transmission. Since these packets are transported over UDP,
the UDP checksum field is then updated to reflect this modification. the UDP checksum field is then updated to reflect this modification.
This document proposes to use the last 2 octets of every test packet This document proposes to use the last 2 octets of every test packet
as a Checksum Trailer, allowing timestamping engines to reflect the as a Checksum Complement, allowing timestamping engines to reflect
checksum modification in the last 2 octets rather than in the UDP the checksum modification in the last 2 octets rather than in the UDP
checksum field. The behavior defined in this document is completely checksum field. The behavior defined in this document is completely
interoperable with existing OWAMP/TWAMP implementations. interoperable with existing OWAMP/TWAMP implementations.
Status of this Memo Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
skipping to change at page 1, line 47 skipping to change at page 1, line 47
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt. http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
This Internet-Draft will expire on June 17, 2015. This Internet-Draft will expire on September 9, 2015.
Copyright Notice Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction ................................................. 2 1. Introduction ................................................. 2
2. Conventions used in this document ............................ 4 2. Conventions used in this document ............................ 4
2.1. Terminology ............................................. 4 2.1. Terminology ............................................. 4
2.2. Abbreviations ........................................... 4 2.2. Abbreviations ........................................... 4
3. Using the UDP Checksum Trailer in OWAMP and TWAMP ............ 5 3. Using the UDP Checksum Complement in OWAMP and TWAMP ......... 5
3.1. Overview ................................................ 5 3.1. Overview ................................................ 5
3.2. OWAMP / TWAMP Test Packets with Checksum Trailer ........ 5 3.2. OWAMP / TWAMP Test Packets with Checksum Complement ..... 5
3.2.1. Transmission of OWAMP/TWAMP with Checksum Trailer .. 8 3.2.1. Transmission of OWAMP/TWAMP with Checksum Complement 8
3.2.2. Intermediate Updates of OWAMP/TWAMP with Checksum 3.2.2. Intermediate Updates of OWAMP/TWAMP with Checksum
Trailer ................................................... 9 Complement ................................................ 9
3.2.3. Reception of OWAMP/TWAMP with Checksum Trailer ..... 9 3.2.3. Reception of OWAMP/TWAMP with Checksum Complement .. 9
3.3. Interoperability with Existing Implementations........... 9 3.3. Interoperability with Existing Implementations........... 9
3.4. Using the Checksum Trailer with or without Authentication 9 3.4. Using the Checksum Complement with or without Authentication
............................................................ 9
3.4.1. Checksum Complement in Authenticated Mode........... 9
3.4.2. Checksum Complement in Encrypted Mode .............. 9
4. Security Considerations ..................................... 10 4. Security Considerations ..................................... 10
5. IANA Considerations ......................................... 10 5. IANA Considerations ......................................... 10
6. Acknowledgments ............................................. 10 6. Acknowledgments ............................................. 11
7. References .................................................. 10 7. References .................................................. 11
7.1. Normative References ................................... 10 7.1. Normative References ................................... 11
7.2. Informative References ................................. 11 7.2. Informative References ................................. 11
1. Introduction 1. Introduction
The One-Way Active Measurement Protocol ([OWAMP]) and the Two-Way The One-Way Active Measurement Protocol ([OWAMP]) and the Two-Way
Active Measurement Protocol ([TWAMP]) are used for performance Active Measurement Protocol ([TWAMP]) are used for performance
monitoring in IP networks. monitoring in IP networks.
Delay and delay variation are two of the metrics that OWAMP/TWAMP can Delay and delay variation are two of the metrics that OWAMP/TWAMP can
measure. This measurement is performed using timestamped test measure. This measurement is performed using timestamped test
skipping to change at page 4, line 24 skipping to change at page 4, line 28
are appended to the end of the PTP payload for UDP checksum updates. are appended to the end of the PTP payload for UDP checksum updates.
The value of these two octets can be updated by an intermediate The value of these two octets can be updated by an intermediate
entity, causing the value of the UDP checksum field to remain entity, causing the value of the UDP checksum field to remain
correct. correct.
This document defines a similar concept for [OWAMP] and [TWAMP], This document defines a similar concept for [OWAMP] and [TWAMP],
allowing intermediate entities to update OWAMP/TWAMP test packets and allowing intermediate entities to update OWAMP/TWAMP test packets and
maintain the correctness of the UDP checksum by modifying the last 2 maintain the correctness of the UDP checksum by modifying the last 2
octets of the packet. octets of the packet.
The term Checksum Trailer is used throughout this document and refers The term Checksum Complement is used throughout this document and
to the 2 octets at the end of the UDP payload, used for updating the refers to the 2 octets at the end of the UDP payload, used for
UDP checksum by intermediate entities. updating the UDP checksum by intermediate entities.
The usage of the Checksum Trailer can in some cases simplify the The usage of the Checksum Complement can in some cases simplify the
implementation, since if the packet data is processed in a serial implementation, since if the packet data is processed in a serial
order, it is simpler to first update the timestamp field, and then order, it is simpler to first update the timestamp field, and then
update the Checksum Trailer rather than to update the timestamp and update the Checksum Complement rather than to update the timestamp
then update the UDP checksum, residing at the UDP header. and then update the UDP checksum, residing at the UDP header.
2. Conventions used in this document 2. Conventions used in this document
2.1. Terminology 2.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [KEYWORDS]. document are to be interpreted as described in [KEYWORDS].
2.2. Abbreviations 2.2. Abbreviations
OWAMP One-Way Active Measurement Protocol HMAC Hashed Message Authentication Code
OWAMP One-Way Active Measurement Protocol
PTP Precision Time Protocol PTP Precision Time Protocol
TWAMP Two-Way Active Measurement Protocol TWAMP Two-Way Active Measurement Protocol
UDP User Datagram Protocol UDP User Datagram Protocol
3. Using the UDP Checksum Trailer in OWAMP and TWAMP 3. Using the UDP Checksum Complement in OWAMP and TWAMP
3.1. Overview 3.1. Overview
The UDP Checksum Trailer is a two-octet trailer that is piggybacked The UDP Checksum Complement is a two-octet field that is piggybacked
at the end of the test packet. It resides in the last 2 octets of the at the end of the test packet. It resides in the last 2 octets of the
UDP payload. UDP payload.
+--------------------------------+ +----------------------------------+
| IPv4 / IPv6 Header | | IPv4 / IPv6 Header |
+--------------------------------+ +----------------------------------+
| UDP Header | | UDP Header |
+--------------------------------+ +----------------------------------+
^ | | ^ | |
| | OWAMP / TWAMP | | | OWAMP / TWAMP |
UDP | packet | UDP | packet |
Payload +--------------------------------+ Payload +----------------------------------+
| |UDP Checksum Trailer (2 octets) | | |UDP Checksum Complement (2 octets)|
v +--------------------------------+ v +----------------------------------+
Figure 2 Checksum Trailer in OWAMP/TWAMP Test Packet Figure 2 Checksum Complement in OWAMP/TWAMP Test Packet
3.2. OWAMP / TWAMP Test Packets with Checksum Trailer 3.2. OWAMP / TWAMP Test Packets with Checksum Complement
The One-Way Active Measurement Protocol [OWAMP], and the Two-Way The One-Way Active Measurement Protocol [OWAMP], and the Two-Way
Active Measurement Protocol [TWAMP] both make use of timestamped test Active Measurement Protocol [TWAMP] both make use of timestamped test
packets. The formats of these packets are defined in [OWAMP] and in packets. A Checksum Complement MAY be used in the following cases:
[TWAMP].
o In OWAMP test packets, sent by the sender to the receiver.
o In TWAMP test packets, sent by the sender to the reflector.
o In TWAMP test packets, sent by the reflector to the sender.
OWAMP/TWAMP test packets are transported over UDP, either over IPv4 OWAMP/TWAMP test packets are transported over UDP, either over IPv4
or over IPv6. This document applies to both OWAMP/TWAMP over IPv4 and or over IPv6. This document applies to both OWAMP/TWAMP over IPv4 and
over IPv6. over IPv6.
OWAMP/TWAMP test packets contain a Packet Padding field. This OWAMP/TWAMP test packets contain a Packet Padding field. This
document proposes to use the last 2 octets of the Packet Padding document proposes to use the last 2 octets of the Packet Padding
field as the Checksum Trailer. In this case the Checksum Trailer is field as the Checksum Complement. In this case the Checksum
always the last 2 octets of the UDP payload, and thus the trailer is Complement is always the last 2 octets of the UDP payload, and thus
located UDP Length - 2 octets after the beginning of the UDP header. the field is located UDP Length - 2 octets after the beginning of the
UDP header.
Figure 3 illustrates the OWAMP test packet format including the UDP Figure 3 illustrates the OWAMP test packet format including the UDP
checksum trailer. Checksum Complement.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number | | Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp | | Timestamp |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Estimate | | | Error Estimate | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | | |
. Packet Padding . . Packet Padding .
. . . .
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Checksum Trailer | | | Checksum Complement |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3 Checksum Trailer in OWAMP Test Packets Figure 3 Checksum Complement in OWAMP Test Packets
Figure 4 illustrates the TWAMP test packet format including the UDP Figure 4 illustrates the TWAMP test packet format including the UDP
checksum trailer. Checksum Complement.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number | | Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp | | Timestamp |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Estimate | MBZ | | Error Estimate | MBZ |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Error Estimate | MBZ | | Sender Error Estimate | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender TTL | | | Sender TTL | |
+-+-+-+-+-+-+-+-+ + +-+-+-+-+-+-+-+-+ +
| | | |
. . . .
. Packet Padding . . Packet Padding .
. . . .
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Checksum Trailer | | | Checksum Complement |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4 Checksum Trailer in TWAMP Test Packets Figure 4 Checksum Complement in TWAMP Test Packets
The length of the Packet Padding field in test packets is announced The length of the Packet Padding field in test packets is announced
during the session initiation through the <Padding Length> field in during the session initiation through the <Padding Length> field in
the Request-Session message [OWAMP], or in the Request-TW-Session the Request-Session message [OWAMP], or in the Request-TW-Session
[TWAMP]. [TWAMP].
When a Checksum Trailer is included, the <Padding Length> MUST be When a Checksum Complement is included, the <Padding Length> MUST be
sufficiently long to include the Checksum Trailer: sufficiently long to include the Checksum Complement:
o In OWAMP the padding length is at least 2 octets, allowing the o In OWAMP the padding length is at least 2 octets, allowing the
sender to incorporate the checksum trailer in the last 2 octets of sender to incorporate the Checksum Complement in the last 2 octets
the padding. of the padding.
o In TWAMP the padding length is at least 29 octets. The additional o In TWAMP the padding length is at least 29 octets. The additional
padding is required since the header of reflector test packets is padding is required since the header of reflector test packets is
27 octets longer than the header of sender test packets. Thus, the 27 octets longer than the header of sender test packets. Thus, the
padding in reflector test packets is 27 octets shorter than in padding in reflector test packets is 27 octets shorter than in
sender packet. Using 29 octets of padding in sender test packets sender packet. Using 29 octets of padding in sender test packets
allows both the sender and the reflector to use a 2-octet checksum allows both the sender and the reflector to use a 2-octet Checksum
trailer. Complement.
Note: the 27-octet difference between the sender packet and the Note: the 27-octet difference between the sender packet and the
reflector packet is specifically in unauthenticated mode, whereas reflector packet is specifically in unauthenticated mode, whereas
in authenticated mode the difference between the sender and in authenticated mode the difference between the sender and
receiver packets is 56 octets. As specified in Section 3.4. , the receiver packets is 56 octets. As specified in Section 3.4. , the
checksum trailer should only be used in unauthenticated mode. Checksum Complement should only be used in unauthenticated mode.
o Two optional TWAMP features are defined in [RFC6038]: octet o Two optional TWAMP features are defined in [RFC6038]: octet
reflection and symmetrical size. When at least one of these reflection and symmetrical size. When at least one of these
features is enabled, the Request-TW-Session includes the <Padding features is enabled, the Request-TW-Session includes the <Padding
Length> field, as well as a <Length of padding to reflect> field. Length> field, as well as a <Length of padding to reflect> field.
In this case both fields must be sufficiently long to allow at In this case both fields must be sufficiently long to allow at
least 2 octets of padding in both sender test packets and least 2 octets of padding in both sender test packets and
reflector test packets. reflector test packets.
Specifically, when octet reflection is enabled, the two length Specifically, when octet reflection is enabled, the two length
fields must be defined such that the padding expands at least 2 fields must be defined such that the padding expands at least 2
octets beyond the end of the reflected octets. octets beyond the end of the reflected octets.
As described in Section 1. , the extensions described in this As described in Section 1. , the extensions described in this
document are implemented by two logical layers, a protocol layer and document are implemented by two logical layers, a protocol layer and
a timestamping layer. It is assumed that the two layers are a timestamping layer. It is assumed that the two layers are
synchronized about whether the usage of the Checksum Trailer is synchronized about whether the usage of the Checksum Complement is
enabled or not; since both logical layers reside in the same network enabled or not; since both logical layers reside in the same network
device, it is assumed there is no need for a protocol that device, it is assumed there is no need for a protocol that
synchronizes this information between the two layers. When Checksum synchronizes this information between the two layers. When Checksum
Trailer usage is enabled, the protocol layer must take care to verify Complement usage is enabled, the protocol layer must take care to
that test packets include the necessary padding, and avoiding the verify that test packets include the necessary padding, and avoiding
need for the timestamping layer to verify that en-route test packets the need for the timestamping layer to verify that en-route test
include the necessary padding. packets include the necessary padding.
3.2.1. Transmission of OWAMP/TWAMP with Checksum Trailer 3.2.1. Transmission of OWAMP/TWAMP with Checksum Complement
The transmitter of an OWAMP/TWAMP test packet MAY include a Checksum The transmitter of an OWAMP/TWAMP test packet MAY include a Checksum
Trailer field, incorporated in the last 2 octets of the Packet Complement field, incorporated in the last 2 octets of the Packet
Padding. Padding.
A transmitter that includes a Checksum Trailer in its outgoing test A transmitter that includes a Checksum Complement in its outgoing
packets MUST include a Packet Padding in these packets, the length of test packets MUST include a Packet Padding in these packets, the
which MUST be sufficient to include the checksum trailer. The length length of which MUST be sufficient to include the Checksum
of the padding field is negotiated during session initiation, as Complement. The length of the padding field is negotiated during
described in Section 3.2. session initiation, as described in Section 3.2.
3.2.2. Intermediate Updates of OWAMP/TWAMP with Checksum Trailer 3.2.2. Intermediate Updates of OWAMP/TWAMP with Checksum Complement
An intermediate entity that receives and alters an OWAMP/TWAMP test An intermediate entity that receives and alters an OWAMP/TWAMP test
packet MAY alter the Checksum Trailer field in order to maintain the packet MAY alter the Checksum Complement field in order to maintain
correctness of the UDP checksum value. the correctness of the UDP checksum value.
3.2.3. Reception of OWAMP/TWAMP with Checksum Trailer 3.2.3. Reception of OWAMP/TWAMP with Checksum Complement
This document does not impose new requirements on the receiving end This document does not impose new requirements on the receiving end
of an OWAMP/TWAMP test packet. of an OWAMP/TWAMP test packet.
The UDP layer at the receiving end verifies the UDP Checksum of The UDP layer at the receiving end verifies the UDP Checksum of
received test packets, and the OWAMP/TWAMP layer SHOULD treat the received test packets, and the OWAMP/TWAMP layer SHOULD treat the
Checksum Trailer as part of the Packet Padding. Checksum Complement as part of the Packet Padding.
3.3. Interoperability with Existing Implementations 3.3. Interoperability with Existing Implementations
The behavior defined in this document does not impose new The behavior defined in this document does not impose new
requirements on the reception behavior of an OWAMP receiver or a requirements on the reception behavior of an OWAMP receiver or a
TWAMP reflector, since the existence of the checksum trailer is TWAMP reflector, since the existence of the Checksum Complement is
transparent from the perspective of the receiver/reflector. Thus, the transparent from the perspective of the receiver/reflector. Thus, the
functionality described in this document allows interoperability with functionality described in this document allows interoperability with
existing implementations that comply to [OWAMP] or [TWAMP]. existing implementations that comply to [OWAMP] or [TWAMP].
3.4. Using the Checksum Trailer with or without Authentication 3.4. Using the Checksum Complement with or without Authentication
Both OWAMP and TWAMP may use authentication, as defined in [OWAMP] or Both OWAMP and TWAMP may use authentication or encryption, as defined
[TWAMP]. A Checksum Trailer SHOULD NOT be used when authentication is in [OWAMP] and [TWAMP].
enabled. The Checksum Trailer is effective in unauthenticated mode,
allowing the intermediate entity to perform serial processing of the
packet without storing-and-forwarding it.
On the other hand, when message authentication is used, an 3.4.1. Checksum Complement in Authenticated Mode
intermediate entity that alters test packets must also re-compute the
Message Authentication Code (MAC) accordingly. The MAC update OWAMP and TWAMP test packets can be authenticated using an HMAC
typically requires the intermediate entity to store the packet, re- (Hashed Message Authentication Code). The HMAC covers some of the
compute its MAC, and then forward it. Thus, the benefit of the fields in the test packet header. The HMAC does not cover the
checksum trailer is effectively irrelevant when a MAC is used. Timestamp field and the Packet Padding field.
A Checksum Complement MAY be used when authentication is enabled. In
this case an intermediate entity can timestamp test packets and
update their Checksum Complement field without modifying the HMAC.
3.4.2. Checksum Complement in Encrypted Mode
When OWAMP and TWAMP are used in encrypted mode, the Timestamp field
is encrypted.
A Checksum Complement SHOULD NOT be used in encrypted mode. The
Checksum Complement is effective in unauthenticated and in
authenticated mode, allowing the intermediate entity to perform
serial processing of the packet without storing-and-forwarding it.
On the other hand, in encrypted mode an intermediate entity that
timestamps a test packet must also re-encrypt the packet accordingly.
Re-encryption typically requires the intermediate entity to store the
packet, re-encrypt it, and then forward it. Thus, the benefit of the
Checksum Complement is effectively irrelevant in encrypted mode.
Note: while [OWAMP] and [TWAMP] include an inherent security Note: while [OWAMP] and [TWAMP] include an inherent security
mechanism, these protocols can be secured by other measures, e.g., mechanism, these protocols can be secured by other measures, e.g.,
[IPPMIPsec]. For similar reasons as described above, a Checksum [IPPMIPsec]. For similar reasons as described above, a Checksum
Trailer SHOULD NOT be used in this case. Complement SHOULD NOT be used in this case.
4. Security Considerations 4. Security Considerations
This document describes how a Checksum Trailer extension can be used This document describes how a Checksum Complement extension can be
for maintaining the correctness of the UDP checksum. used for maintaining the correctness of the UDP checksum.
The purpose of this extension is to ease the implementation of The purpose of this extension is to ease the implementation of
accurate timestamping engines, as described in Figure 1. The accurate timestamping engines, as described in Figure 1. The
extension is intended to be used internally in an OWAMP/TWAMP enabled extension is intended to be used internally in an OWAMP/TWAMP enabled
node, and not intended to be used by intermediate switches and node, and not intended to be used by intermediate switches and
routers that reside between the sender and the receiver/reflector. routers that reside between the sender and the receiver/reflector.
Any modification of a test packet by intermediate switches or routers Any modification of a test packet by intermediate switches or routers
should be considered a malicious MITM attack. should be considered a malicious MITM attack.
It is important to emphasize that the scheme described in this It is important to emphasize that the scheme described in this
document does not increase the protocol's vulnerability to MITM document does not increase the protocol's vulnerability to MITM
attacks; a MITM who maliciously modifies a packet and its checksum attacks; a MITM who maliciously modifies a packet and its Checksum
trailer is logically equivalent to a MITM attacker who modifies a Complement is logically equivalent to a MITM attacker who modifies a
packet and its UDP Checksum field. packet and its UDP Checksum field.
The concept described in this document is intended to be used only in The concept described in this document is intended to be used only in
unauthenticated mode. As described in Section 3.4. , the benefits of unauthenticated or in authenticated mode. As described in Section
the Checksum Trailer do not apply when authentication is enabled. 3.4. , the benefits of the Checksum Complement do not apply when
encryption is enabled.
5. IANA Considerations 5. IANA Considerations
There are no IANA actions required by this document. There are no IANA actions required by this document.
RFC Editor: please delete this section before publication. RFC Editor: please delete this section before publication.
6. Acknowledgments 6. Acknowledgments
The authors gratefully acknowledge Al Morton, Greg Mirsky, and Steve
Baillargeon for their helpful comments.
This document was prepared using 2-Word-v2.0.template.dot. This document was prepared using 2-Word-v2.0.template.dot.
7. References 7. References
7.1. Normative References 7.1. Normative References
[KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[IPv6] Deering, S., Hinden, R., "Internet Protocol, Version 6 [IPv6] Deering, S., Hinden, R., "Internet Protocol, Version 6
skipping to change at page 11, line 27 skipping to change at page 11, line 47
Measurement Protocol (TWAMP) Reflect Octets and Measurement Protocol (TWAMP) Reflect Octets and
Symmetrical Size Features", RFC 6038, October 2010. Symmetrical Size Features", RFC 6038, October 2010.
7.2. Informative References 7.2. Informative References
[IEEE1588] IEEE TC 9 Instrumentation and Measurement Society, [IEEE1588] IEEE TC 9 Instrumentation and Measurement Society,
"1588 IEEE Standard for a Precision Clock "1588 IEEE Standard for a Precision Clock
Synchronization Protocol for Networked Measurement and Synchronization Protocol for Networked Measurement and
Control Systems Version 2", IEEE Standard, 2008. Control Systems Version 2", IEEE Standard, 2008.
[IPPMIPsec] Pentikousis, K., Cui, Y., Zhang, E., "Network [IPPMIPsec] Pentikousis, K., Zhang, E., Cui, Y., "IKEv2-based
Performance Measurement for IPsec", draft-ietf-ippm- Shared Secret Key for O/TWAMP", draft-ietf-ippm-ipsec
ipsec (work in progress), September 2014. (work in progress), February 2015.
Authors' Addresses Authors' Addresses
Tal Mizrahi Tal Mizrahi
Marvell Marvell
6 Hamada St. 6 Hamada St.
Yokneam, 20692 Israel Yokneam, 20692 Israel
Email: talmi@marvell.com Email: talmi@marvell.com
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