draft-ietf-tsvwg-datagram-plpmtud-16.txt   draft-ietf-tsvwg-datagram-plpmtud-17.txt 
Internet Engineering Task Force G. Fairhurst Internet Engineering Task Force G. Fairhurst
Internet-Draft T. Jones Internet-Draft T. Jones
Updates: 4821, 4960, 6951, 8085, 8261 (if University of Aberdeen Updates: 4821, 4960, 6951, 8085, 8261 (if University of Aberdeen
approved) M. Tuexen approved) M. Tuexen
Intended status: Standards Track I. Ruengeler Intended status: Standards Track I. Ruengeler
Expires: 10 September 2020 T. Voelker Expires: 24 September 2020 T. Voelker
Muenster University of Applied Sciences Muenster University of Applied Sciences
9 March 2020 23 March 2020
Packetization Layer Path MTU Discovery for Datagram Transports Packetization Layer Path MTU Discovery for Datagram Transports
draft-ietf-tsvwg-datagram-plpmtud-16 draft-ietf-tsvwg-datagram-plpmtud-17
Abstract Abstract
This document describes a robust method for Path MTU Discovery This document describes a robust method for Path MTU Discovery
(PMTUD) for datagram Packetization Layers (PLs). It describes an (PMTUD) for datagram Packetization Layers (PLs). It describes an
extension to RFC 1191 and RFC 8201, which specifies ICMP-based Path extension to RFC 1191 and RFC 8201, which specifies ICMP-based Path
MTU Discovery for IPv4 and IPv6. The method allows a PL, or a MTU Discovery for IPv4 and IPv6. The method allows a PL, or a
datagram application that uses a PL, to discover whether a network datagram application that uses a PL, to discover whether a network
path can support the current size of datagram. This can be used to path can support the current size of datagram. This can be used to
detect and reduce the message size when a sender encounters a packet detect and reduce the message size when a sender encounters a packet
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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."
This Internet-Draft will expire on 10 September 2020. This Internet-Draft will expire on 24 September 2020.
Copyright Notice Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/ Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document. license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights Please review these documents carefully, as they describe your rights
skipping to change at page 2, line 48 skipping to change at page 2, line 48
3. Features Required to Provide Datagram PLPMTUD . . . . . . . . 10 3. Features Required to Provide Datagram PLPMTUD . . . . . . . . 10
4. DPLPMTUD Mechanisms . . . . . . . . . . . . . . . . . . . . . 13 4. DPLPMTUD Mechanisms . . . . . . . . . . . . . . . . . . . . . 13
4.1. PLPMTU Probe Packets . . . . . . . . . . . . . . . . . . 13 4.1. PLPMTU Probe Packets . . . . . . . . . . . . . . . . . . 13
4.2. Confirmation of Probed Packet Size . . . . . . . . . . . 14 4.2. Confirmation of Probed Packet Size . . . . . . . . . . . 14
4.3. Black Hole Detection . . . . . . . . . . . . . . . . . . 15 4.3. Black Hole Detection . . . . . . . . . . . . . . . . . . 15
4.4. The Maximum Packet Size (MPS) . . . . . . . . . . . . . . 16 4.4. The Maximum Packet Size (MPS) . . . . . . . . . . . . . . 16
4.5. Disabling the Effect of PMTUD . . . . . . . . . . . . . . 17 4.5. Disabling the Effect of PMTUD . . . . . . . . . . . . . . 17
4.6. Response to PTB Messages . . . . . . . . . . . . . . . . 17 4.6. Response to PTB Messages . . . . . . . . . . . . . . . . 17
4.6.1. Validation of PTB Messages . . . . . . . . . . . . . 17 4.6.1. Validation of PTB Messages . . . . . . . . . . . . . 17
4.6.2. Use of PTB Messages . . . . . . . . . . . . . . . . . 18 4.6.2. Use of PTB Messages . . . . . . . . . . . . . . . . . 18
5. Datagram Packetization Layer PMTUD . . . . . . . . . . . . . 19 5. Datagram Packetization Layer PMTUD . . . . . . . . . . . . . 20
5.1. DPLPMTUD Components . . . . . . . . . . . . . . . . . . . 20 5.1. DPLPMTUD Components . . . . . . . . . . . . . . . . . . . 20
5.1.1. Timers . . . . . . . . . . . . . . . . . . . . . . . 20 5.1.1. Timers . . . . . . . . . . . . . . . . . . . . . . . 21
5.1.2. Constants . . . . . . . . . . . . . . . . . . . . . . 21 5.1.2. Constants . . . . . . . . . . . . . . . . . . . . . . 21
5.1.3. Variables . . . . . . . . . . . . . . . . . . . . . . 22 5.1.3. Variables . . . . . . . . . . . . . . . . . . . . . . 22
5.1.4. Overview of DPLPMTUD Phases . . . . . . . . . . . . . 23 5.1.4. Overview of DPLPMTUD Phases . . . . . . . . . . . . . 23
5.2. State Machine . . . . . . . . . . . . . . . . . . . . . . 24 5.2. State Machine . . . . . . . . . . . . . . . . . . . . . . 25
5.3. Search to Increase the PLPMTU . . . . . . . . . . . . . . 27 5.3. Search to Increase the PLPMTU . . . . . . . . . . . . . . 28
5.3.1. Probing for a larger PLPMTU . . . . . . . . . . . . . 27 5.3.1. Probing for a larger PLPMTU . . . . . . . . . . . . . 28
5.3.2. Selection of Probe Sizes . . . . . . . . . . . . . . 28 5.3.2. Selection of Probe Sizes . . . . . . . . . . . . . . 29
5.3.3. Resilience to Inconsistent Path Information . . . . . 28 5.3.3. Resilience to Inconsistent Path Information . . . . . 29
5.4. Robustness to Inconsistent Paths . . . . . . . . . . . . 29 5.4. Robustness to Inconsistent Paths . . . . . . . . . . . . 30
6. Specification of Protocol-Specific Methods . . . . . . . . . 29 6. Specification of Protocol-Specific Methods . . . . . . . . . 30
6.1. Application support for DPLPMTUD with UDP or UDP-Lite . . 29 6.1. Application support for DPLPMTUD with UDP or UDP-Lite . . 30
6.1.1. Application Request . . . . . . . . . . . . . . . . . 30 6.1.1. Application Request . . . . . . . . . . . . . . . . . 31
6.1.2. Application Response . . . . . . . . . . . . . . . . 30 6.1.2. Application Response . . . . . . . . . . . . . . . . 31
6.1.3. Sending Application Probe Packets . . . . . . . . . . 30 6.1.3. Sending Application Probe Packets . . . . . . . . . . 31
6.1.4. Initial Connectivity . . . . . . . . . . . . . . . . 30 6.1.4. Initial Connectivity . . . . . . . . . . . . . . . . 31
6.1.5. Validating the Path . . . . . . . . . . . . . . . . . 30 6.1.5. Validating the Path . . . . . . . . . . . . . . . . . 31
6.1.6. Handling of PTB Messages . . . . . . . . . . . . . . 30 6.1.6. Handling of PTB Messages . . . . . . . . . . . . . . 31
6.2. DPLPMTUD for SCTP . . . . . . . . . . . . . . . . . . . . 31 6.2. DPLPMTUD for SCTP . . . . . . . . . . . . . . . . . . . . 32
6.2.1. SCTP/IPv4 and SCTP/IPv6 . . . . . . . . . . . . . . . 31 6.2.1. SCTP/IPv4 and SCTP/IPv6 . . . . . . . . . . . . . . . 32
6.2.1.1. Initial Connectivity . . . . . . . . . . . . . . 31 6.2.1.1. Initial Connectivity . . . . . . . . . . . . . . 32
6.2.1.2. Sending SCTP Probe Packets . . . . . . . . . . . 31 6.2.1.2. Sending SCTP Probe Packets . . . . . . . . . . . 32
6.2.1.3. Validating the Path with SCTP . . . . . . . . . . 32 6.2.1.3. Validating the Path with SCTP . . . . . . . . . . 33
6.2.1.4. PTB Message Handling by SCTP . . . . . . . . . . 32 6.2.1.4. PTB Message Handling by SCTP . . . . . . . . . . 33
6.2.2. DPLPMTUD for SCTP/UDP . . . . . . . . . . . . . . . . 32 6.2.2. DPLPMTUD for SCTP/UDP . . . . . . . . . . . . . . . . 33
6.2.2.1. Initial Connectivity . . . . . . . . . . . . . . 32 6.2.2.1. Initial Connectivity . . . . . . . . . . . . . . 33
6.2.2.2. Sending SCTP/UDP Probe Packets . . . . . . . . . 33 6.2.2.2. Sending SCTP/UDP Probe Packets . . . . . . . . . 34
6.2.2.3. Validating the Path with SCTP/UDP . . . . . . . . 33 6.2.2.3. Validating the Path with SCTP/UDP . . . . . . . . 34
6.2.2.4. Handling of PTB Messages by SCTP/UDP . . . . . . 33 6.2.2.4. Handling of PTB Messages by SCTP/UDP . . . . . . 34
6.2.3. DPLPMTUD for SCTP/DTLS . . . . . . . . . . . . . . . 33 6.2.3. DPLPMTUD for SCTP/DTLS . . . . . . . . . . . . . . . 34
6.2.3.1. Initial Connectivity . . . . . . . . . . . . . . 33 6.2.3.1. Initial Connectivity . . . . . . . . . . . . . . 34
6.2.3.2. Sending SCTP/DTLS Probe Packets . . . . . . . . . 33 6.2.3.2. Sending SCTP/DTLS Probe Packets . . . . . . . . . 34
6.2.3.3. Validating the Path with SCTP/DTLS . . . . . . . 33 6.2.3.3. Validating the Path with SCTP/DTLS . . . . . . . 34
6.2.3.4. Handling of PTB Messages by SCTP/DTLS . . . . . . 34 6.2.3.4. Handling of PTB Messages by SCTP/DTLS . . . . . . 35
6.3. DPLPMTUD for QUIC . . . . . . . . . . . . . . . . . . . . 34 6.3. DPLPMTUD for QUIC . . . . . . . . . . . . . . . . . . . . 35
6.3.1. Initial Connectivity . . . . . . . . . . . . . . . . 34 6.3.1. Initial Connectivity . . . . . . . . . . . . . . . . 35
6.3.2. Sending QUIC Probe Packets . . . . . . . . . . . . . 34 6.3.2. Sending QUIC Probe Packets . . . . . . . . . . . . . 35
6.3.3. Validating the Path with QUIC . . . . . . . . . . . . 35 6.3.3. Validating the Path with QUIC . . . . . . . . . . . . 36
6.3.4. Handling of PTB Messages by QUIC . . . . . . . . . . 35 6.3.4. Handling of PTB Messages by QUIC . . . . . . . . . . 36
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 35 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 36
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 35 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 36
9. Security Considerations . . . . . . . . . . . . . . . . . . . 35 9. Security Considerations . . . . . . . . . . . . . . . . . . . 36
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 37 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 38
10.1. Normative References . . . . . . . . . . . . . . . . . . 37 10.1. Normative References . . . . . . . . . . . . . . . . . . 38
10.2. Informative References . . . . . . . . . . . . . . . . . 38 10.2. Informative References . . . . . . . . . . . . . . . . . 39
Appendix A. Revision Notes . . . . . . . . . . . . . . . . . . . 39 Appendix A. Revision Notes . . . . . . . . . . . . . . . . . . . 40
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 43 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 45
1. Introduction 1. Introduction
The IETF has specified datagram transport using UDP, SCTP, and DCCP, The IETF has specified datagram transport using UDP, SCTP, and DCCP,
as well as protocols layered on top of these transports (e.g., SCTP/ as well as protocols layered on top of these transports (e.g., SCTP/
UDP, DCCP/UDP, QUIC/UDP), and direct datagram transport over the IP UDP, DCCP/UDP, QUIC/UDP), and direct datagram transport over the IP
network layer. This document describes a robust method for Path MTU network layer. This document describes a robust method for Path MTU
Discovery (PMTUD) that can be used with these transport protocols (or Discovery (PMTUD) that can be used with these transport protocols (or
the applications that use their transport service) to discover an the applications that use their transport service) to discover an
appropriate size of packet to use across an Internet path. appropriate size of packet to use across an Internet path.
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receive a packet because of its size. This could be due to receive a packet because of its size. This could be due to
misconfiguration of the layer 2 path between nodes, for instance misconfiguration of the layer 2 path between nodes, for instance
the MTU configured in a layer 2 switch, or misconfiguration of the the MTU configured in a layer 2 switch, or misconfiguration of the
Maximum Receive Unit (MRU). If a packet is dropped by the link, Maximum Receive Unit (MRU). If a packet is dropped by the link,
this will not cause a PTB message to be sent to the original this will not cause a PTB message to be sent to the original
sender. sender.
Another failure could result if a node that is not on the network Another failure could result if a node that is not on the network
path sends a PTB message that attempts to force a sender to change path sends a PTB message that attempts to force a sender to change
the effective PMTU [RFC8201]. A sender can protect itself from the effective PMTU [RFC8201]. A sender can protect itself from
reacting to such messages by utilising the quoted packet within a PTB reacting to such messages by utilizing the quoted packet within a PTB
message payload to validate that the received PTB message was message payload to validate that the received PTB message was
generated in response to a packet that had actually originated from generated in response to a packet that had actually originated from
the sender. However, there are situations where a sender would be the sender. However, there are situations where a sender would be
unable to provide this validation. Examples where validation of the unable to provide this validation. Examples where validation of the
PTB message is not possible include: PTB message is not possible include:
* When a router issuing the ICMP message implements RFC792 * When a router issuing the ICMP message implements RFC792
[RFC0792], it is only required to include the first 64 bits of the [RFC0792], it is only required to include the first 64 bits of the
IP payload of the packet within the quoted payload. There could IP payload of the packet within the quoted payload. There could
be insufficient bytes remaining for the sender to interpret the be insufficient bytes remaining for the sender to interpret the
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validate the message, because validation depends on information validate the message, because validation depends on information
about the active transport flows at an endpoint node (e.g., the about the active transport flows at an endpoint node (e.g., the
socket/address pairs being used, and other protocol header socket/address pairs being used, and other protocol header
information). information).
* When a packet is encapsulated/tunneled over an encrypted * When a packet is encapsulated/tunneled over an encrypted
transport, the tunnel/encapsulation ingress might have transport, the tunnel/encapsulation ingress might have
insufficient context, or computational power, to reconstruct the insufficient context, or computational power, to reconstruct the
transport header that would be needed to perform validation. transport header that would be needed to perform validation.
* A Network Addres Translation (NAT) device that translates a packet * A Network Address Translation (NAT) device that translates a
header, ought to also translate ICMP messages and update the ICMP packet header, ought to also translate ICMP messages and update
quoted packet [RFC5508] in that message. If this is not correctly the ICMP quoted packet [RFC5508] in that message. If this is not
translated then the sender would not be able to associate the correctly translated then the sender would not be able to
message with the PL that originated the packet, and hence this associate the message with the PL that originated the packet, and
ICMP message cannot be validated. hence this ICMP message cannot be validated.
1.2. Packetization Layer Path MTU Discovery 1.2. Packetization Layer Path MTU Discovery
The term Packetization Layer (PL) has been introduced to describe the The term Packetization Layer (PL) has been introduced to describe the
layer that is responsible for placing data blocks into the payload of layer that is responsible for placing data blocks into the payload of
IP packets and selecting an appropriate MPS. This function is often IP packets and selecting an appropriate MPS. This function is often
performed by a transport protocol (e.g., DCCP, RTP, SCTP, QUIC), but performed by a transport protocol (e.g., DCCP, RTP, SCTP, QUIC), but
can also be performed by other encapsulation methods working above can also be performed by other encapsulation methods working above
the transport layer. the transport layer.
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the lower layers, although it can utilize PTB messages when these the lower layers, although it can utilize PTB messages when these
received messages are made available to the PL. received messages are made available to the PL.
The message size guidelines in section 3.2 of the UDP Usage The message size guidelines in section 3.2 of the UDP Usage
Guidelines [RFC8085] state "an application SHOULD either use the Path Guidelines [RFC8085] state "an application SHOULD either use the Path
MTU information provided by the IP layer or implement Path MTU MTU information provided by the IP layer or implement Path MTU
Discovery (PMTUD)", but does not provide a mechanism for discovering Discovery (PMTUD)", but does not provide a mechanism for discovering
the largest size of unfragmented datagram that can be used on a the largest size of unfragmented datagram that can be used on a
network path. The present document updates RFC 8085 to specify this network path. The present document updates RFC 8085 to specify this
method in place of PLPMTUD [RFC4821] and provides a mechanism for method in place of PLPMTUD [RFC4821] and provides a mechanism for
sharing the discovered largest size as the Maximum Packet Size (MPS) sharing the discovered largest size as the MPS (see Section 4.4).
(see Section 4.4).
Section 10.2 of [RFC4821] recommended a PLPMTUD probing method for Section 10.2 of [RFC4821] recommended a PLPMTUD probing method for
the Stream Control Transport Protocol (SCTP). SCTP utilizes probe the Stream Control Transport Protocol (SCTP). SCTP utilizes probe
packets consisting of a minimal sized HEARTBEAT chunk bundled with a packets consisting of a minimal sized HEARTBEAT chunk bundled with a
PAD chunk as defined in [RFC4820]. However, RFC 4821 did not provide PAD chunk as defined in [RFC4820]. However, RFC 4821 did not provide
a complete specification. The present document replaces this by a complete specification. The present document replaces this by
providing a complete specification. providing a complete specification.
The Datagram Congestion Control Protocol (DCCP) [RFC4340] requires The Datagram Congestion Control Protocol (DCCP) [RFC4340] requires
implementations to support Classical PMTUD and states that a DCCP implementations to support Classical PMTUD and states that a DCCP
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[RFC8261]. [RFC8261].
2. Terminology 2. 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", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
Other terminology is directly copied from [RFC4821], and the The following terminology is defined. Relevant terms are directly
definitions in [RFC1122]. copied from [RFC4821], and the definitions in [RFC1122].
Acknowledged PL: A PL that includes a mechanism that can confirm
successful delivery of datagrams to the remote PL endpoint (e.g.,
SCTP). Typically, the PL receiver returns acknowledgments
corresponding to the received datagrams, which can be utilised to
detect black-holing of packets (c.f., Unacknowledged PL).
Actual PMTU: The Actual PMTU is the PMTU of a network path between a Actual PMTU: The Actual PMTU is the PMTU of a network path between a
sender PL and a destination PL, which the DPLPMTUD algorithm seeks sender PL and a destination PL, which the DPLPMTUD algorithm seeks
to determine. to determine.
Black Hole: A Black Hole is encountered when a sender is unaware Black Hole: A Black Hole is encountered when a sender is unaware
that packets are not being delivered to the destination end point. that packets are not being delivered to the destination end point.
Two types of Black Hole are relevant to DPLPMTUD: Two types of Black Hole are relevant to DPLPMTUD:
* Packets encounter a packet Black Hole when packets are not * Packets encounter a packet Black Hole when packets are not
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Classical Path MTU Discovery: Classical PMTUD is a process described Classical Path MTU Discovery: Classical PMTUD is a process described
in [RFC1191] and [RFC8201], in which nodes rely on PTB messages to in [RFC1191] and [RFC8201], in which nodes rely on PTB messages to
learn the largest size of unfragmented packet that can be used learn the largest size of unfragmented packet that can be used
across a network path. across a network path.
Datagram: A datagram is a transport-layer protocol data unit, Datagram: A datagram is a transport-layer protocol data unit,
transmitted in the payload of an IP packet. transmitted in the payload of an IP packet.
Effective PMTU: The Effective PMTU is the current estimated value Effective PMTU: The Effective PMTU is the current estimated value
for PMTU that is used by a PMTUD. This is equivalent to the for PMTU that is used by a PMTUD. This is equivalent to the
PLPMTU derived by PLPMTUD. PLPMTU derived by PLPMTUD plus the size of any headers added below
the PL, including the IP layer headers.
EMTU_S: The Effective MTU for sending (EMTU_S) is defined in EMTU_S: The Effective MTU for sending (EMTU_S) is defined in
[RFC1122] as "the maximum IP datagram size that may be sent, for a [RFC1122] as "the maximum IP datagram size that may be sent, for a
particular combination of IP source and destination addresses...". particular combination of IP source and destination addresses...".
EMTU_R: The Effective MTU for receiving (EMTU_R) is designated in EMTU_R: The Effective MTU for receiving (EMTU_R) is designated in
[RFC1122] as the largest datagram size that can be reassembled by [RFC1122] as the largest datagram size that can be reassembled by
EMTU_R (Effective MTU to receive). EMTU_R (Effective MTU to receive).
Link: A Link is a communication facility or medium over which nodes Link: A Link is a communication facility or medium over which nodes
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could more properly be called the IP MTU, to be consistent with could more properly be called the IP MTU, to be consistent with
how other standards organizations use the acronym. This includes how other standards organizations use the acronym. This includes
the IP header, but excludes link layer headers and other framing the IP header, but excludes link layer headers and other framing
that is not part of IP or the IP payload. Other standards that is not part of IP or the IP payload. Other standards
organizations generally define the link MTU to include the link organizations generally define the link MTU to include the link
layer headers. This specification continues the requirement in layer headers. This specification continues the requirement in
[RFC4821], that states "All links MUST enforce their MTU: links [RFC4821], that states "All links MUST enforce their MTU: links
that might non- deterministically deliver packets that are larger that might non- deterministically deliver packets that are larger
than their rated MTU MUST consistently discard such packets." than their rated MTU MUST consistently discard such packets."
MAX_PMTU: The MAX_PMTU is the largest size of PLPMTU that DPLPMTUD MAX_PLPMTU: The MAX_PLPMTU is the largest size of PLPMTU that
will attempt to use. DPLPMTUD will attempt to use.
MPS: The Maximum Packet Size (MPS) is the largest size of MIN_PLPMTU: The MIN_PLPMTU is the smallest size of PLPMTU that
application data block that can be sent across a network path by a DPLPMTUD will attempt to use.
PL. In DPLPMTUD this quantity is derived from the PLPMTU by
taking into consideration the size of the lower protocol layer
headers. Probe packets generated by DPLPMTUD can have a size
larger than the MPS.
MIN_PMTU: The MIN_PMTU is the smallest size of PLPMTU that DPLPMTUD MPS: MPS: The Maximum Packet Size (MPS) is the largest size of
will attempt to use. application data block that can be sent across a network path by a
PL using a single Datagram.
Packet: A Packet is the IP header plus the IP payload. Packet: A Packet is the IP header plus the IP payload.
Packetization Layer (PL): The Packetization Layer (PL) is a layer of Packetization Layer (PL): The PL is a layer of the network stack
the network stack that places data into packets and performs that places data into packets and performs transport protocol
transport protocol functions. Examples of a PL include: TCP, functions. Examples of a PL include: TCP, SCTP, SCTP over DTLS or
SCTP, SCTP over DTLS or QUIC. QUIC.
Path: The Path is the set of links and routers traversed by a packet Path: The Path is the set of links and routers traversed by a packet
between a source node and a destination node by a particular flow. between a source node and a destination node by a particular flow.
Path MTU (PMTU): The Path MTU (PMTU) is the minimum of the Link MTU Path MTU (PMTU): The Path MTU (PMTU) is the minimum of the Link MTU
of all the links forming a network path between a source node and of all the links forming a network path between a source node and
a destination node. a destination node, as used by PMTUD.
PTB_SIZE: The PTB_SIZE is a value reported in a validated PTB PTB_SIZE: The PTB_SIZE is a value reported in a validated PTB
message that indicates next hop link MTU of a router along the message that indicates next hop link MTU of a router along the
path. path.
PLPMTU: The Packetization Layer PMTU is an estimate of the actual PL_PTB_SIZE: The size reported in a validated PTB message, reduced
PMTU provided by the DPLPMTUD algorithm. by the size of all headers added by layers below the PL.
PLPMTU: The Packetization Layer PMTU is an estimate of the largest
size of PL datagram that can be sent by a path, controled by
PLPMTUD.
PLPMTUD: Packetization Layer Path MTU Discovery (PLPMTUD), the PLPMTUD: Packetization Layer Path MTU Discovery (PLPMTUD), the
method described in this document for datagram PLs, which is an method described in this document for datagram PLs, which is an
extension to Classical PMTU Discovery. extension to Classical PMTU Discovery.
Probe packet: A probe packet is a datagram sent with a purposely Probe packet: A probe packet is a datagram sent with a purposely
chosen size (typically the current PLPMTU or larger) to detect if chosen size (typically the current PLPMTU or larger) to detect if
packets of this size can be successfully sent end-to-end across packets of this size can be successfully sent end-to-end across
the network path. the network path.
Unacknowledged PL: A PL that does not itself provide a mechanism to
confirm delivery of datagrams to the remote PL endpoint (e.g.,
UDP), and therefore requires DPLPMTUD to provide a mechanism to
detect black-holing of packets (c.f., Acknowledged PL).
3. Features Required to Provide Datagram PLPMTUD 3. Features Required to Provide Datagram PLPMTUD
The principles expressed in [RFC4821] apply to the use of the The principles expressed in [RFC4821] apply to the use of the
technique with any PL. TCP PLPMTUD has been defined using standard technique with any PL. TCP PLPMTUD has been defined using standard
TCP protocol mechanisms. Unlike TCP, datagram PLs require additional TCP protocol mechanisms. Unlike TCP, a datagram PL requires
mechanisms and considerations to implement PLPMTUD. additional mechanisms and considerations to implement PLPMTUD.
The requirements for datagram PLPMTUD are: The requirements for datagram PLPMTUD are:
1. PLPMTU: The PLPMTU (specified as the effective PMTU in Section 1 1. Managing the PLPMTU: For datagram PLs, the PLPMTU is managed by
of [RFC1191]) is equivalent to the EMTU_S (specified in DPLPMTUD. A PL MUST NOT send a datagram (other than a probe
[RFC1122]). For datagram PLs,] the PLPMTU is managed by packet) with a size at the PL layer that is larger than the
DPLPMTUD. A PL MUST NOT send a packet (other than a probe current PLPMTU.
packet) with a size larger than the current PLPMTU at the
network layer.
2. Probe packets: On request, a DPLPMTUD sender is REQUIRED to be 2. Probe packets: On request, a DPLPMTUD sender is REQUIRED to be
able to transmit a packet larger than the PLMPMTU. This is used able to transmit a packet larger than the PLMPMTU. This is used
to send a probe packet. In IPv4, a probe packet MUST be sent to send a probe packet. In IPv4, a probe packet MUST be sent
with the Don't Fragment (DF) bit set in the IP header, and with the Don't Fragment (DF) bit set in the IP header, and
without network layer endpoint fragmentation. In IPv6, a probe without network layer endpoint fragmentation. In IPv6, a probe
packet is always sent without source fragmentation (as specified packet is always sent without source fragmentation (as specified
in section 5.4 of [RFC8201]). in section 5.4 of [RFC8201]).
3. Reception feedback: The destination PL endpoint is REQUIRED to 3. Reception feedback: The destination PL endpoint is REQUIRED to
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4. Probe loss recovery: It is RECOMMENDED to use probe packets that 4. Probe loss recovery: It is RECOMMENDED to use probe packets that
do not carry any user data that would require retransmission if do not carry any user data that would require retransmission if
lost. Most datagram transports permit this. If a probe packet lost. Most datagram transports permit this. If a probe packet
contains user data requiring retransmission in case of loss, the contains user data requiring retransmission in case of loss, the
PL (or layers above) are REQUIRED to arrange any retransmission/ PL (or layers above) are REQUIRED to arrange any retransmission/
repair of any resulting loss. The PL is REQUIRED to be robust repair of any resulting loss. The PL is REQUIRED to be robust
in the case where probe packets are lost due to other reasons in the case where probe packets are lost due to other reasons
(including link transmission error, congestion). (including link transmission error, congestion).
5. PMTU parameters: A DPLPMTUD sender is RECOMMENDED to utilise 5. PMTU parameters: A DPLPMTUD sender is RECOMMENDED to utilize
information about the maximum size of packet that can be information about the maximum size of packet that can be
transmitted by the sender on the local link (e.g., the local transmitted by the sender on the local link (e.g., the local
Link MTU). It MAY utilize similar information about the Link MTU). It MAY utilize similar information about the maximum
receiver when this is supplied (note this could be less than size a receiver can accept when this is supplied (note this
EMTU_R). This avoids implementations trying to send probe could be less than EMTU_R). This avoids implementations trying
packets that can not be transmitted by the local link. Too high to send probe packets that can not be transferred by the local
of a value could reduce the efficiency of the search algorithm. link. Too high of a value could reduce the efficiency of the
Some applications also have a maximum transport protocol data search algorithm. Some applications also have a maximum
unit (PDU) size, in which case there is no benefit from probing transport protocol data unit (PDU) size, in which case there is
for a size larger than this (unless a transport allows no benefit from probing for a size larger than this (unless a
multiplexing multiple applications PDUs into the same datagram). transport allows multiplexing multiple applications PDUs into
the same datagram).
6. Processing PTB messages: A DPLPMTUD sender MAY optionally 6. Processing PTB messages: A DPLPMTUD sender MAY optionally
utilize PTB messages received from the network layer to help utilize PTB messages received from the network layer to help
identify when a network path does not support the current size identify when a network path does not support the current size
of probe packet. Any received PTB message MUST be validated of probe packet. Any received PTB message MUST be validated
before it is used to update the PLPMTU discovery information before it is used to update the PLPMTU discovery information
[RFC8201]. This validation confirms that the PTB message was [RFC8201]. This validation confirms that the PTB message was
sent in response to a packet originating by the sender, and sent in response to a packet originating by the sender, and
needs to be performed before the PLPMTU discovery method reacts needs to be performed before the PLPMTU discovery method reacts
to the PTB message. A PTB message MUST NOT be used to increase to the PTB message. A PTB message MUST NOT be used to increase
the PLPMTU [RFC8201], but could trigger a probe to test for a the PLPMTU [RFC8201], but could trigger a probe to test for a
larger PLPMTU. A PTB_SIZE greater than the currently probed larger PLPMTU. A PL_PTB_SIZE that is greater than that
MUST be ignored. currently probed MUST be ignored. A valid PTB_SIZE is converted
to a PL_PTB_SIZE before it is to be used in the DPLPMTUD state
machine.
7. Probing and congestion control: The decision about when to send 7. Probing and congestion control: The decision about when to send
a probe packet does not need to be limited by the congestion a probe packet does not need to be limited by the congestion
controller. When not controlled by the congestion controller, controller. When not controlled by the congestion controller,
the interval between probe packets MUST be at least one RTT. If the interval between probe packets MUST be at least one RTT. If
transmission of probe packets is limited by the congestion transmission of probe packets is limited by the congestion
controller, this could result in transmission of probe packets controller, this could result in transmission of probe packets
being delayed. being delayed or suspended during congestion.
8. Loss of a probe packet SHOULD NOT be treated as an indication of 8. Loss of a probe packet SHOULD NOT be treated as an indication of
congestion and SHOULD NOT trigger a congestion control reaction congestion and SHOULD NOT trigger a congestion control reaction
[RFC4821], because this could result in unnecessary reduction of [RFC4821], because this could result in unnecessary reduction of
the sending rate. the sending rate.
9. An update to the PLPMTU (or MPS) MUST NOT modify the congestion 9. An update to the PLPMTU (or MPS) MUST NOT modify the congestion
window measured in bytes [RFC4821]. Therefore, an increase in window measured in bytes [RFC4821]. Therefore, an increase in
the packet size does not cause an increase the data rate in the packet size does not cause an increase the data rate in
bytes per second. bytes per second.
10. Probing and flow control: Flow control at the PL concerns the 10. Probing and flow control: Flow control at the PL concerns the
end-to-end flow of data using the PL service. This does not end-to-end flow of data using the PL service. This does not
apply to DPLPMTU when probe packets use a design that does not apply to DPLPMTU when probe packets use a design that does not
carry user data to the remote application. carry user data to the remote application.
11. Shared PLPMTU state: The PLPMTU value MAY also be stored with 11. Shared PLPMTU state: The PMTU value calculated from the PLPMTU
the corresponding entry associated with the destination in the MAY also be stored with the corresponding entry associated with
IP layer cache, and used by other PL instances. The the destination in the IP layer cache, and used by other PL
specification of PLPMTUD [RFC4821] states: "If PLPMTUD updates instances. The specification of PLPMTUD [RFC4821] states: "If
the MTU for a particular path, all Packetization Layer sessions PLPMTUD updates the MTU for a particular path, all Packetization
that share the path representation (as described in Section 5.2 Layer sessions that share the path representation (as described
of [RFC4821]) SHOULD be notified to make use of the new MTU". in Section 5.2 of [RFC4821]) SHOULD be notified to make use of
Such methods MUST be robust to the wide variety of underlying the new MTU". Such methods MUST be robust to the wide variety
network forwarding behaviors. Section 5.2 of [RFC8201] provides of underlying network forwarding behaviors. Section 5.2 of
guidance on the caching of PMTU information and also the [RFC8201] provides guidance on the caching of PMTU information
relation to IPv6 flow labels. and also the relation to IPv6 flow labels.
In addition, the following principles are stated for design of a In addition, the following principles are stated for design of a
DPLPMTUD method: DPLPMTUD method:
* Maximum Packet Size (MPS): A PL MAY be designed to segment data * A PL MAY be designed to segment data blocks larger than the MPS
blocks larger than the MPS into multiple datagrams. However, not into multiple datagrams. However, not all datagram PLs support
all datagram PLs support segmentation of data blocks. It is segmentation of data blocks. It is RECOMMENDED that methods avoid
RECOMMENDED that methods avoid forcing an application to use an forcing an application to use an arbitrary small MPS for
arbitrary small MPS for transmission while the method is searching transmission while the method is searching for the currently
for the currently supported PLPMTU. A reduced MPS can adversely supported PLPMTU. A reduced MPS can adversely impact the
impact the performance of an application. performance of an application.
* To assist applications in choosing a suitable data block size, the * To assist applications in choosing a suitable data block size, the
PL is RECOMMENDED to provide a primitive that returns the MPS PL is RECOMMENDED to provide a primitive that returns the MPS
derived from the PLPMTU to the higher layer using the PL. The derived from the PLPMTU to the higher layer using the PL. The
value of the MPS can change following a change in the path, or value of the MPS can change following a change in the path, or
loss of probe packets. loss of probe packets.
* Path validation: It is RECOMMENDED that methods are robust to path * Path validation: It is RECOMMENDED that methods are robust to path
changes that could have occurred since the path characteristics changes that could have occurred since the path characteristics
were last confirmed, and to the possibility of inconsistent path were last confirmed, and to the possibility of inconsistent path
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block in a datagram without the padding data). This retransmited block in a datagram without the padding data). This retransmited
data block might possibly need to be sent using a smaller PLPMTU, data block might possibly need to be sent using a smaller PLPMTU,
which could need the PL to to use a smaller packet size to traverse which could need the PL to to use a smaller packet size to traverse
the end-to-end path. (This could utilize endpoint network-layer or a the end-to-end path. (This could utilize endpoint network-layer or a
PL that can re-segment the data block into multiple datagrams). PL that can re-segment the data block into multiple datagrams).
DPLPMTUD MAY choose to use only one of these methods to simplify the DPLPMTUD MAY choose to use only one of these methods to simplify the
implementation. implementation.
Probe messages sent by a PL MUST contain enough information to Probe messages sent by a PL MUST contain enough information to
uniquely identify the probe within Maximum Segment Lifetime, while uniquely identify the probe within Maximum Segment Lifetime (e.g.,
being robust to reordering and replay of probe response and PTB including a unique identifier from the PL or the DPLPMTUD
messages. implementation), while being robust to reordering and replay of probe
response and PTB messages.
4.2. Confirmation of Probed Packet Size 4.2. Confirmation of Probed Packet Size
The PL needs a method to determine (confirm) when probe packets have The PL needs a method to determine (confirm) when probe packets have
been successfully received end-to-end across a network path. been successfully received end-to-end across a network path.
Transport protocols can include end-to-end methods that detect and Transport protocols can include end-to-end methods that detect and
report reception of specific datagrams that they send (e.g., DCCP and report reception of specific datagrams that they send (e.g., DCCP and
SCTP provide keep-alive/heartbeat features). When supported, this SCTP provide keep-alive/heartbeat features). When supported, this
mechanism MAY also be used by DPLPMTUD to acknowledge reception of a mechanism MAY also be used by DPLPMTUD to acknowledge reception of a
skipping to change at page 15, line 15 skipping to change at page 15, line 26
Section 6 specifies this function for a set of IETF-specified Section 6 specifies this function for a set of IETF-specified
protocols. protocols.
4.3. Black Hole Detection 4.3. Black Hole Detection
Black Hole Detection is triggered by an indication that the network Black Hole Detection is triggered by an indication that the network
path could be unable to support the current PLPMTU size. path could be unable to support the current PLPMTU size.
There are three ways to detect black holes: There are three ways to detect black holes:
* A validated PTB message can be received that indicates a PTB_SIZE * A validated PTB message can be received that indicates a
less than the current PLPMTU. A DPLPMTUD method MUST NOT rely PL_PTB_SIZE less than the current PLPMTU. A DPLPMTUD method MUST
soley on this method. NOT rely solely on this method.
* A PL can use the DPLPMTUD probing mechanism to periodically * A PL can use the DPLPMTUD probing mechanism to periodically
generate probe packets of the size of the current PLPMTU (e.g., generate probe packets of the size of the current PLPMTU (e.g.,
using the confirmation timer Section 5.1.1). A timer tracks using the confirmation timer Section 5.1.1). A timer tracks
whether acknowledgments are received. Successive loss of probes whether acknowledgments are received. Successive loss of probes
is an indication that the current path no longer supports the is an indication that the current path no longer supports the
PLPMTU (e.g., when the number of probe packets sent without PLPMTU (e.g., when the number of probe packets sent without
receiving an acknowledgement, PROBE_COUNT, becomes greater than receiving an acknowledgment, PROBE_COUNT, becomes greater than
MAX_PROBES). MAX_PROBES).
* A PL can utilise an event that indicates the network path no * A PL can utilize an event that indicates the network path no
longer sustains the sender's PLPMTU size. This could use a longer sustains the sender's PLPMTU size. This could use a
mechanism implemented within the PL to detect excessive loss of mechanism implemented within the PL to detect excessive loss of
data sent with a specific packet size and then conclude that this data sent with a specific packet size and then conclude that this
excessive loss could be a result of an invalid PLPMTU (as in excessive loss could be a result of an invalid PLPMTU (as in
PLPMTUD for TCP [RFC4821]). PLPMTUD for TCP [RFC4821]).
A PL MAY inhibit sending probe packets when no application data has A PL MAY inhibit sending probe packets when no application data has
been sent since the previous probe packet. A PL preferring to use an been sent since the previous probe packet. A PL preferring to use an
up-to-data PLPMTU once user data is sent again, MAY choose to up-to-data PLPMTU once user data is sent again, MAY choose to
continue PLPMTU discovery for each path. However, this could result continue PLPMTU discovery for each path. However, this could result
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the new PLPMTU can be successfully used across the path. A probe the new PLPMTU can be successfully used across the path. A probe
packet could need to have a size less than the size of the data block packet could need to have a size less than the size of the data block
generated by the application. generated by the application.
4.4. The Maximum Packet Size (MPS) 4.4. The Maximum Packet Size (MPS)
The result of probing determines a usable PLPMTU, which is used to The result of probing determines a usable PLPMTU, which is used to
set the MPS used by the application. The MPS is smaller than the set the MPS used by the application. The MPS is smaller than the
PLPMTU because it is reduced by the size of PL headers (including the PLPMTU because it is reduced by the size of PL headers (including the
overhead of security-related fields such as an AEAD tag and TLS overhead of security-related fields such as an AEAD tag and TLS
record layer padding) and any IP options or extensions added to the record layer padding). The relationship between the MPS and the
PL packet. The relationship between the MPS and the PLPMTUD is PLPMTUD is illustrated in Figure 1.
illustrated in Figure 1.
any additional any additional
headers .--- MPS -----. headers .--- MPS -----.
| | | | | |
v v v v v v
+------------------------------+ +------------------------------+
| IP | ** | PL | protocol data | | IP | ** | PL | protocol data |
+------------------------------+ +------------------------------+
<---------- PLPMTU ------------> <----- PLPMTU ----->
<---------- PMTU -------------->
Figure 1: Relationship between MPS and PLPMTU Figure 1: Relationship between MPS and PLPMTU
A PL is unable to send a packet (other than a probe packet) with a A PL is unable to send a packet (other than a probe packet) with a
size larger than the current PLPMTU at the network layer. To avoid size larger than the current PLPMTU at the network layer. To avoid
this, a PL MAY be designed to segment data blocks larger than the MPS this, a PL MAY be designed to segment data blocks larger than the MPS
into multiple datagrams. into multiple datagrams.
DPLPMTUD seeks to avoid IP fragmentation. An attempt to send a data DPLPMTUD seeks to avoid IP fragmentation. An attempt to send a data
block larger than the MPS will therefore fail if a PL is unable to block larger than the MPS will therefore fail if a PL is unable to
segment data. To determine the largest data block that can be sent, segment data. To determine the largest data block that can be sent,
a PL SHOULD provide applications with a primitive that returns the a PL SHOULD provide applications with a primitive that returns the
Maximum Packet Size (MPS), derived from the current PLPMTU. MPS, derived from the current PLPMTU.
If DPLPMTUD results in a change to the MPS, the application needs to If DPLPMTUD results in a change to the MPS, the application needs to
adapt to the new MPS. A particular case can arise when packets have adapt to the new MPS. A particular case can arise when packets have
been sent with a size less than the MPS and the PLPMTU was been sent with a size less than the MPS and the PLPMTU was
subsequently reduced. If these packets are lost, the PL MAY segment subsequently reduced. If these packets are lost, the PL MAY segment
the data using the new MPS. If a PL is unable to re-segment a the data using the new MPS. If a PL is unable to re-segment a
previously sent datagram (e.g., [RFC4960]), then the sender either previously sent datagram (e.g., [RFC4960]), then the sender either
discards the datagram or could perform retransmission using network- discards the datagram or could perform retransmission using network-
layer fragmentation to form multiple IP packets not larger than the layer fragmentation to form multiple IP packets not larger than the
PLPMTU. For IPv4, the use of endpoint fragmentation by the sender is PLPMTU. For IPv4, the use of endpoint fragmentation by the sender is
preferred over clearing the DF-bit in the IPv4 header. Operational preferred over clearing the DF-bit in the IPv4 header. Operational
experience reveals that IP fragmentation can reduce the reliability experience reveals that IP fragmentation can reduce the reliability
of Internet communication [I-D.ietf-intarea-frag-fragile], which may of Internet communication [I-D.ietf-intarea-frag-fragile], which may
reduce the success of retransmission. reduce the success of retransmission.
4.5. Disabling the Effect of PMTUD 4.5. Disabling the Effect of PMTUD
A PL implementing this specification MUST suspend network layer A PL implementing this specification MUST suspend network layer
processing of outgoing packets that enforces a PMTU processing of outgoing packets that enforces a PMTU
[RFC1191][RFC8201] for each flow utilising DPLPMTUD, and instead use [RFC1191][RFC8201] for each flow utilizing DPLPMTUD, and instead use
DPLPMTUD to control the size of packets that are sent by a flow. DPLPMTUD to control the size of packets that are sent by a flow.
This removes the need for the network layer to drop or fragment sent This removes the need for the network layer to drop or fragment sent
packets that have a size greater than the PMTU. packets that have a size greater than the PMTU.
4.6. Response to PTB Messages 4.6. Response to PTB Messages
This method requires the DPLPMTUD sender to validate any received PTB This method requires the DPLPMTUD sender to validate any received PTB
message before using the PTB information. The response to a PTB message before using the PTB information. The response to a PTB
message depends on the PTB_SIZE indicated in the PTB message, the message depends on the PL_PTB_SIZE calculated from the PTB_SIZE in
state of the PLPMTUD state machine, and the IP protocol being used. the PTB message, the state of the PLPMTUD state machine, and the IP
protocol being used.
Section 4.6.1 first describes validation for both IPv4 ICMP Section 4.6.1 first describes validation for both IPv4 ICMP
Unreachable messages (type 3) and ICMPv6 Packet Too Big messages, Unreachable messages (type 3) and ICMPv6 Packet Too Big messages,
both of which are referred to as PTB messages in this document. both of which are referred to as PTB messages in this document.
4.6.1. Validation of PTB Messages 4.6.1. Validation of PTB Messages
This section specifies utilization of PTB messages. This section specifies utilization of PTB messages.
* A simple implementation MAY ignore received PTB messages and in * A simple implementation MAY ignore received PTB messages and in
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PL endpoints. A datagram application that uses well-known source and PL endpoints. A datagram application that uses well-known source and
destination ports ought to also rely on other information to complete destination ports ought to also rely on other information to complete
this validation. this validation.
These checks are intended to provide protection from packets that These checks are intended to provide protection from packets that
originate from a node that is not on the network path. A PTB message originate from a node that is not on the network path. A PTB message
that does not complete the validation MUST NOT be further utilized by that does not complete the validation MUST NOT be further utilized by
the DPLPMTUD method. the DPLPMTUD method.
PTB messages that have been validated MAY be utilized by the DPLPMTUD PTB messages that have been validated MAY be utilized by the DPLPMTUD
algorithm, but MUST NOT be used directly to set the PLPMTU. A method algorithm, but MUST NOT be used directly to set the PLPMTU. The
that utilizes these PTB messages can improve the speed at the which PL_PTB_SIZE is smaller than the PTB_SIZE because it is reduced by
the algorithm detects an appropriate PLPMTU by triggering an headers below the PL including any IP options or extensions added to
immediate probe for the PTB_SIZE, compared to one that relies solely the PL packet. A method that utilizes these PTB messages can improve
on probing using a timer-based search algorithm. Section 4.6.2 the speed at which the algorithm detects an appropriate PLPMTU by
describes this processing. triggering an immediate probe for the PL_PTB_SIZE (resulting in a
network-layer packet of size PTB_SIZE), compared to one that relies
solely on probing using a timer-based search algorithm.
Section 4.6.2 describes this processing.
4.6.2. Use of PTB Messages 4.6.2. Use of PTB Messages
A set of checks are intended to provide protection from a router that Before using the size reported in the PTB message it must first be
reports an unexpected PTB_SIZE. The PL also needs to check that the converted to a PL_PTB_SIZE. A set of checks are intended to provide
indicated PTB_SIZE is less than the size used by probe packets and at protection from a router that reports an unexpected PTB_SIZE. The PL
least the minimum size accepted. also needs to check that the indicated PL_PTB_SIZE is less than the
size used by probe packets and at least the minimum size accepted.
This section provides a summary of how PTB messages can be utilized. This section provides a summary of how PTB messages can be utilized.
This processing depends on the PTB_SIZE and the current value of a This processing depends on the PL_PTB_SIZE and the current value of a
set of variables: set of variables:
PTB_SIZE < MIN_PMTU PL_PTB_SIZE < MIN_PLPMTU
* Invalid PTB_SIZE see Section 4.6.1. * Invalid PL_PTB_SIZE see Section 4.6.1.
* PTB message ought to be discarded without further processing * PTB message ought to be discarded without further processing
(e. g. PLPMTU not modified). (i.e., PLPMTU is not modified).
* The information could be utilized as an input to trigger * The information could be utilized as an input to a trigger that
enabling a resilience mode. would enable a resilience mode.
MIN_PMTU < PTB_SIZE < BASE_PMTU MIN_PLPMTU < PL_PTB_SIZE < BASE_PLPMTU
* A robust PL MAY enter an error state (see Section 5.2) for an * A robust PL MAY enter an error state (see Section 5.2) for an
IPv4 path when the PTB_SIZE reported in the PTB message is IPv4 path when the PL_PTB_SIZE reported in the PTB message is
larger than or equal to 68 bytes [RFC0791] and when this is larger than or equal to 68 bytes [RFC0791] and when this is
less than the BASE_PMTU. less than the BASE_PLPMTU.
* A robust PL MAY enter an error state (see Section 5.2) for an * A robust PL MAY enter an error state (see Section 5.2) for an
IPv6 path when the PTB_SIZE reported in the PTB message is IPv6 path when the PL_PTB_SIZE reported in the PTB message is
larger than or equal to 1280 bytes [RFC8200] and when this is larger than or equal to 1280 bytes [RFC8200] and when this is
less than the BASE_PMTU. less than the BASE_PLPMTU.
PTB_SIZE = PLPMTU PL_PTB_SIZE = PLPMTU
* Completes the search for a larger PLPMTU. * Completes the search for a larger PLPMTU.
PTB_SIZE > PROBED_SIZE PL_PTB_SIZE > PROBED_SIZE
* Inconsistent network signal. * Inconsistent network signal.
* PTB message ought to be discarded without further processing * PTB message ought to be discarded without further processing
(e. g. PLPMTU not modified). (i.e., PLPMTU is not modified).
* The information could be utilized as an input to trigger * The information could be utilized as an input to trigger
enabling a resilience mode. enabling a resilience mode.
BASE_PMTU <= PTB_SIZE < PLPMTU BASE_PLPMTU <= PL_PTB_SIZE < PLPMTU
* This could be an indication of a black hole. The PLPMTU SHOULD * This could be an indication of a black hole. The PLPMTU SHOULD
be set to BASE_PMTU (the PLPMTU is reduced to the BASE_PMTU to be set to BASE_PLPMTU (the PLPMTU is reduced to the BASE_PLPMTU
avoid unnecessary packet loss when a black hole is to avoid unnecessary packet loss when a black hole is
encountered). encountered).
* The PL ought to start a search to quickly discover the new * The PL ought to start a search to quickly discover the new
PLPMTU. The PTB_SIZE reported in the PTB message can be used PLPMTU. The PL_PTB_SIZE reported in the PTB message can be
to initialize a search algorithm. used to initialize a search algorithm.
PLPMTU < PTB_SIZE < PROBED_SIZE PLPMTU < PL_PTB_SIZE < PROBED_SIZE
* The PLPMTU continues to be valid, but the last PROBED_SIZE * The PLPMTU continues to be valid, but the size of a packet used
searched was larger than the actual PMTU. to search (PROBED_SIZE) was larger than the actual PMTU.
* The PLPMTU is not updated. * The PLPMTU is not updated.
* The PL can use the reported PTB_SIZE from the PTB message as * The PL can use the reported PL_PTB_SIZE from the PTB message as
the next search point when it resumes the search algorithm. the next search point when it resumes the search algorithm.
5. Datagram Packetization Layer PMTUD 5. Datagram Packetization Layer PMTUD
This section specifies Datagram PLPMTUD (DPLPMTUD). The method can This section specifies Datagram PLPMTUD (DPLPMTUD). The method can
be introduced at various points (as indicated with * in the figure be introduced at various points (as indicated with * in the figure
below) in the IP protocol stack to discover the PLPMTU so that an below) in the IP protocol stack to discover the PLPMTU so that an
application can utilize an appropriate MPS for the current network application can utilize an appropriate MPS for the current network
path. path.
DPLPMTUD SHOULD NOT be used by an upper PL or application if it is DPLPMTUD SHOULD NOT be used by an upper PL or application if it is
already used in a lower layer, DPLPMTUD SHOULD only be performed once already used in a lower layer, DPLPMTUD SHOULD only be performed once
between a pair of endpoints. A PL MUST adjust the MPS indicated by between a pair of endpoints. A PL MUST adjust the MPS indicated by
DPLPMTUD to account for any additional overhead introduced by the PL. DPLPMTUD to account for any additional overhead introduced by the PL.
+----------------------+ +----------------------+
| Application* | | Application* |
+-+-------+----+----+--+ +-----+------------+---+
| | | | | |
+---+--+ +--+--+ | +-+---+ +---+--+ +--+--+
| QUIC*| |UDPO*| | |SCTP*| | QUIC*| |SCTP*|
+---+--+ +--+--+ | +--+--+ +---+--+ +-+-+-+
| | | | | | | |
+-------+--+ | | | +---+ +----+ |
| | | | | | |
+-+-+--+ | +-+--+-+ |
| UDP | | | UDP | |
+---+--+ | +---+--+ |
| | | |
+--------------+-----+-+ +-----------+-------+--+
| Network Interface | | Network Interface |
+----------------------+ +----------------------+
Figure 2: Examples where DPLPMTUD can be implemented Figure 2: Examples where DPLPMTUD can be implemented
The central idea of DPLPMTUD is probing by a sender. Probe packets The central idea of DPLPMTUD is probing by a sender. Probe packets
are sent to find the maximum size of user message that can be are sent to find the maximum size of user message that can be
completely transferred across the network path from the sender to the completely transferred across the network path from the sender to the
destination. destination.
The following sections identify the components needed for The following sections identify the components needed for
implementation, provides an overview of the phases of operation, and implementation, provides an overview of the phases of operation, and
skipping to change at page 21, line 38 skipping to change at page 22, line 4
An implementation could implement the various timers using a single An implementation could implement the various timers using a single
timer. timer.
5.1.2. Constants 5.1.2. Constants
The following constants are defined: The following constants are defined:
MAX_PROBES: The MAX_PROBES is the maximum value of the PROBE_COUNT MAX_PROBES: The MAX_PROBES is the maximum value of the PROBE_COUNT
counter (see Section 5.1.3). MAX_PROBES represents the limit for counter (see Section 5.1.3). MAX_PROBES represents the limit for
the number of consecutive probe attempts of any size. Search the number of consecutive probe attempts of any size. Search
algorithms benefit from a MAX_PROBES value greater than 1 because algorithms benefit from a MAX_PROBES valugreater than 1 because
this can provide robustness to isolated packet loss. The default this can provide robustness to isolated packet loss. The default
value of MAX_PROBES is 3. value of MAX_PROBES is 3.
MIN_PMTU: The MIN_PMTU is the smallest allowed probe packet size. MIN_PLPMTU: The MIN_PLPMTU is the smallest allowed probe packet
For IPv6, this value is 1280 bytes, as specified in [RFC8200]. size. For IPv6, this value is 1280 bytes, as specified in
For IPv4, the minimum value is 68 bytes. [RFC8200]. For IPv4, the minimum value is 68 bytes.
Note: An IPv4 router is required to be able to forward a datagram Note: An IPv4 router is required to be able to forward a datagram
of 68 bytes without further fragmentation. This is the combined of 68 bytes without further fragmentation. This is the combined
size of an IPv4 header and the minimum fragment size of 8 bytes. size of an IPv4 header and the minimum fragment size of 8 bytes.
In addition, receivers are required to be able to reassemble In addition, receivers are required to be able to reassemble
fragmented datagrams at least up to 576 bytes, as stated in fragmented datagrams at least up to 576 bytes, as stated in
section 3.3.3 of [RFC1122]. section 3.3.3 of [RFC1122].
MAX_PMTU: The MAX_PMTU is the largest size of PLPMTU. This has to MAX_PLPMTU: The MAX_PLPMTU is the largest size of PLPMTU. This has
be less than or equal to the minimum of the local MTU of the to be less than or equal to the maximum size of the PL packet that
outgoing interface and the destination PMTU for receiving. An can be sent on the outgoing interface (constrained by the local
application, or PL, MAY choose a smaller MAX_PMTU when there is no interface MTU). When known, this also ought to be less than the
need to send packets larger than a specific size. maximum size of PL packet that can be received by the remote
endpoint (constrained by EMTU_R). It can be limited by the design
or configuration of the PL being used. An application, or PL, MAY
choose a smaller MAX_PLPMTU when there is no need to send packets
larger than a specific size.
BASE_PMTU: The BASE_PMTU is a configured size expected to work for BASE_PLPMTU: The BASE_PLPMTU is a configured size expected to work
most paths. The size is equal to or larger than the MIN_PMTU and for most paths. The size is equal to or larger than the
smaller than the MAX_PMTU. In the case of IPv6, this value is MIN_PLPMTU and smaller than the MAX_PLPMTU. In the case of IPv6,
1280 bytes [RFC8200]. When using IPv4, a size of 1200 bytes is this value is 1280 bytes [RFC8200]. When using IPv4, a size of
RECOMMENDED. 1200 bytes is RECOMMENDED.
5.1.3. Variables 5.1.3. Variables
This method utilizes a set of variables: This method utilizes a set of variables:
PROBED_SIZE: The PROBED_SIZE is the size of the current probe PROBED_SIZE: The PROBED_SIZE is the size of the current probe
packet. This is a tentative value for the PLPMTU, which is packet. This is a tentative value for the PLPMTU, which is
awaiting confirmation by an acknowledgment. awaiting confirmation by an acknowledgment.
PROBE_COUNT: The PROBE_COUNT is a count of the number of successive PROBE_COUNT: The PROBE_COUNT is a count of the number of successive
skipping to change at page 22, line 34 skipping to change at page 23, line 4
PROBE_COUNT: The PROBE_COUNT is a count of the number of successive PROBE_COUNT: The PROBE_COUNT is a count of the number of successive
unsuccessful probe packets that have been sent. Each time a probe unsuccessful probe packets that have been sent. Each time a probe
packet is acknowledged, the value is set to zero. (Some probe packet is acknowledged, the value is set to zero. (Some probe
loss is expected while searching, therefore loss of a single probe loss is expected while searching, therefore loss of a single probe
is not an indication of a PMTU problem.) is not an indication of a PMTU problem.)
The figure below illustrates the relationship between the packet size The figure below illustrates the relationship between the packet size
constants and variables at a point of time when the DPLPMTUD constants and variables at a point of time when the DPLPMTUD
algorithm performs path probing to increase the size of the PLPMTU. algorithm performs path probing to increase the size of the PLPMTU.
A probe packet has been sent of size PROBED_SIZE. Once this is A probe packet has been sent of size PROBED_SIZE. Once this is
acknowledged, the PLPMTU will raise to PROBED_SIZE allowing the acknowledged, the PLPMTU will raise to PROBED_SIZE allowing the
DPLPMTUD algorithm to further increase PROBED_SIZE towards the actual DPLPMTUD algorithm to further increase PROBED_SIZE toward sending a
PMTU. probe with the size of the actual PMTU.
MIN_PMTU MAX_PMTU MIN_PLPMTU MAX_PLPMTU
<--------------------------------------------------> <------------------------------------------->
| | | | | | |
v | | v v | |
BASE_PMTU | v Actual PMTU BASE_PLPMTU | v
| PROBED_SIZE | PROBED_SIZE
v v
PLPMTU PLPMTU
Figure 3: Relationships between packet size constants and variables Figure 3: Relationships between packet size constants and variables
5.1.4. Overview of DPLPMTUD Phases 5.1.4. Overview of DPLPMTUD Phases
This section provides a high-level informative view of the DPLPMTUD This section provides a high-level informative view of the DPLPMTUD
method, by describing the movement of the method through several method, by describing the movement of the method through several
phases of operation. More detail is available in the state machine phases of operation. More detail is available in the state machine
Section 5.2. Section 5.2.
+------+ +------+
+------->| Base |----------------+ Connectivity +------->| Base |-----------------+ Connectivity
| +------+ | or BASE_PMTU | +------+ | or BASE_PLPMTU
| | | confirmation failed | | | confirmation failed
| | v | | v
| | Connectivity +-------+ | | Connectivity +-------+
| | and BASE_PMTU | Error | | | and BASE_PLPMTU | Error |
| | confirmed +-------+ | | confirmed +-------+
| | | Consistent | | | Consistent
| v | connectivity | v | connectivity
PLPMTU | +--------+ | and BASE_PMTU PLPMTU | +--------+ | and BASE_PLPMTU
confirmation | | Search |<--------------+ confirmed confirmation | | Search |<---------------+ confirmed
failed | +--------+ failed | +--------+
| ^ | | ^ |
| | | | | |
| Raise | | Search | Raise | | Search
| timer | | algorithm | timer | | algorithm
| expired | | completed | expired | | completed
| | | | | |
| | v | | v
| +-----------------+ | +-----------------+
+---| Search Complete | +---| Search Complete |
+-----------------+ +-----------------+
Figure 4: DPLPMTUD Phases Figure 4: DPLPMTUD Phases
Base: The Base Phase confirms connectivity to the remote peer using Base: The Base Phase confirms connectivity to the remote peer using
packets of the BASE_PMTU. This phase is implicit for a packets of the BASE_PLPMTU. This phase is implicit for a
connection-oriented PL (where it can be performed in a PL connection-oriented PL (where it can be performed in a PL
connection handshake). A connectionless PL sends an acknowledged connection handshake). A connectionless PL sends a probe packet
probe packet to confirm that the remote peer is reachable. The and uses acknowledgment of this probe packet to confirm that the
sender also confirms that BASE_PMTU is supported across the remote peer is reachable.
network path.
The sender also confirms that BASE_PLPMTU is supported across the
network path. This may be achieved using a PL mechanism (e.g.,
using a handshake packet of size BASE_PLPMTU), or by sending a
probe packet of size BASE_PLPMTU and confirming that this is
received.
A probe packet of size BASE_PLPMTU can be sent immediately on the
initial entry to the Base Phase (following a connectivity check).
A PL that does not wish to support a path with a PLPMTU less than A PL that does not wish to support a path with a PLPMTU less than
BASE_PMTU can simplify the phase into a single step by performing BASE_PLPMTU can simplify the phase into a single step by
the connectivity checks with a probe of the BASE_PMTU size. performing the connectivity checks with a probe of the BASE_PLPMTU
size.
Once confirmed, DPLPMTUD enters the Search Phase. If this phase Once confirmed, DPLPMTUD enters the Search Phase. If this phase
fails to confirm, DPLPMTUD enters the Error Phase. fails to confirm, DPLPMTUD enters the Error Phase.
Search: The Search Phase utilizes a search algorithm to send probe Search: The Search Phase utilizes a search algorithm to send probe
packets to seek to increase the PLPMTU. The algorithm concludes packets to seek to increase the PLPMTU. The algorithm concludes
when it has found a suitable PLPMTU, by entering the Search when it has found a suitable PLPMTU, by entering the Search
Complete Phase. Complete Phase.
A PL could respond to PTB messages using the PTB to advance or A PL could respond to PTB messages using the PTB to advance or
skipping to change at page 24, line 25 skipping to change at page 24, line 48
CONFIRMATION_TIMER to periodically repeat a probe packet for the CONFIRMATION_TIMER to periodically repeat a probe packet for the
current PLPMTU size. If the sender is unable to confirm current PLPMTU size. If the sender is unable to confirm
reachability (e.g., if the CONFIRMATION_TIMER expires) or the PL reachability (e.g., if the CONFIRMATION_TIMER expires) or the PL
signals a lack of reachability, DPLPMTUD enters the Base phase. signals a lack of reachability, DPLPMTUD enters the Base phase.
The PMTU_RAISE_TIMER is used to periodically resume the search The PMTU_RAISE_TIMER is used to periodically resume the search
phase to discover if the PLPMTU can be raised. Black Hole phase to discover if the PLPMTU can be raised. Black Hole
Detection causes the sender to enter the Base Phase. Detection causes the sender to enter the Base Phase.
Error: The Error Phase is entered when there is conflicting or Error: The Error Phase is entered when there is conflicting or
invalid PLPMTU information for the path (e.g. a failure to support invalid PLPMTU information for the path (e.g., a failure to
the BASE_PMTU) that cause DPLPMTUD to be unable to progress and support the BASE_PLPMTU) that cause DPLPMTUD to be unable to
the PLPMTU is lowered. progress and the PLPMTU is lowered.
DPLPMTUD remains in the Error Phase until a consistent view of the DPLPMTUD remains in the Error Phase until a consistent view of the
path can be discovered and it has also been confirmed that the path can be discovered and it has also been confirmed that the
path supports the BASE_PMTU (or DPLPMTUD is suspended). path supports the BASE_PLPMTU (or DPLPMTUD is suspended).
An implementation that only reduces the PLPMTU to a suitable size An implementation that only reduces the PLPMTU to a suitable size
would be sufficient to ensure reliable operation, but can be very would be sufficient to ensure reliable operation, but can be very
inefficient when the actual PMTU changes or when the method (for inefficient when the actual PMTU changes or when the method (for
whatever reason) makes a suboptimal choice for the PLPMTU. whatever reason) makes a suboptimal choice for the PLPMTU.
A full implementation of DPLPMTUD provides an algorithm enabling the A full implementation of DPLPMTUD provides an algorithm enabling the
DPLPMTUD sender to increase the PLPMTU following a change in the DPLPMTUD sender to increase the PLPMTU following a change in the
characteristics of the path, such as when a link is reconfigured with characteristics of the path, such as when a link is reconfigured with
a larger MTU, or when there is a change in the set of links traversed a larger MTU, or when there is a change in the set of links traversed
skipping to change at page 25, line 13 skipping to change at page 26, line 13
Note: Not all changes are shown to simplify the diagram. Note: Not all changes are shown to simplify the diagram.
| | | |
| Start | PL indicates loss | Start | PL indicates loss
| | of connectivity | | of connectivity
v v v v
+---------------+ +---------------+ +---------------+ +---------------+
| DISABLED | | ERROR | | DISABLED | | ERROR |
+---------------+ PROBE_TIMER expiry: +---------------+ +---------------+ PROBE_TIMER expiry: +---------------+
| PL indicates PROBE_COUNT = MAX_PROBES or ^ | | PL indicates PROBE_COUNT = MAX_PROBES or ^ |
| connectivity PTB: PTB_SIZE < BASE_PMTU | | | connectivity PTB: PLPTB_SIZE < BASE_PLPMTU | |
+--------------------+ +---------------+ | +--------------------+ +---------------+ |
| | | | | |
v | BASE_PMTU Probe | v | BASE_PLPMTU Probe |
+---------------+ acked | +---------------+ acked |
| BASE |----------------------+ | BASE |----------------------+
+---------------+ | +---------------+ |
^ | ^ ^ | ^ | ^ ^ |
Black hole detected | | | | Black hole detected | Black hole detected | | | | Black hole detected |
+--------------------+ | | +--------------------+ | +--------------------+ | | +--------------------+ |
| +----+ | | | +----+ | |
| PROBE_TIMER expiry: | | | PROBE_TIMER expiry: | |
| PROBE_COUNT < MAX_PROBES | | | PROBE_COUNT < MAX_PROBES | |
| | | | | |
| PMTU_RAISE_TIMER expiry | | | PMTU_RAISE_TIMER expiry | |
| +-----------------------------------------+ | | | +-----------------------------------------+ | |
| | | | | | | | | |
| | v | v | | v | v
+---------------+ +---------------+ +---------------+ +---------------+
|SEARCH_COMPLETE| | SEARCHING | |SEARCH_COMPLETE| | SEARCHING |
+---------------+ +---------------+ +---------------+ +---------------+
| ^ ^ | | ^ | ^ ^ | | ^
| | | | | | | | | | | |
| | +-----------------------------------------+ | | | | +-----------------------------------------+ | |
| | MAX_PMTU Probe acked or | | | | MAX_PLPMTU Probe acked or | |
| | PROBE_TIMER expiry: PROBE_COUNT = MAX_PROBES or | | | | PROBE_TIMER expiry: PROBE_COUNT = MAX_PROBES or | |
+----+ PTB: PTB_SIZE = PLPMTU +----+ +----+ PTB: PLPTB_SIZE = PLPMTU +----+
CONFIRMATION_TIMER expiry: PROBE_TIMER expiry: CONFIRMATION_TIMER expiry: PROBE_TIMER expiry:
PROBE_COUNT < MAX_PROBES or PROBE_COUNT < MAX_PROBES or PROBE_COUNT < MAX_PROBES or PROBE_COUNT < MAX_PROBES or
PLPMTU Probe acked Probe acked or PTB: PLPMTU Probe acked Probe acked or PTB:
PLPMTU < PTB_SIZE < PROBED_SIZE PLPMTU < PLPTB_SIZE < PROBED_SIZE
Figure 5: State machine for Datagram PLPMTUD Figure 5: State machine for Datagram PLPMTUD
The following states are defined: The following states are defined:
DISABLED: The DISABLED state is the initial state before probing has DISABLED: The DISABLED state is the initial state before probing has
started. It is also entered from any other state, when the PL started. It is also entered from any other state, when the PL
indicates loss of connectivity. This state is left, once the PL indicates loss of connectivity. This state is left once the PL
indicates connectivity to the remote PL. indicates connectivity to the remote PL. When transitioning to
the BASE state, a probe packet of size BASE_PLPMTU can be sent
immediately.
BASE: The BASE state is used to confirm that the BASE_PMTU size is BASE: The BASE state is used to confirm that the BASE_PLPMTU size is
supported by the network path and is designed to allow an supported by the network path and is designed to allow an
application to continue working when there are transient application to continue working when there are transient
reductions in the actual PMTU. It also seeks to avoid long reductions in the actual PMTU. It also seeks to avoid long
periods when a sender searching for a larger PLPMTU is unaware periods when a sender searching for a larger PLPMTU is unaware
that packets are not being delivered due to a packet or ICMP Black that packets are not being delivered due to a packet or ICMP Black
Hole. Hole.
On entry, the PROBED_SIZE is set to the BASE_PMTU size and the On entry, the PROBED_SIZE is set to the BASE_PLPMTU size and the
PROBE_COUNT is set to zero. PROBE_COUNT is set to zero.
Each time a probe packet is sent, the PROBE_TIMER is started. The Each time a probe packet is sent, the PROBE_TIMER is started. The
state is exited when the probe packet is acknowledged, and the PL state is exited when the probe packet is acknowledged, and the PL
sender enters the SEARCHING state. sender enters the SEARCHING state.
The state is also left when the PROBE_COUNT reaches MAX_PROBES or The state is also left when the PROBE_COUNT reaches MAX_PROBES or
a received PTB message is validated. This causes the PL sender to a received PTB message is validated. This causes the PL sender to
enter the ERROR state. enter the ERROR state.
SEARCHING: The SEARCHING state is the main probing state. This SEARCHING: The SEARCHING state is the main probing state. This
state is entered when probing for the BASE_PMTU was successful. state is entered when probing for the BASE_PLPMTU was successful.
Each time a probe packet is acknowledged, the PROBE_COUNT is set Each time a probe packet is acknowledged, the PROBE_COUNT is set
to zero, the PLPMTU is set to the PROBED_SIZE and then the to zero, the PLPMTU is set to the PROBED_SIZE and then the
PROBED_SIZE is increased using the search algorithm. PROBED_SIZE is increased using the search algorithm.
When a probe packet is sent and not acknowledged within the period When a probe packet is sent and not acknowledged within the period
of the PROBE_TIMER, the PROBE_COUNT is incremented and a new probe of the PROBE_TIMER, the PROBE_COUNT is incremented and a new probe
packet is transmitted. packet is transmitted.
The state is exited to enter SEARCH_COMPLETE when the PROBE_COUNT The state is exited to enter SEARCH_COMPLETE when the PROBE_COUNT
reaches MAX_PROBES, a validated PTB is received that corresponds reaches MAX_PROBES, a validated PTB is received that corresponds
to the last successfully probed size (PTB_SIZE = PLPMTU), or a to the last successfully probed size (PL_PTB_SIZE = PLPMTU), or a
probe of size MAX_PMTU is acknowledged (PLPMTU = MAX_PMTU). probe of size MAX_PLPMTU is acknowledged (PLPMTU = MAX_PLPMTU).
When a black hole is detected in the SEARCHING state, this causes When a black hole is detected in the SEARCHING state, this causes
the PL sender to enter the BASE state. the PL sender to enter the BASE state.
SEARCH_COMPLETE: The SEARCH_COMPLETE state indicates a successful SEARCH_COMPLETE: The SEARCH_COMPLETE state indicates a successful
end to the SEARCHING state. DPLPMTUD remains in this state until end to the SEARCHING state. DPLPMTUD remains in this state until
either the PMTU_RAISE_TIMER expires or a black hole is detected. either the PMTU_RAISE_TIMER expires or a black hole is detected.
When DPLPMTUD uses an unacknowledged PL and is in the When DPLPMTUD uses an unacknowledged PL and is in the
SEARCH_COMPLETE state, a CONFIRMATION_TIMER periodically resets SEARCH_COMPLETE state, a CONFIRMATION_TIMER periodically resets
the PROBE_COUNT and schedules a probe packet with the size of the the PROBE_COUNT and schedules a probe packet with the size of the
PLPMTU. If MAX_PROBES successive PLPMTUD sized probes fail to be PLPMTU. If MAX_PROBES successive PLPMTUD sized probes fail to be
acknowledged the method enters the BASE state. When used with an acknowledged the method enters the BASE state. When used with an
acknowledged PL (e.g., SCTP), DPLPMTUD SHOULD NOT continue to acknowledged PL (e.g., SCTP), DPLPMTUD SHOULD NOT continue to
generate PLPMTU probes in this state. generate PLPMTU probes in this state.
ERROR: The ERROR state represents the case where either the network ERROR: The ERROR state represents the case where either the network
path is not known to support a PLPMTU of at least the BASE_PMTU path is not known to support a PLPMTU of at least the BASE_PLPMTU
size or when there is contradictory information about the network size or when there is contradictory information about the network
path that would otherwise result in excessive variation in the MPS path that would otherwise result in excessive variation in the MPS
signalled to the higher layer. The state implements a method to signaled to the higher layer. The state implements a method to
mitigate oscillation in the state-event engine. It signals a mitigate oscillation in the state-event engine. It signals a
conservative value of the MPS to the higher layer by the PL. The conservative value of the MPS to the higher layer by the PL. The
state is exited when packet probes no longer detect the error. state is exited when packet probes no longer detect the error.
The PL sender then enters the SEARCHING state. The PL sender then enters the SEARCHING state.
Implementations are permitted to enable endpoint fragmentation if Implementations are permitted to enable endpoint fragmentation if
the DPLPMTUD is unable to validate MIN_PMTU within PROBE_COUNT the DPLPMTUD is unable to validate MIN_PLPMTU within PROBE_COUNT
probes. If DPLPMTUD is unable to validate MIN_PMTU the probes. If DPLPMTUD is unable to validate MIN_PLPMTU the
implementation will transition to the DISABLED state. implementation will transition to the DISABLED state.
Note: MIN_PMTU could be identical to BASE_PMTU, simplifying the Note: MIN_PLPMTU could be identical to BASE_PLPMTU, simplifying
actions in this state. the actions in this state.
5.3. Search to Increase the PLPMTU 5.3. Search to Increase the PLPMTU
This section describes the algorithms used by DPLPMTUD to search for This section describes the algorithms used by DPLPMTUD to search for
a larger PLPMTU. a larger PLPMTU.
5.3.1. Probing for a larger PLPMTU 5.3.1. Probing for a larger PLPMTU
Implementations use a search algorithm across the search range to Implementations use a search algorithm across the search range to
determine whether a larger PLPMTU can be supported across a network determine whether a larger PLPMTU can be supported across a network
path. path.
The method discovers the search range by confirming the minimum The method discovers the search range by confirming the minimum
PLPMTU and then using the probe method to select a PROBED_SIZE less PLPMTU and then using the probe method to select a PROBED_SIZE less
than or equal to MAX_PMTU. MAX_PMTU is the minimum of the local MTU than or equal to MAX_PLPMTU. MAX_PLPMTU is the minimum of the local
and EMTU_R (learned from the remote endpoint). The MAX_PMTU MAY be MTU and EMTU_R (when this is learned from the remote endpoint). The
reduced by an application that sets a maximum to the size of MAX_PLPMTU MAY be reduced by an application that sets a maximum to
datagrams it will send. the size of datagrams it will send.
The PROBE_COUNT is initialized to zero when the first probe with a The PROBE_COUNT is initialized to zero when the first probe with a
size greater than or equal to PLPMTUD is sent. A timer is used to size greater than or equal to PLPMTUD is sent. A timer is used to
trigger the sending of probe packets of size PROBED_SIZE, larger than trigger the sending of probe packets of size PROBED_SIZE, larger than
the PLPMTU. Each probe packet successfully sent to the remote peer the PLPMTU. Each probe packet successfully sent to the remote peer
is confirmed by acknowledgement at the PL, see Section 4.1. is confirmed by acknowledgment at the PL, see Section 4.1.
Each time a probe packet is sent to the destination, the PROBE_TIMER Each time a probe packet is sent to the destination, the PROBE_TIMER
is started. The timer is canceled when the PL receives is started. The timer is canceled when the PL receives
acknowledgment that the probe packet has been successfully sent acknowledgment that the probe packet has been successfully sent
across the path Section 4.1. This confirms that the PROBED_SIZE is across the path Section 4.1. This confirms that the PROBED_SIZE is
supported, and the PROBED_SIZE value is then assigned to the PLPMTU. supported, and the PROBED_SIZE value is then assigned to the PLPMTU.
The search algorithm can continue to send subsequent probe packets of The search algorithm can continue to send subsequent probe packets of
an increasing size. an increasing size.
If the timer expires before a probe packet is acknowledged, the probe If the timer expires before a probe packet is acknowledged, the probe
skipping to change at page 29, line 9 skipping to change at page 30, line 9
A PL sender is able to detect inconsistency from the sequence of A PL sender is able to detect inconsistency from the sequence of
PLPMTU probes that are acknowledged or the sequence of PTB messages PLPMTU probes that are acknowledged or the sequence of PTB messages
that it receives. When inconsistent path information is detected, a that it receives. When inconsistent path information is detected, a
PL sender could use an alternate search mode that clamps the offered PL sender could use an alternate search mode that clamps the offered
MPS to a smaller value for a period of time. This avoids unnecessary MPS to a smaller value for a period of time. This avoids unnecessary
loss of packets. loss of packets.
5.4. Robustness to Inconsistent Paths 5.4. Robustness to Inconsistent Paths
Some paths could be unable to sustain packets of the BASE_PMTU size. Some paths could be unable to sustain packets of the BASE_PLPMTU
To be robust to these paths an implementation could implement the size. To be robust to these paths an implementation could implement
Error State. This allows fallback to a smaller than desired PLPMTU, the Error State. This allows fallback to a smaller than desired
rather than suffer connectivity failure. This could utilize methods PLPMTU, rather than suffer connectivity failure. This could utilize
such as endpoint IP fragmentation to enable the PL sender to methods such as endpoint IP fragmentation to enable the PL sender to
communicate using packets smaller than the BASE_PMTU. communicate using packets smaller than the BASE_PLPMTU.
6. Specification of Protocol-Specific Methods 6. Specification of Protocol-Specific Methods
DPLPMTUD requires protocol-specific details to be specified for each DPLPMTUD requires protocol-specific details to be specified for each
PL that is used. PL that is used.
The first subsection provides guidance on how to implement the The first subsection provides guidance on how to implement the
DPLPMTUD method as a part of an application using UDP or UDP-Lite. DPLPMTUD method as a part of an application using UDP or UDP-Lite.
The guidance also applies to other datagram services that do not The guidance also applies to other datagram services that do not
include a specific transport protocol (such as a tunnel include a specific transport protocol (such as a tunnel
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In addition, it is desirable that PMTU discovery is not performed by In addition, it is desirable that PMTU discovery is not performed by
multiple protocol layers. An application SHOULD avoid using DPLPMTUD multiple protocol layers. An application SHOULD avoid using DPLPMTUD
when the underlying transport system provides this capability. To when the underlying transport system provides this capability. To
use common method for managing the PLPMTU has benefits, both in the use common method for managing the PLPMTU has benefits, both in the
ability to share state between different processes and opportunities ability to share state between different processes and opportunities
to coordinate probing. to coordinate probing.
6.1.1. Application Request 6.1.1. Application Request
An application needs an application-layer protocol mechanism (such as An application needs an application-layer protocol mechanism (such as
a message acknowledgement method) that solicits a response from a a message acknowledgment method) that solicits a response from a
destination endpoint. The method SHOULD allow the sender to check destination endpoint. The method SHOULD allow the sender to check
the value returned in the response to provide additional protection the value returned in the response to provide additional protection
from off-path insertion of data [RFC8085], suitable methods include a from off-path insertion of data [RFC8085], suitable methods include a
parameter known only to the two endpoints, such as a session ID or parameter known only to the two endpoints, such as a session ID or
initialized sequence number. initialized sequence number.
6.1.2. Application Response 6.1.2. Application Response
An application needs an application-layer protocol mechanism to An application needs an application-layer protocol mechanism to
communicate the response from the destination endpoint. This communicate the response from the destination endpoint. This
response could indicate successful reception of the probe across the response could indicate successful reception of the probe across the
path, but could also indicate that some (or all packets) have failed path, but could also indicate that some (or all packets) have failed
to reach the destination. to reach the destination.
6.1.3. Sending Application Probe Packets 6.1.3. Sending Application Probe Packets
A probe packet that could carry an application data block, but the A probe packet can carry an application data block, but the
successful transmission of this data is at risk when used for successful transmission of this data is at risk when used for
probing. Some applications might prefer to use a probe packet that probing. Some applications might prefer to use a probe packet that
does not carry an application data block to avoid disruption to data does not carry an application data block to avoid disruption to data
transfer. transfer.
6.1.4. Initial Connectivity 6.1.4. Initial Connectivity
An application that does not have other higher-layer information An application that does not have other higher-layer information
confirming connectivity with the remote peer SHOULD implement a confirming connectivity with the remote peer SHOULD implement a
connectivity mechanism using acknowledged probe packets before connectivity mechanism using acknowledged probe packets before
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An application that does not have other higher-layer information An application that does not have other higher-layer information
confirming correct delivery of datagrams SHOULD implement the confirming correct delivery of datagrams SHOULD implement the
CONFIRMATION_TIMER to periodically send probe packets while in the CONFIRMATION_TIMER to periodically send probe packets while in the
SEARCH_COMPLETE state. SEARCH_COMPLETE state.
6.1.6. Handling of PTB Messages 6.1.6. Handling of PTB Messages
An application that is able and wishes to receive PTB messages MUST An application that is able and wishes to receive PTB messages MUST
perform ICMP validation as specified in Section 5.2 of [RFC8085]. perform ICMP validation as specified in Section 5.2 of [RFC8085].
This requires that the application to check each received PTB This requires that the application checks each received PTB message
messages to validate it is received in response to transmitted to validate that it was is received in response to transmitted
traffic and that the reported PTB_SIZE is less than the current traffic and that the reported PL_PTB_SIZE is less than the current
probed size (see Section 4.6.2). A validated PTB message MAY be used probed size (see Section 4.6.2). A validated PTB message MAY be used
as input to the DPLPMTUD algorithm, but MUST NOT be used directly to as input to the DPLPMTUD algorithm, but MUST NOT be used directly to
set the PLPMTU. set the PLPMTU.
6.2. DPLPMTUD for SCTP 6.2. DPLPMTUD for SCTP
Section 10.2 of [RFC4821] specified a recommended PLPMTUD probing Section 10.2 of [RFC4821] specified a recommended PLPMTUD probing
method for SCTP and Section 7.3 of [RFC4960] and recommended an method for SCTP and Section 7.3 of [RFC4960] and recommended an
endpoint apply the techniques in RFC4821 on a per-destination-address endpoint apply the techniques in RFC4821 on a per-destination-address
basis. The specification for DPLPMTUD continues the practice of basis. The specification for DPLPMTUD continues the practice of
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The HEARTBEAT chunk carries a Heartbeat Information parameter which The HEARTBEAT chunk carries a Heartbeat Information parameter which
includes, besides the information suggested in [RFC4960], the probe includes, besides the information suggested in [RFC4960], the probe
size, which is the size of the complete datagram. The size of the size, which is the size of the complete datagram. The size of the
PAD chunk is therefore computed by reducing the probing size by the PAD chunk is therefore computed by reducing the probing size by the
IPv4 or IPv6 header size, the SCTP common header, the HEARTBEAT IPv4 or IPv6 header size, the SCTP common header, the HEARTBEAT
request and the PAD chunk header. The payload of the PAD chunk request and the PAD chunk header. The payload of the PAD chunk
contains arbitrary data. contains arbitrary data.
Probing starts directly after the PL handshake, before data is sent. Probing starts directly after the PL handshake, before data is sent.
Assuming this behavior (i.e., the PMTU is smaller than or equal to Assuming this behavior (i.e., the PMTU is smaller than or equal to
the interface MTU), this process will take a few round trip time the interface MTU), this process will take several round trip time
periods, dependent on the number of PMTU probes sent. The Heartbeat periods, dependent on the number of DPLPMTUD probes sent. The
timer can be used to implement the PROBE_TIMER. Heartbeat timer can be used to implement the PROBE_TIMER.
6.2.1.3. Validating the Path with SCTP 6.2.1.3. Validating the Path with SCTP
Since SCTP provides an acknowledged PL, a sender MUST NOT implement Since SCTP provides an acknowledged PL, a sender MUST NOT implement
the CONFIRMATION_TIMER while in the SEARCH_COMPLETE state. the CONFIRMATION_TIMER while in the SEARCH_COMPLETE state.
6.2.1.4. PTB Message Handling by SCTP 6.2.1.4. PTB Message Handling by SCTP
Normal ICMP validation MUST be performed as specified in Appendix C Normal ICMP validation MUST be performed as specified in Appendix C
of [RFC4960]. This requires that the first 8 bytes of the SCTP of [RFC4960]. This requires that the first 8 bytes of the SCTP
common header are quoted in the payload of the PTB message, which can common header are quoted in the payload of the PTB message, which can
be the case for ICMPv4 and is normally the case for ICMPv6. be the case for ICMPv4 and is normally the case for ICMPv6.
When a PTB message has been validated, the PTB_SIZE reported in the When a PTB message has been validated, the PL_PTB_SIZE calculated
PTB message SHOULD be used with the DPLPMTUD algorithm, providing from the PTB_SIZE reported in the PTB message SHOULD be used with the
that the reported PTB_SIZE is less than the current probe size (see DPLPMTUD algorithm, providing that the reported PL_PTB_SIZE is less
Section 4.6). than the current probe size (see Section 4.6).
6.2.2. DPLPMTUD for SCTP/UDP 6.2.2. DPLPMTUD for SCTP/UDP
The UDP encapsulation of SCTP is specified in [RFC6951]. The UDP encapsulation of SCTP is specified in [RFC6951].
This specification updates the reference to RFC 4821 in section 5.6 This specification updates the reference to RFC 4821 in section 5.6
of RFC 6951 to refer to XXXTHISRFCXXX. RFC 6951 is updated by of RFC 6951 to refer to XXXTHISRFCXXX. RFC 6951 is updated by
addition of the following sentence is to be added at the end of addition of the following sentence is to be added at the end of
section 5.6: "The RECOMMENDED method for determining the MTU of the section 5.6: "The RECOMMENDED method for determining the MTU of the
path is specified in XXXTHISRFCXXX". path is specified in XXXTHISRFCXXX".
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Since SCTP provides an acknowledged PL, a sender MUST NOT implement Since SCTP provides an acknowledged PL, a sender MUST NOT implement
the CONFIRMATION_TIMER while in the SEARCH_COMPLETE state. the CONFIRMATION_TIMER while in the SEARCH_COMPLETE state.
6.2.2.4. Handling of PTB Messages by SCTP/UDP 6.2.2.4. Handling of PTB Messages by SCTP/UDP
ICMP validation MUST be performed for PTB messages as specified in ICMP validation MUST be performed for PTB messages as specified in
Appendix C of [RFC4960]. This requires that the first 8 bytes of the Appendix C of [RFC4960]. This requires that the first 8 bytes of the
SCTP common header are contained in the PTB message, which can be the SCTP common header are contained in the PTB message, which can be the
case for ICMPv4 (but note the UDP header also consumes a part of the case for ICMPv4 (but note the UDP header also consumes a part of the
quoted packet header) and is normally the case for ICMPv6. When the quoted packet header) and is normally the case for ICMPv6. When the
validation is completed, the PTB_SIZE indicated in the PTB message validation is completed, the PL_PTB_SIZE calculated from the PTB_SIZE
SHOULD be used with the DPLPMTUD providing that the reported PTB_SIZE in the PTB message SHOULD be used with the DPLPMTUD providing that
is less than the current probe size. the reported PL_PTB_SIZE is less than the current probe size.
6.2.3. DPLPMTUD for SCTP/DTLS 6.2.3. DPLPMTUD for SCTP/DTLS
The Datagram Transport Layer Security (DTLS) encapsulation of SCTP is The Datagram Transport Layer Security (DTLS) encapsulation of SCTP is
specified in [RFC8261] . This is used for data channels in WebRTC specified in [RFC8261]. This is used for data channels in WebRTC
implementations. This specification updates the reference to RFC implementations. This specification updates the reference to RFC
4821 in section 5 of RFC 8261 to refer to XXXTHISRFCXXX. 4821 in section 5 of RFC 8261 to refer to XXXTHISRFCXXX.
XXX RFC EDITOR - please replace XXXTHISRFCXXX when published XXX XXX RFC EDITOR - please replace XXXTHISRFCXXX when published XXX
6.2.3.1. Initial Connectivity 6.2.3.1. Initial Connectivity
A sender can enter the BASE state as soon as SCTP connectivity has A sender can enter the BASE state as soon as SCTP connectivity has
been confirmed. been confirmed.
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QUIC [I-D.ietf-quic-transport] is a UDP-based transport that provides QUIC [I-D.ietf-quic-transport] is a UDP-based transport that provides
reception feedback. The UDP payload includes the QUIC packet header, reception feedback. The UDP payload includes the QUIC packet header,
protected payload, and any authentication fields. QUIC depends on a protected payload, and any authentication fields. QUIC depends on a
PMTU of at least 1280 bytes. PMTU of at least 1280 bytes.
Section 14 of [I-D.ietf-quic-transport] describes the path Section 14 of [I-D.ietf-quic-transport] describes the path
considerations when sending QUIC packets. It recommends the use of considerations when sending QUIC packets. It recommends the use of
PADDING frames to build the probe packet. Pure probe-only packets PADDING frames to build the probe packet. Pure probe-only packets
are constructed with PADDING frames and PING frames to create a are constructed with PADDING frames and PING frames to create a
padding only packet that will elicit an acknowledgement. Such padding only packet that will elicit an acknowledgment. Such padding
padding only packets enable probing without affecting the transfer of only packets enable probing without affecting the transfer of other
other QUIC frames. QUIC frames.
The recommendation for QUIC endpoints implementing DPLPMTUD is that a The recommendation for QUIC endpoints implementing DPLPMTUD is that a
MPS is maintained for each combination of local and remote IP MPS is maintained for each combination of local and remote IP
addresses [I-D.ietf-quic-transport]. If a QUIC endpoint determines addresses [I-D.ietf-quic-transport]. If a QUIC endpoint determines
that the PMTU between any pair of local and remote IP addresses has that the PMTU between any pair of local and remote IP addresses has
fallen below an acceptable MPS, it immediately ceases to send QUIC fallen below the size required for an acceptable MPS, it immediately
packets on the affected path. This could result in termination of ceases to send QUIC packets on the affected path. This could result
the connection if an alternative path cannot be found in termination of the connection if an alternative path cannot be
[I-D.ietf-quic-transport]. found [I-D.ietf-quic-transport].
6.3.1. Initial Connectivity 6.3.1. Initial Connectivity
The base protocol is specified in [I-D.ietf-quic-transport]. This The base protocol is specified in [I-D.ietf-quic-transport]. This
provides an acknowledged PL. A sender can therefore enter the BASE provides an acknowledged PL. A sender can therefore enter the BASE
state as soon as connectivity has been confirmed. state as soon as connectivity has been confirmed.
6.3.2. Sending QUIC Probe Packets 6.3.2. Sending QUIC Probe Packets
A probe packet consists of a QUIC Header and a payload containing A probe packet consists of a QUIC Header and a payload containing
PADDING Frames and a PING Frame. PADDING Frames are a single octet PADDING Frames and a PING Frame. PADDING Frames are a single octet
(0x00) and several of these can be used to create a probe packet of (0x00) and several of these can be used to create a probe packet of
size PROBED_SIZE. QUIC provides an acknowledged PL, a sender can size PROBED_SIZE. QUIC provides an acknowledged PL, a sender can
therefore enter the BASE state as soon as connectivity has been therefore enter the BASE state as soon as connectivity has been
confirmed. confirmed.
The current specification of QUIC sets the following: The current specification of QUIC sets the following:
* BASE_PMTU: 1280. A QUIC sender pads initial packets to confirm * BASE_PLPMTU: A QUIC sender pads initial packets to confirm the
the path can support packets of the required size. path can support packets of the required size, this sets the
BASE_PLPMTU and MIN_PLPMTU.
* MIN_PMTU: 1280 bytes. A QUIC sender that determines the PLPMTU * MIN_PLPMTU: A QUIC sender that determines the MIN_PLPMTU has
has fallen below 1280 bytes MUST immediately stop sending on the fallen MUST immediately stop sending on the affected path.
affected path.
6.3.3. Validating the Path with QUIC 6.3.3. Validating the Path with QUIC
QUIC provides an acknowledged PL. A sender therefore MUST NOT QUIC provides an acknowledged PL. A sender therefore MUST NOT
implement the CONFIRMATION_TIMER while in the SEARCH_COMPLETE state. implement the CONFIRMATION_TIMER while in the SEARCH_COMPLETE state.
6.3.4. Handling of PTB Messages by QUIC 6.3.4. Handling of PTB Messages by QUIC
QUIC validates ICMP PTB messages. In addition to UDP Port QUIC validates ICMP PTB messages. In addition to UDP Port
validation, QUIC can validate an ICMP message by using other PL validation, QUIC can validate an ICMP message by using other PL
information (e.g., validation of connection IDs in the quoted packet information (e.g., validation of connection identifiers (CIDs) in the
of any received ICMP message). quoted packet of any received ICMP message).
7. Acknowledgements 7. Acknowledgments
This work was partially funded by the European Union's Horizon 2020 This work was partially funded by the European Union's Horizon 2020
research and innovation programme under grant agreement No. 644334 research and innovation programme under grant agreement No. 644334
(NEAT). The views expressed are solely those of the author(s). (NEAT). The views expressed are solely those of the author(s).
Thanks to all that have commented or contributed, the TSVWG and QUIC Thanks to all that have commented or contributed, the TSVWG and QUIC
working groups, and Mathew Calder and Julius Flohr for providing working groups, and Mathew Calder and Julius Flohr for providing
early implementations. early implementations.
8. IANA Considerations 8. IANA Considerations
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hole data by indicating a size larger than supported by the path. hole data by indicating a size larger than supported by the path.
Parallel forwarding paths SHOULD be considered. Section 5.4 Parallel forwarding paths SHOULD be considered. Section 5.4
identifies the need for robustness in the method because the path identifies the need for robustness in the method because the path
information might be inconsistent. information might be inconsistent.
A node performing DPLPMTUD could experience conflicting information A node performing DPLPMTUD could experience conflicting information
about the size of supported probe packets. This could occur when about the size of supported probe packets. This could occur when
there are multiple paths are concurrently in use and these exhibit a there are multiple paths are concurrently in use and these exhibit a
different PMTU. If not considered, this could result in packets not different PMTU. If not considered, this could result in packets not
being delivered (black holed) when the PLPMTU is larger than the being delivered (black holed) when the PLPMTU results in a packet
smallest actual PMTU. larger than the smallest actual PMTU.
DPLPMTUD methods can introduce padding data to inflate the length of DPLPMTUD methods can introduce padding data to inflate the length of
the datagram to the total size required for a probe packet. The the datagram to the total size required for a probe packet. The
total size of a probe packet includes all headers and padding added total size of a probe packet includes all headers and padding added
to the payload data being sent (e.g., including security-related to the payload data being sent (e.g., including security-related
fields such as an AEAD tag and TLS record layer padding). The value fields such as an AEAD tag and TLS record layer padding). The value
of the padding data does not influence the DPLPMTUD search algorithm, of the padding data does not influence the DPLPMTUD search algorithm,
and therefore needs to be set consistent with the policy of the PL. and therefore needs to be set consistent with the policy of the PL.
If a PL can make use of cryptographic confidentiality or data- If a PL can make use of cryptographic confidentiality or data-
integrity mechanisms, then adding anything (e.g., padding) for integrity mechanisms, then the design ought to avoid adding anything
DPLPMTUD that is not protected by those cryptographic mechanisms is (e.g., padding) to DPLPMTUD probe packets that is not also protected
an anti-pattern to be avoided. by those cryptographic mechanisms.
10. References 10. References
10.1. Normative References 10.1. Normative References
[I-D.ietf-quic-transport] [I-D.ietf-quic-transport]
Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
and Secure Transport", Work in Progress, Internet-Draft, and Secure Transport", Work in Progress, Internet-Draft,
draft-ietf-quic-transport-27, 21 February 2020, draft-ietf-quic-transport-27, 21 February 2020,
<http://www.ietf.org/internet-drafts/draft-ietf-quic- <http://www.ietf.org/internet-drafts/draft-ietf-quic-
skipping to change at page 42, line 51 skipping to change at page 44, line 4
* Removed section on DPLPMTUD with UDP Options. * Removed section on DPLPMTUD with UDP Options.
* Shortened the description of phases. * Shortened the description of phases.
Working group draft -09: Working group draft -09:
* Remove final mention of UDP Options * Remove final mention of UDP Options
* Add Initial Connectivity sections to each PL * Add Initial Connectivity sections to each PL
* Add to disable outgoing pmtu enforcement of packets * Add to disable outgoing pmtu enforcement of packets
Working group draft -10: Working group draft -10:
* Address comments from Lars Eggert * Address comments from Lars Eggert
* Reinforce that PROBE_COUNT is successive attempts to probe for any * Reinforce that PROBE_COUNT is successive attempts to probe for any
size size
* Redefine MAx_PROBES to 3 * Redefine MAX_PROBES to 3
* Address PTB_SIZE of 0 or less that MIN_PMTU * Address PTB_SIZE of 0 or less that MIN_PLPMTU
Working group draft -11: Working group draft -11:
* Restore a sentence removed in previous rev * Restore a sentence removed in previous rev
* De-acronymise QUIC * De-acronymise QUIC
* Address some nits * Address some nits
Working group draft -12: Working group draft -12:
* Add TSVWG, QUIC and implementers to acknowledgements * Add TSVWG, QUIC and implementers to acknowledgments
* Shorten a diagram line. * Shorten a diagram line.
* Address nits from Julius and Wes. * Address nits from Julius and Wes.
* Be clearer when talking about IP layer caches * Be clearer when talking about IP layer caches
Working group draft -13, -14:
* Updated after WGLC.
Working group draft -15:
* Updated after AD evaluation and prepared for IETF-LC.
Working group draft -16:
* Updated text after SECDIR review.
Working group draft -17:
* Updated text after GENART and IETF-LC.
* Renamed BASE_MTU to BASE_PLPMTU, and MIN and MAX PMTU to PLPMTU
(because these are about a base for the PLPMTU), and ensured
consistent separation of PMTU and PLPMTU.
* Adopted US-style English throughout.
Authors' Addresses Authors' Addresses
Godred Fairhurst Godred Fairhurst
University of Aberdeen University of Aberdeen
School of Engineering School of Engineering
Fraser Noble Building Fraser Noble Building
Aberdeen Aberdeen
AB24 3UE AB24 3UE
United Kingdom United Kingdom
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