draft-ietf-tsvwg-datagram-plpmtud-19.txt		draft-ietf-tsvwg-datagram-plpmtud-20.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: 5 October 2020 T. Voelker		Expires: 8 November 2020 T. Voelker
	Muenster University of Applied Sciences		Muenster University of Applied Sciences
	3 April 2020		7 May 2020
	Packetization Layer Path MTU Discovery for Datagram Transports		Packetization Layer Path MTU Discovery for Datagram Transports
	draft-ietf-tsvwg-datagram-plpmtud-19		draft-ietf-tsvwg-datagram-plpmtud-20
	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
	black hole (where packets are discarded). The method can probe a		black hole (where packets are discarded). The method can probe a
	network path with progressively larger packets to discover whether		network path with progressively larger packets to discover whether
	the maximum packet size can be increased. This allows a sender to		the maximum packet size can be increased. This allows a sender to
	determine an appropriate packet size, providing functionality for		determine an appropriate packet size, providing functionality for
	datagram transports that is equivalent to the Packetization Layer		datagram transports that is equivalent to the Packetization Layer
	PMTUD specification for TCP, specified in RFC 4821.		PMTUD specification for TCP, specified in RFC 4821.
	This document updates RFC 4821 to specify the method for datagram		This document updates RFC 4821 to specify the PLPMTUD method for
	PLs, and updates RFC 8085 as the method to use in place of RFC 4821		datagram PLs. It also updates RFC 8085 to refer to the method
	with UDP datagrams. Section 7.3 of RFC4960 recommends an endpoint		specified in this document instead of the method in RFC 4821 for use
			with UDP datagrams. Section 7.3 of RFC 4960 recommends an endpoint
	apply the techniques in RFC 4821 on a per-destination-address basis.		apply the techniques in RFC 4821 on a per-destination-address basis.
	RFC 4960, RFC 6951 and RFC 8261 are updated to recommend that SCTP,		RFC 4960, RFC 6951, and RFC 8261 are updated to recommend that SCTP,
	SCTP encapsulated in UDP and SCTP encapsulated in DTLS use the method		SCTP encapsulated in UDP and SCTP encapsulated in DTLS use the method
	specified in this document instead of the method in RFC 4821.		specified in this document instead of the method in RFC 4821.
	The document also provides implementation notes for incorporating		The document also provides implementation notes for incorporating
	Datagram PMTUD into IETF datagram transports or applications that use		Datagram PMTUD into IETF datagram transports or applications that use
	datagram transports.		datagram transports.
	When published, this specification updates RFC 4960, RFC 4821, RFC		When published, this specification updates RFC 4960, RFC 4821, RFC
	8085 and RFC 8261.		8085 and RFC 8261.
	skipping to change at page 2, line 15 ¶		skipping to change at page 2, line 20 ¶
	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 5 October 2020.		This Internet-Draft will expire on 8 November 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 42 ¶		skipping to change at page 2, line 47 ¶
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
	1.1. Classical Path MTU Discovery . . . . . . . . . . . . . . 4		1.1. Classical Path MTU Discovery . . . . . . . . . . . . . . 4
	1.2. Packetization Layer Path MTU Discovery . . . . . . . . . 6		1.2. Packetization Layer Path MTU Discovery . . . . . . . . . 6
	1.3. Path MTU Discovery for Datagram Services . . . . . . . . 7		1.3. Path MTU Discovery for Datagram Services . . . . . . . . 7
	2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 8		2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 8
	3. Features Required to Provide Datagram PLPMTUD . . . . . . . . 11		3. Features Required to Provide Datagram PLPMTUD . . . . . . . . 11
	4. DPLPMTUD Mechanisms . . . . . . . . . . . . . . . . . . . . . 14		4. DPLPMTUD Mechanisms . . . . . . . . . . . . . . . . . . . . . 14
	4.1. PLPMTU Probe Packets . . . . . . . . . . . . . . . . . . 14		4.1. PLPMTU Probe Packets . . . . . . . . . . . . . . . . . . 14
	4.2. Confirmation of Probed Packet Size . . . . . . . . . . . 15		4.2. Confirmation of Probed Packet Size . . . . . . . . . . . 15
	4.3. Black Hole Detection and Reducing the PLPMTU . . . . . . 15		4.3. Black Hole Detection and Reducing the PLPMTU . . . . . . 16
	4.4. The Maximum Packet Size (MPS) . . . . . . . . . . . . . . 16		4.4. The Maximum Packet Size (MPS) . . . . . . . . . . . . . . 17
	4.5. Disabling the Effect of PMTUD . . . . . . . . . . . . . . 17		4.5. Disabling the Effect of PMTUD . . . . . . . . . . . . . . 18
	4.6. Response to PTB Messages . . . . . . . . . . . . . . . . 18		4.6. Response to PTB Messages . . . . . . . . . . . . . . . . 18
	4.6.1. Validation of PTB Messages . . . . . . . . . . . . . 18		4.6.1. Validation of PTB Messages . . . . . . . . . . . . . 18
	4.6.2. Use of PTB Messages . . . . . . . . . . . . . . . . . 19		4.6.2. Use of PTB Messages . . . . . . . . . . . . . . . . . 19
	5. Datagram Packetization Layer PMTUD . . . . . . . . . . . . . 20		5. Datagram Packetization Layer PMTUD . . . . . . . . . . . . . 20
	5.1. DPLPMTUD Components . . . . . . . . . . . . . . . . . . . 21		5.1. DPLPMTUD Components . . . . . . . . . . . . . . . . . . . 21
	5.1.1. Timers . . . . . . . . . . . . . . . . . . . . . . . 21		5.1.1. Timers . . . . . . . . . . . . . . . . . . . . . . . 21
	5.1.2. Constants . . . . . . . . . . . . . . . . . . . . . . 22		5.1.2. Constants . . . . . . . . . . . . . . . . . . . . . . 22
	5.1.3. Variables . . . . . . . . . . . . . . . . . . . . . . 23		5.1.3. Variables . . . . . . . . . . . . . . . . . . . . . . 23
	5.1.4. Overview of DPLPMTUD Phases . . . . . . . . . . . . . 24		5.1.4. Overview of DPLPMTUD Phases . . . . . . . . . . . . . 24
	5.2. State Machine . . . . . . . . . . . . . . . . . . . . . . 26		5.2. State Machine . . . . . . . . . . . . . . . . . . . . . . 26
	5.3. Search to Increase the PLPMTU . . . . . . . . . . . . . . 29		5.3. Search to Increase the PLPMTU . . . . . . . . . . . . . . 29
	5.3.1. Probing for a larger PLPMTU . . . . . . . . . . . . . 29		5.3.1. Probing for a larger PLPMTU . . . . . . . . . . . . . 29
	5.3.2. Selection of Probe Sizes . . . . . . . . . . . . . . 30		5.3.2. Selection of Probe Sizes . . . . . . . . . . . . . . 30
	skipping to change at page 3, line 18 ¶		skipping to change at page 3, line 24 ¶
	5.3.2. Selection of Probe Sizes . . . . . . . . . . . . . . 30		5.3.2. Selection of Probe Sizes . . . . . . . . . . . . . . 30
	5.3.3. Resilience to Inconsistent Path Information . . . . . 30		5.3.3. Resilience to Inconsistent Path Information . . . . . 30
	5.4. Robustness to Inconsistent Paths . . . . . . . . . . . . 31		5.4. Robustness to Inconsistent Paths . . . . . . . . . . . . 31
	6. Specification of Protocol-Specific Methods . . . . . . . . . 31		6. Specification of Protocol-Specific Methods . . . . . . . . . 31
	6.1. Application support for DPLPMTUD with UDP or UDP-Lite . . 31		6.1. Application support for DPLPMTUD with UDP or UDP-Lite . . 31
	6.1.1. Application Request . . . . . . . . . . . . . . . . . 32		6.1.1. Application Request . . . . . . . . . . . . . . . . . 32
	6.1.2. Application Response . . . . . . . . . . . . . . . . 32		6.1.2. Application Response . . . . . . . . . . . . . . . . 32
	6.1.3. Sending Application Probe Packets . . . . . . . . . . 32		6.1.3. Sending Application Probe Packets . . . . . . . . . . 32
	6.1.4. Initial Connectivity . . . . . . . . . . . . . . . . 32		6.1.4. Initial Connectivity . . . . . . . . . . . . . . . . 32
	6.1.5. Validating the Path . . . . . . . . . . . . . . . . . 32		6.1.5. Validating the Path . . . . . . . . . . . . . . . . . 32
	6.1.6. Handling of PTB Messages . . . . . . . . . . . . . . 33		6.1.6. Handling of PTB Messages . . . . . . . . . . . . . . 32
	6.2. DPLPMTUD for SCTP . . . . . . . . . . . . . . . . . . . . 33		6.2. DPLPMTUD for SCTP . . . . . . . . . . . . . . . . . . . . 33
	6.2.1. SCTP/IPv4 and SCTP/IPv6 . . . . . . . . . . . . . . . 33		6.2.1. SCTP/IPv4 and SCTP/IPv6 . . . . . . . . . . . . . . . 33
	6.2.1.1. Initial Connectivity . . . . . . . . . . . . . . 33		6.2.1.1. Initial Connectivity . . . . . . . . . . . . . . 33
	6.2.1.2. Sending SCTP Probe Packets . . . . . . . . . . . 33		6.2.1.2. Sending SCTP Probe Packets . . . . . . . . . . . 33
	6.2.1.3. Validating the Path with SCTP . . . . . . . . . . 34		6.2.1.3. Validating the Path with SCTP . . . . . . . . . . 34
	6.2.1.4. PTB Message Handling by SCTP . . . . . . . . . . 34		6.2.1.4. PTB Message Handling by SCTP . . . . . . . . . . 34
	6.2.2. DPLPMTUD for SCTP/UDP . . . . . . . . . . . . . . . . 34		6.2.2. DPLPMTUD for SCTP/UDP . . . . . . . . . . . . . . . . 34
	6.2.2.1. Initial Connectivity . . . . . . . . . . . . . . 35		6.2.2.1. Initial Connectivity . . . . . . . . . . . . . . 35
	6.2.2.2. Sending SCTP/UDP Probe Packets . . . . . . . . . 35		6.2.2.2. Sending SCTP/UDP Probe Packets . . . . . . . . . 35
	6.2.2.3. Validating the Path with SCTP/UDP . . . . . . . . 35		6.2.2.3. Validating the Path with SCTP/UDP . . . . . . . . 35
	6.2.2.4. Handling of PTB Messages by SCTP/UDP . . . . . . 35		6.2.2.4. Handling of PTB Messages by SCTP/UDP . . . . . . 35
	6.2.3. DPLPMTUD for SCTP/DTLS . . . . . . . . . . . . . . . 35		6.2.3. DPLPMTUD for SCTP/DTLS . . . . . . . . . . . . . . . 35
	6.2.3.1. Initial Connectivity . . . . . . . . . . . . . . 35		6.2.3.1. Initial Connectivity . . . . . . . . . . . . . . 35
	6.2.3.2. Sending SCTP/DTLS Probe Packets . . . . . . . . . 35		6.2.3.2. Sending SCTP/DTLS Probe Packets . . . . . . . . . 36
	6.2.3.3. Validating the Path with SCTP/DTLS . . . . . . . 36		6.2.3.3. Validating the Path with SCTP/DTLS . . . . . . . 36
	6.2.3.4. Handling of PTB Messages by SCTP/DTLS . . . . . . 36		6.2.3.4. Handling of PTB Messages by SCTP/DTLS . . . . . . 36
	6.3. DPLPMTUD for QUIC . . . . . . . . . . . . . . . . . . . . 36		6.3. DPLPMTUD for QUIC . . . . . . . . . . . . . . . . . . . . 36
	6.3.1. Initial Connectivity . . . . . . . . . . . . . . . . 36		6.3.1. Initial Connectivity . . . . . . . . . . . . . . . . 36
	6.3.2. Sending QUIC Probe Packets . . . . . . . . . . . . . 36		6.3.2. Sending QUIC Probe Packets . . . . . . . . . . . . . 37
	6.3.3. Validating the Path with QUIC . . . . . . . . . . . . 37		6.3.3. Validating the Path with QUIC . . . . . . . . . . . . 37
	6.3.4. Handling of PTB Messages by QUIC . . . . . . . . . . 37		6.3.4. Handling of PTB Messages by QUIC . . . . . . . . . . 37
	7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 37		7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 37
	8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 37		8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 37
	9. Security Considerations . . . . . . . . . . . . . . . . . . . 37		9. Security Considerations . . . . . . . . . . . . . . . . . . . 38
	10. References . . . . . . . . . . . . . . . . . . . . . . . . . 39		10. References . . . . . . . . . . . . . . . . . . . . . . . . . 39
	10.1. Normative References . . . . . . . . . . . . . . . . . . 39		10.1. Normative References . . . . . . . . . . . . . . . . . . 39
	10.2. Informative References . . . . . . . . . . . . . . . . . 40		10.2. Informative References . . . . . . . . . . . . . . . . . 41
	Appendix A. Revision Notes . . . . . . . . . . . . . . . . . . . 42		Appendix A. Revision Notes . . . . . . . . . . . . . . . . . . . 42
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 46		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 46
	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
	skipping to change at page 4, line 38 ¶		skipping to change at page 4, line 39 ¶
	probe packets.		probe packets.
	Packets not intended as probe packets are either fragmented to the		Packets not intended as probe packets are either fragmented to the
	current effective PMTU, or the attempt to send fails with an error		current effective PMTU, or the attempt to send fails with an error
	code. Applications can be provided with a primitive to let them read		code. Applications can be provided with a primitive to let them read
	the Maximum Packet Size (MPS), derived from the current effective		the Maximum Packet Size (MPS), derived from the current effective
	PMTU.		PMTU.
	Classical PMTUD is subject to protocol failures. One failure arises		Classical PMTUD is subject to protocol failures. One failure arises
	when traffic using a packet size larger than the actual PMTU is		when traffic using a packet size larger than the actual PMTU is
	black-holed (all datagrams sent with this size, or larger, are		black-holed (all datagrams larger than the actual PMTU, are
	discarded). This could arise when the PTB messages are not delivered		discarded). This could arise when the PTB messages are not delivered
	back to the sender for some reason (see for example [RFC2923]).		back to the sender for some reason (see for example [RFC2923]).
	Examples where PTB messages are not delivered include:		Examples where PTB messages are not delivered include:
	* The generation of ICMP messages is usually rate limited. This		* The generation of ICMP messages is usually rate limited. This
	could result in no PTB messages being generated to the sender (see		could result in no PTB messages being generated to the sender (see
	section 2.4 of [RFC4443])		section 2.4 of [RFC4443])
	* ICMP messages can be filtered by middleboxes (including firewalls)		* ICMP messages can be filtered by middleboxes (including firewalls)
	[RFC4890]. A stateful firewall could be configured with a policy		[RFC4890]. A firewall could be configured with a policy to block
	to block incoming ICMP messages, which would prevent reception of		incoming ICMP messages, which would prevent reception of PTB
	PTB messages to a sending endpoint behind this firewall.		messages to a sending endpoint behind this firewall.
	* When the router issuing the ICMP message drops a tunneled packet,		* When the router issuing the ICMP message drops a tunneled packet,
	the resulting ICMP message will be directed to the tunnel ingress.		the resulting ICMP message will be directed to the tunnel ingress.
	This tunnel endpoint is responsible for forwarding the ICMP		This tunnel endpoint is responsible for forwarding the ICMP
	message and also processing the quoted packet within the payload		message and also processing the quoted packet within the payload
	field to remove the effect of the tunnel, and return a correctly		field to remove the effect of the tunnel, and return a correctly
	formatted ICMP message to the sender [I-D.ietf-intarea-tunnels].		formatted ICMP message to the sender [I-D.ietf-intarea-tunnels].
	Failure to do this prevents the PTB message reaching the original		Failure to do this prevents the PTB message reaching the original
	sender.		sender.
	skipping to change at page 6, line 51 ¶		skipping to change at page 7, line 6 ¶
	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.
	In contrast to PMTUD, Packetization Layer Path MTU Discovery		In contrast to PMTUD, Packetization Layer Path MTU Discovery
	(PLPMTUD) [RFC4821] introduced a method that does not rely upon		(PLPMTUD) [RFC4821] introduced a method that does not rely upon
	reception and validation of PTB messages. It is therefore more		reception and validation of PTB messages. It is therefore more
	robust than Classical PMTUD. This has become the recommended		robust than Classical PMTUD. This has become the recommended
	approach for implementing discovery of the PMTU [RFC8085].		approach for implementing discovery of the PMTU [BCP145].
	It uses a general strategy where the PL sends probe packets to search		It uses a general strategy where the PL sends probe packets to search
	for the largest size of unfragmented datagram that can be sent over a		for the largest size of unfragmented datagram that can be sent over a
	network path. Probe packets are sent to explore using a larger		network path. Probe packets are sent to explore using a larger
	packet size. If a probe packet is successfully delivered (as		packet size. If a probe packet is successfully delivered (as
	determined by the PL), then the PLPMTU is raised to the size of the		determined by the PL), then the PLPMTU is raised to the size of the
	successful probe. If a black hole is detected (e.g., where packets		successful probe. If a black hole is detected (e.g., where packets
	of size PLPMTU are consistently not received), the method reduces the		of size PLPMTU are consistently not received), the method reduces the
	PLPMTU.		PLPMTU.
	skipping to change at page 7, line 37 ¶		skipping to change at page 7, line 40 ¶
	Section 5 of this document presents a set of algorithms for datagram		Section 5 of this document presents a set of algorithms for datagram
	protocols to discover the largest size of unfragmented datagram that		protocols to discover the largest size of unfragmented datagram that
	can be sent over a network path. The method relies upon features of		can be sent over a network path. The method relies upon features of
	the PL described in Section 3 and applies to transport protocols		the PL described in Section 3 and applies to transport protocols
	operating over IPv4 and IPv6. It does not require cooperation from		operating over IPv4 and IPv6. It does not require cooperation from
	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 [BCP145] 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 MPS (see Section 4.4).		sharing the discovered largest size as the MPS (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 that
	providing a complete specification.		description by 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
	sender "MUST maintain the MPS allowed for each active DCCP session".		sender "MUST maintain the MPS allowed for each active DCCP session".
	It also defines the current congestion control MPS (CCMPS) supported		It also defines the current congestion control MPS (CCMPS) supported
	by a network path. This recommends use of PMTUD, and suggests use of		by a network path. This recommends use of PMTUD, and suggests use of
	control packets (DCCP-Sync) as path probe packets, because they do		control packets (DCCP-Sync) as path probe packets, because they do
	not risk application data loss. The method defined in this		not risk application data loss. The method defined in this
	specification can be used with DCCP.		specification can be used with DCCP.
	skipping to change at page 9, line 50 ¶		skipping to change at page 10, line 6 ¶
	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_PLPMTU: The MAX_PLPMTU is the largest size of PLPMTU that		MAX_PLPMTU: The MAX_PLPMTU is the largest size of PLPMTU that
	DPLPMTUD will attempt to use.		DPLPMTUD will attempt to use (see the constants defined in
			Section 5.1.2).
	MIN_PLPMTU: The MIN_PLPMTU is the smallest size of PLPMTU that		MIN_PLPMTU: The MIN_PLPMTU is the smallest size of PLPMTU that
	DPLPMTUD will attempt to use.		DPLPMTUD will attempt to use (see the constants defined in
			Section 5.1.2).
	MPS: The Maximum Packet Size (MPS) is the largest size of		MPS: The Maximum Packet Size (MPS) is the largest size of
	application data block that can be sent across a network path by a		application data block that can be sent across a network path by a
	PL using a single Datagram.		PL using a single Datagram.
	MSL: Maximum Segment Lifetime (MSL) The maximum delay a packet is		MSL: Maximum Segment Lifetime (MSL) The maximum delay a packet is
	expected to experience across a path, taken as 2 minutes		expected to experience across a path, taken as 2 minutes [BCP145].
	[RFC8085].
	Packet: A Packet is the IP header plus the IP payload.		Packet: A Packet is the IP header(s) and any extension headers/
			options plus the IP payload.
	Packetization Layer (PL): The PL is a layer of the network stack		Packetization Layer (PL): The PL is a layer of the network stack
	that places data into packets and performs transport protocol		that places data into packets and performs transport protocol
	functions. Examples of a PL include: TCP, SCTP, SCTP over DTLS or		functions. Examples of a PL include: TCP, SCTP, SCTP over UDP,
	QUIC.		SCTP over DTLS, or 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, as used by PMTUD.		a destination node, as used by PMTUD.
			PTB: In this document, the term PTB message is applied to both IPv4
			ICMP Unreachable messages (type 3) that carry the error
			Fragmentation Needed (Type 3, Code 4) [RFC0792] and ICMPv6 Packet
			Too Big messages (Type 2) [RFC4443].
	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.
	PL_PTB_SIZE: The size reported in a validated PTB message, reduced		PL_PTB_SIZE: The size reported in a validated PTB message, reduced
	by the size of all headers added by layers below the PL.		by the size of all headers added by layers below the PL.
	PLPMTU: The Packetization Layer PMTU is an estimate of the largest		PLPMTU: The Packetization Layer PMTU is an estimate of the largest
	size of PL datagram that can be sent by a path, controled by		size of PL datagram that can be sent by a path, controled by
	PLPMTUD.		PLPMTUD.
	skipping to change at page 11, line 16 ¶		skipping to change at page 11, line 26 ¶
	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, a datagram PL requires		TCP protocol mechanisms. Unlike TCP, a datagram PL requires
	additional 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. Managing the PLPMTU: For datagram PLs, the PLPMTU is managed by		1. Managing the PLPMTU: For datagram PLs, the PLPMTU is managed by
	DPLPMTUD. A PL MUST NOT send a datagram (other than a probe		DPLPMTUD. A PL MUST NOT send a datagram (other than a probe
	packet) with a size at the PL that is larger than the current		packet) with a size at the PL that is larger than the current
	PLPMTU.		PLPMTU.
	2. Probe packets: The network interface below PL is REQUIRED to
	provide a way to transmit a probe packet that is larger than the
	PLMPMTU. In IPv4, a probe packet MUST be sent with the Don't
	Fragment (DF) bit set in the IP header, and without network
	layer endpoint fragmentation. In IPv6, a probe packet is always
	sent without source fragmentation (as specified in section 5.4
	of [RFC8201]).
	3. Reception feedback: The destination PL endpoint is REQUIRED to
	provide a feedback method that indicates to the DPLPMTUD sender
	when a probe packet has been received by the destination PL
	endpoint. Section 6 provides examples of how a PL can provide
	this acknowledgment of received probe packets.
	4. Probe loss recovery: It is RECOMMENDED to use probe packets that
	do not carry any user data that would require retransmission if
	lost. Most datagram transports permit this. If a probe packet
	contains user data requiring retransmission in case of loss, the
	PL (or layers above) are REQUIRED to arrange any retransmission/
	repair of any resulting loss. The PL is REQUIRED to be robust
	in the case where probe packets are lost due to other reasons
	(including link transmission error, congestion).
	5. PMTU parameters: A DPLPMTUD sender is RECOMMENDED to utilize		2. Probe packets: The network interface below PL is REQUIRED to
	information about the maximum size of packet that can be		provide a way to transmit a probe packet that is larger than the
	transmitted by the sender on the local link (e.g., the local		PLPMTU. In IPv4, a probe packet MUST be sent with the Don't
	Link MTU). It MAY utilize similar information about the maximum		Fragment (DF) bit set in the IP header, and without network layer
	size a receiver can accept when this is supplied (note this		endpoint fragmentation. In IPv6, a probe packet is always sent
	could be less than EMTU_R). This avoids implementations trying		without source fragmentation (as specified in section 5.4 of
	to send probe packets that can not be transferred by the local		[RFC8201]).
	link. Too high of a value could reduce the efficiency of the
	search algorithm. Some applications also have a maximum
	transport protocol data unit (PDU) size, in which case there is
	no benefit from probing for a size larger than this (unless a
	transport allows multiplexing multiple applications PDUs into
	the same datagram).
	6. Processing PTB messages: A DPLPMTUD sender MAY optionally		3. Reception feedback: The destination PL endpoint is REQUIRED to
	utilize PTB messages received from the network layer to help		provide a feedback method that indicates to the DPLPMTUD sender
	identify when a network path does not support the current size		when a probe packet has been received by the destination PL
	of probe packet. Any received PTB message MUST be validated		endpoint. Section 6 provides examples of how a PL can provide
	before it is used to update the PLPMTU discovery information		this acknowledgment of received probe packets.
	[RFC8201]. This validation confirms that the PTB message was
	sent in response to a packet originating by the sender, and
	needs to be performed before the PLPMTU discovery method reacts
	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
	larger PLPMTU. A PL_PTB_SIZE that is greater than that
	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		4. Probe loss recovery: It is RECOMMENDED to use probe packets that
	a probe packet does not need to be limited by the congestion		do not carry any user data that would require retransmission if
	controller. When not controlled by the congestion controller,		lost. Most datagram transports permit this. If a probe packet
	the interval between probe packets MUST be at least one RTT. If		contains user data requiring retransmission in case of loss, the
	transmission of probe packets is limited by the congestion		PL (or layers above) are REQUIRED to arrange any retransmission/
	controller, this could result in transmission of probe packets		repair of any resulting loss. The PL is REQUIRED to be robust in
	being delayed or suspended during congestion.		the case where probe packets are lost due to other reasons
			(including link transmission error, congestion).
	8. Loss of a probe packet SHOULD NOT be treated as an indication of		5. PMTU parameters: A DPLPMTUD sender is RECOMMENDED to utilize
	congestion and SHOULD NOT trigger a congestion control reaction		information about the maximum size of packet that can be
	[RFC4821], because this could result in unnecessary reduction of		transmitted by the sender on the local link (e.g., the local Link
	the sending rate.		MTU). A PL sender MAY utilize similar information about the
			maximum size of network layer packet that a receiver can accept
			when this is supplied (note this could be less than EMTU_R).
			This avoids implementations trying to send probe packets that can
			not be transferred by the local link. Too high of a value could
			reduce the efficiency of the search algorithm. Some applications
			also have a maximum transport protocol data unit (PDU) size, in
			which case there is no benefit from probing for a size larger
			than this (unless a transport allows multiplexing multiple
			applications PDUs into the same datagram).
	9. An update to the PLPMTU (or MPS) MUST NOT increase the		6. Processing PTB messages: A DPLPMTUD sender MAY optionally utilize
	congestion window measured in bytes [RFC4821]. Therefore, an		PTB messages received from the network layer to help identify
	increase in the packet size does not cause an increase in the		when a network path does not support the current size of probe
	data rate in bytes per second.		packet. Any received PTB message MUST be validated before it is
			used to update the PLPMTU discovery information [RFC8201]. This
			validation confirms that the PTB message was sent in response to
			a packet originating by the sender, and needs to be performed
			before the PLPMTU discovery method reacts 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 larger PLPMTU. A valid
			PTB_SIZE is converted to a PL_PTB_SIZE before it is to be used in
			the DPLPMTUD state machine. A PL_PTB_SIZE that is greater than
			that currently probed SHOULD be ignored. (This PTB message ought
			to be discarded without further processing, but could be utilized
			as an input that enables a resilience mode).
	10. A PL that maintains the congestion window in terms of a limit to		7. Probing and congestion control: A PL MAY use a congestion
	the number of outstanding fixed size packets SHOULD adapt this		controller to decide when to send a probe packet. If
	limit to compensate for the size of the actual packets.		transmission of probe packets is limited by the congestion
			controller, this could result in transmission of probe packets
			being delayed or suspended during congestion. When the
			transmission of probe packets is not controlled by the congestion
			controller, the interval between probe packets MUST be at least
			one RTT. Loss of a probe packet SHOULD NOT be treated as an
			indication of congestion and SHOULD NOT trigger a congestion
			control reaction [RFC4821], because this could result in
			unnecessary reduction of the sending rate. An update to the
			PLPMTU (or MPS) MUST NOT increase the congestion window measured
			in bytes [RFC4821]. Therefore, an increase in the packet size
			does not cause an increase in the data rate in bytes per second.
			A PL that maintains the congestion window in terms of a limit to
			the number of outstanding fixed size packets SHOULD adapt this
			limit to compensate for the size of the actual packets. The
			transmission of probe packets can interact with the operation of
			a PL that performs burst mitigation or pacing and could need
			transmission of probe packets to be regulated by these methods.
	11. Probing and flow control: Flow control at the PL concerns the		8. 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. Flow control
	apply to DPLPMTU when probe packets use a design that does not		SHOULD NOT apply to DPLPMTU when probe packets use a design that
	carry user data to the remote application.		does not carry user data to the remote application.
	12. Shared PLPMTU state: The PMTU value calculated from the PLPMTU		9. Shared PLPMTU state: The PMTU value calculated from the PLPMTU
	MAY also be stored with the corresponding entry associated with		MAY also be stored with the corresponding entry associated with
	the destination in the IP layer cache, and used by other PL		the destination in the IP layer cache, and used by other PL
	instances. The specification of PLPMTUD [RFC4821] states: "If		instances. The specification of PLPMTUD [RFC4821] states: "If
	PLPMTUD updates the MTU for a particular path, all Packetization		PLPMTUD updates the MTU for a particular path, all Packetization
	Layer sessions that share the path representation (as described		Layer sessions that share the path representation (as described
	in Section 5.2 of [RFC4821]) SHOULD be notified to make use of		in Section 5.2 of [RFC4821]) SHOULD be notified to make use of
	the new MTU". Such methods MUST be robust to the wide variety		the new MTU". Such methods MUST be robust to the wide variety of
	of underlying network forwarding behaviors. Section 5.2 of		underlying network forwarding behaviors. Section 5.2 of
	[RFC8201] provides guidance on the caching of PMTU information		[RFC8201] provides guidance on the caching of PMTU information
	and also the 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:
	* A PL MAY be designed to segment data blocks larger than the MPS		* A PL MAY be designed to segment data blocks larger than the MPS
	into multiple datagrams. However, not all datagram PLs support		into multiple datagrams. However, not all datagram PLs support
	segmentation of data blocks. It is RECOMMENDED that methods avoid		segmentation of data blocks. It is RECOMMENDED that methods avoid
	forcing an application to use an arbitrary small MPS for		forcing an application to use an arbitrary small MPS for
	transmission while the method is searching for the currently		transmission while the method is searching for the currently
	supported PLPMTU. A reduced MPS can adversely impact the		supported PLPMTU. A reduced MPS can adversely impact the
	skipping to change at page 15, line 8 ¶		skipping to change at page 15, line 21 ¶
	block supplied by an application that matches the size of the		block supplied by an application that matches the size of the
	probe packet. This method requests the application to issue a		probe packet. This method requests the application to issue a
	data block of the desired probe size.		data block of the desired probe size.
	A PL that uses a probe packet carrying application data and needs		A PL that uses a probe packet carrying application data and needs
	protection from the loss of this probe packet could perform		protection from the loss of this probe packet could perform
	transport-layer retransmission/repair of the data block (e.g., by		transport-layer retransmission/repair of the data block (e.g., by
	retransmission after loss is detected or by duplicating the data		retransmission after loss is detected or by duplicating the data
	block in a datagram without the padding data). This retransmitted		block in a datagram without the padding data). This retransmitted
	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 force 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
	PL that can re-segment the data block into multiple datagrams).		fragmentation or a 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 (e.g.,		uniquely identify the probe within Maximum Segment Lifetime (e.g.,
	including a unique identifier from the PL or the DPLPMTUD		including a unique identifier from the PL or the DPLPMTUD
	implementation), while being robust to reordering and replay of probe		implementation), while being robust to reordering and replay of probe
	response and PTB messages.		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,
	SCTP provide keep-alive/heartbeat features). When supported, this		SCTP, and QUIC provide keep-alive/heartbeat features). When
	mechanism MAY also be used by DPLPMTUD to acknowledge reception of a		supported, this mechanism MAY also be used by DPLPMTUD to acknowledge
	probe packet.		reception of a probe packet.
	A PL that does not acknowledge data reception (e.g., UDP and UDP-		A PL that does not acknowledge data reception (e.g., UDP and UDP-
	Lite) is unable itself to detect when the packets that it sends are		Lite) is unable itself to detect when the packets that it sends are
	discarded because their size is greater than the actual PMTU. These		discarded because their size is greater than the actual PMTU. These
	PLs need to rely on an application protocol to detect this loss.		PLs need to rely on an application protocol to detect this loss.
	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 and Reducing the PLPMTU		4.3. Black Hole Detection and Reducing the PLPMTU
	skipping to change at page 17, line 41 ¶		skipping to change at page 17, line 50 ¶
	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 probability of successful 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 utilizing 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.
	skipping to change at page 18, line 29 ¶		skipping to change at page 18, line 38 ¶
	This section specifies utilization and validation of PTB messages.		This section specifies utilization and validation of PTB messages.
	* A simple implementation MAY ignore received PTB messages and in		* A simple implementation MAY ignore received PTB messages and in
	this case the PLPMTU is not updated when a PTB message is		this case the PLPMTU is not updated when a PTB message is
	received.		received.
	* A PL that supports PTB messages MUST validate these messages		* A PL that supports PTB messages MUST validate these messages
	before they are further processed.		before they are further processed.
	A PL that receives a PTB message from a router or middlebox performs		A PL that receives a PTB message from a router or middlebox performs
	ICMP validation as specified in Section 5.2 of [RFC8085][RFC8201].		ICMP validation (see Section 4 of [RFC8201] and Section 5.2 of
	Because DPLPMTUD operates at the PL, the PL needs to check that each		[BCP145]). Because DPLPMTUD operates at the PL, the PL needs to
	received PTB message is received in response to a packet transmitted		check that each received PTB message is received in response to a
	by the endpoint PL performing DPLPMTUD.		packet transmitted by the endpoint PL performing DPLPMTUD.
	The PL MUST check the protocol information in the quoted packet		The PL MUST check the protocol information in the quoted packet
	carried in an ICMP PTB message payload to validate the message		carried in an ICMP PTB message payload to validate the message
	originated from the sending node. This validation includes		originated from the sending node. This validation includes
	determining that the combination of the IP addresses, the protocol,		determining that the combination of the IP addresses, the protocol,
	the source port and destination port match those returned in the		the source port and destination port match those returned in the
	quoted packet - this is also necessary for the PTB message to be		quoted packet - this is also necessary for the PTB message to be
	passed to the corresponding PL.		passed to the corresponding PL.
	The validation SHOULD utilize information that it is not simple for		The validation SHOULD utilize information that it is not simple for
	an off-path attacker to determine [RFC8085]. For example, it could		an off-path attacker to determine [BCP145]. For example, it could
	check the value of a protocol header field known only to the two PL		check the value of a protocol header field known only to the two PL
	endpoints. A datagram application that uses well-known source and		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, as discussed in the Security Considerations		the DPLPMTUD method, as discussed in the Security Considerations
	section.		section.
	PTB messages that have been validated MAY be utilized by the DPLPMTUD		Section 4.6.2 describes this processing of PTB messages.
	algorithm, but MUST NOT be used directly to set the PLPMTU. The
	PL_PTB_SIZE is smaller than the PTB_SIZE because it is reduced by
	headers below the PL including any IP options or extensions added to
	the PL packet. A method that utilizes these PTB messages can improve
	the speed at which the algorithm detects an appropriate PLPMTU by
	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
			PTB messages that have been validated MAY be utilized by the DPLPMTUD
			algorithm, but MUST NOT be used directly to set the PLPMTU.
	Before using the size reported in the PTB message it must first be		Before using the size reported in the PTB message it must first be
	converted to a PL_PTB_SIZE. A set of checks are intended to provide		converted to a PL_PTB_SIZE. The PL_PTB_SIZE is smaller than the
	protection from a router that reports an unexpected PTB_SIZE. The PL		PTB_SIZE because it is reduced by headers below the PL including any
	also needs to check that the indicated PL_PTB_SIZE is less than the		IP options or extensions added to the PL packet.
	size used by probe packets and at least the minimum size accepted.
			A method that utilizes these PTB messages can improve the speed at
			which the algorithm detects an appropriate PLPMTU by 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.
			A set of checks are intended to provide protection from a router that
			reports an unexpected PTB_SIZE. The PL 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 uses the set of constants defined in section 5.1.2). This		(This uses the set of constants defined in Section 5.1.2). This
	processing depends on the PL_PTB_SIZE and the current value of a set		processing depends on the PL_PTB_SIZE and the current value of a set
	of variables:		of variables:
	PL_PTB_SIZE < MIN_PLPMTU		PL_PTB_SIZE < MIN_PLPMTU
	* Invalid PL_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
	(i.e., PLPMTU is not modified).		(i.e., PLPMTU is not modified).
	* The information could be utilized as an input that triggers		* The information could be utilized as an input that triggers
	skipping to change at page 20, line 15 ¶		skipping to change at page 20, line 26 ¶
	BASE_PLPMTU <= PL_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_PLPMTU (the PLPMTU is reduced to the BASE_PLPMTU		be set to BASE_PLPMTU (the PLPMTU is reduced to the BASE_PLPMTU
	to 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 PL_PTB_SIZE reported in the PTB message can be		PLPMTU. The PL_PTB_SIZE reported in the PTB message can be
	used to initialize a search algorithm.		used to initialize a search algorithm.
	PL_PTB_SIZE = PLPMTU
	* Completes the search for a larger PLPMTU.
	PLPMTU < PL_PTB_SIZE < PROBED_SIZE		PLPMTU < PL_PTB_SIZE < PROBED_SIZE
	* The PLPMTU continues to be valid, but the size of a packet used		* The PLPMTU continues to be valid, but the size of a packet used
	to search (PROBED_SIZE) 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 PL_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.
	PL_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
	(i.e., PLPMTU is 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.
	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 only be performed at one layer between a pair of
	already used in a lower layer DPLPMTUD SHOULD only be performed once		endpoints. Therefore, an upper PL or application should avoid using
	between a pair of endpoints. A PL MUST adjust the MPS indicated by		DPLPMTUD when this is already enabled in a lower layer. A PL MUST
	DPLPMTUD to account for any additional overhead introduced by the PL.		adjust the MPS indicated by DPLPMTUD to account for any additional
			overhead introduced by the PL.
	+----------------------+		+----------------------+
	| Application* |		| Application* |
	+-----+------------+---+		+-----+------------+---+
	| |		| |
	+---+--+ +--+--+		+---+--+ +--+--+
	| QUIC*| |SCTP*|		| QUIC*| |SCTP*|
	+---+--+ +-+-+-+		+---+--+ +-+-+-+
	| | |		| | |
	+---+ +----+ |		+---+ +----+ |
	skipping to change at page 21, line 47 ¶		skipping to change at page 22, line 4 ¶
	DPLPMTUD.		DPLPMTUD.
	5.1.1. Timers		5.1.1. Timers
	The method utilizes up to three timers:		The method utilizes up to three timers:
	PROBE_TIMER: The PROBE_TIMER is configured to expire after a period		PROBE_TIMER: The PROBE_TIMER is configured to expire after a period
	longer than the maximum time to receive an acknowledgment to a		longer than the maximum time to receive an acknowledgment to a
	probe packet. This value MUST NOT be smaller than 1 second, and		probe packet. This value MUST NOT be smaller than 1 second, and
	SHOULD be larger than 15 seconds. Guidance on selection of the		SHOULD be larger than 15 seconds. Guidance on selection of the
	timer value are provided in section 3.1.1 of the UDP Usage		timer value are provided in Section 3.1.1 of the UDP Usage
	Guidelines [RFC8085].		Guidelines [BCP145].
	PMTU_RAISE_TIMER: The PMTU_RAISE_TIMER is configured to the period a		PMTU_RAISE_TIMER: The PMTU_RAISE_TIMER is configured to the period a
	sender will continue to use the current PLPMTU, after which it re-		sender will continue to use the current PLPMTU, after which it re-
	enters the Search phase. This timer has a period of 600 seconds,		enters the Search phase. This timer has a period of 600 seconds,
	as recommended by PLPMTUD [RFC4821].		as recommended by PLPMTUD [RFC4821].
	DPLPMTUD MAY inhibit sending probe packets when no application		DPLPMTUD MAY inhibit sending probe packets when no application
	data has been sent since the previous probe packet. A PL		data has been sent since the previous probe packet. A PL
	preferring to use an up-to-date PMTU once user data is sent again,		preferring to use an up-to-date PMTU once user data is sent again,
	can choose to continue PMTU discovery for each path. However,		can choose to continue PMTU discovery for each path. However,
	this could result in sending additional packets.		this will result in sending additional packets.
	CONFIRMATION_TIMER: When an acknowledged PL is used, this timer MUST		CONFIRMATION_TIMER: When an acknowledged PL is used, this timer MUST
	NOT be used. For other PLs, the CONFIRMATION_TIMER is configured		NOT be used. For other PLs, the CONFIRMATION_TIMER is configured
	to the period a PL sender waits before confirming the current		to the period a PL sender waits before confirming the current
	PLPMTU is still supported. This is less than the PMTU_RAISE_TIMER		PLPMTU is still supported. This is less than the PMTU_RAISE_TIMER
	and used to decrease the PLPMTU (e.g., when a black hole is		and used to decrease the PLPMTU (e.g., when a black hole is
	encountered). Confirmation needs to be frequent enough when data		encountered). Confirmation needs to be frequent enough when data
	is flowing that the sending PL does not black hole extensive		is flowing that the sending PL does not black hole extensive
	amounts of traffic. Guidance on selection of the timer value are		amounts of traffic. Guidance on selection of the timer value are
	provided in section 3.1.1 of the UDP Usage Guidelines [RFC8085].		provided in Section 3.1.1 of the UDP Usage Guidelines [BCP145].
	DPLPMTUD MAY inhibit sending probe packets when no application		DPLPMTUD MAY inhibit sending probe packets when no application
	data has been sent since the previous probe packet. A PL		data has been sent since the previous probe packet. A PL
	preferring to use an up-to-date PMTU once user data is sent again,		preferring to use an up-to-date PMTU once user data is sent again,
	can choose to continue PMTU discovery for each path. However,		can choose to continue PMTU discovery for each path. However,
	this could result in sending additional packets.		this could result in sending additional packets.
	The various timers could be implemented using a single timer		DPLPMTD specifies various timers, however an implementation could
			choose to realise these timer functions using a single 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 value greater 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_PLPMTU: The MIN_PLPMTU is the smallest allowed probe packet		MIN_PLPMTU: The MIN_PLPMTU is the smallest size of PLPMTU that
	size. For IPv6, this value is 1280 bytes, as specified in		DPLPMTUD will attempt to use. For IPv6, this size is greater than
	[RFC8200]. For IPv4, the minimum value is 68 bytes.		or equal to the size at the PL that results in an 1280 byte IPv6
			packet, as specified in [RFC8200]. For IPv4, this size is greater
	Note: An IPv4 router is required to be able to forward a datagram		than or equal to the size at the PL that results in an 68 byte
	of 68 bytes without further fragmentation. This is the combined		IPv4 packet. Note: An IPv4 router is required to be able to
	size of an IPv4 header and the minimum fragment size of 8 bytes.		forward a datagram of 68 bytes without further fragmentation.
	In addition, receivers are required to be able to reassemble		This is the combined size of an IPv4 header and the minimum
	fragmented datagrams at least up to 576 bytes, as stated in		fragment size of 8 bytes. In addition, receivers are required to
	section 3.3.3 of [RFC1122].		be able to reassemble fragmented datagrams at least up to 576
			bytes, as stated in section 3.3.3 of [RFC1122].
	MAX_PLPMTU: The MAX_PLPMTU is the largest size of PLPMTU. This has		MAX_PLPMTU: The MAX_PLPMTU is the largest size of PLPMTU. This has
	to be less than or equal to the maximum size of the PL packet that		to be less than or equal to the maximum size of the PL packet that
	can be sent on the outgoing interface (constrained by the local		can be sent on the outgoing interface (constrained by the local
	interface MTU). When known, this also ought to be less than the		interface MTU). When known, this also ought to be less than the
	maximum size of PL packet that can be received by the remote		maximum size of PL packet that can be received by the remote
	endpoint (constrained by EMTU_R). It can be limited by the design		endpoint (constrained by EMTU_R). It can be limited by the design
	or configuration of the PL being used. An application, or PL, MAY		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		choose a smaller MAX_PLPMTU when there is no need to send packets
	larger than a specific size.		larger than a specific size.
	BASE_PLPMTU: The BASE_PLPMTU is a configured size expected to work		BASE_PLPMTU: The BASE_PLPMTU is a configured size expected to work
	for most paths. The size is equal to or larger than the		for most paths. The size is equal to or larger than the
	MIN_PLPMTU and smaller than the MAX_PLPMTU. In the case of IPv6,		MIN_PLPMTU and smaller than the MAX_PLPMTU. For most PLs a
	this value is derived from the IPv6 minimum link MTU of 1280 bytes		suitable BASE_PLPMTU will be larger than 1200 bytes. When using
	[RFC8200]. When using IPv4, there is no currently equivalent size		IPv4, there is no currently equivalent size specified and a
	specified and a default BASE_PLPMTU of 1200 bytes is RECOMMENDED.		default BASE_PLPMTU of 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
	packet. This is a tentative value for the PLPMTU, which is		as determined at the PL. This is a tentative value for the
	awaiting confirmation by an acknowledgment.		PLPMTU, which is 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
	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.
	skipping to change at page 24, line 41 ¶		skipping to change at page 24, line 50 ¶
	| 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_PLPMTU. This phase is implicit for a		packets of the BASE_PLPMTU. The confirmation of connectivity is
	connection-oriented PL (where it can be performed in a PL		implicit for a connection-oriented PL (where it can be performed
	connection handshake). A connectionless PL sends a probe packet		in a PL connection handshake). A connectionless PL sends a probe
	and uses acknowledgment of this probe packet to confirm that the		packet and uses acknowledgment of this probe packet to confirm
	remote peer is reachable.		that the remote peer is reachable.
	The sender also confirms that BASE_PLPMTU is supported across the		The sender also confirms that BASE_PLPMTU is supported across the
	network path. This may be achieved using a PL mechanism (e.g.,		network path. This may be achieved using a PL mechanism (e.g.,
	using a handshake packet of size BASE_PLPMTU), or by sending a		using a handshake packet of size BASE_PLPMTU), or by sending a
	probe packet of size BASE_PLPMTU and confirming that this is		probe packet of size BASE_PLPMTU and confirming that this is
	received.		received.
	A probe packet of size BASE_PLPMTU can be sent immediately on the		A probe packet of size BASE_PLPMTU can be sent immediately on the
	initial entry to the Base Phase (following a connectivity check).		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
	skipping to change at page 27, line 13 ¶		skipping to change at page 27, 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: PLPTB_SIZE < BASE_PLPMTU | |		| connectivity PTB: PL_PTB_SIZE < BASE_PLPMTU | |
	+--------------------+ +---------------+ |		+--------------------+ +---------------+ |
	| | |		| | |
	v | BASE_PLPMTU 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_PLPMTU 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: PLPTB_SIZE = PLPMTU +----+		+----+ PTB: PL_PTB_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 < PLPTB_SIZE < PROBED_SIZE		PLPMTU < PL_PTB_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. When transitioning to		indicates connectivity to the remote PL. When transitioning to
	the BASE state, a probe packet of size BASE_PLPMTU can be sent		the BASE state, a probe packet of size BASE_PLPMTU can be sent
	skipping to change at page 29, line 50 ¶		skipping to change at page 29, line 50 ¶
	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_PLPMTU. MAX_PLPMTU is the minimum of the local		than or equal to MAX_PLPMTU. MAX_PLPMTU is the minimum of the local
	MTU and EMTU_R (when this is learned from the remote endpoint). The		MTU and EMTU_R (when this is learned from the remote endpoint). The
	MAX_PLPMTU MAY be reduced by an application that sets a maximum to		MAX_PLPMTU MAY be reduced by an application that sets a maximum to
	the size of 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. Each probe packet
	trigger the sending of probe packets of size PROBED_SIZE, larger than		successfully sent to the remote peer is confirmed by acknowledgment
	the PLPMTU. Each probe packet successfully sent to the remote peer		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 31, line 42 ¶		skipping to change at page 31, line 40 ¶
	6.1. Application support for DPLPMTUD with UDP or UDP-Lite		6.1. Application support for DPLPMTUD with UDP or UDP-Lite
	The current specifications of UDP [RFC0768] and UDP-Lite [RFC3828] do		The current specifications of UDP [RFC0768] and UDP-Lite [RFC3828] do
	not define a method in the RFC-series that supports PLPMTUD. In		not define a method in the RFC-series that supports PLPMTUD. In
	particular, the UDP transport does not provide the transport features		particular, the UDP transport does not provide the transport features
	needed to implement datagram PLPMTUD.		needed to implement datagram PLPMTUD.
	The DPLPMTUD method can be implemented as a part of an application		The DPLPMTUD method can be implemented as a part of an application
	built directly or indirectly on UDP or UDP-Lite, but relies on		built directly or indirectly on UDP or UDP-Lite, but relies on
	higher-layer protocol features to implement the method [RFC8085].		higher-layer protocol features to implement the method [BCP145].
	Some primitives used by DPLPMTUD might not be available via the		Some primitives used by DPLPMTUD might not be available via the
	Datagram API (e.g., the ability to access the PLPMTU from the IP		Datagram API (e.g., the ability to access the PLPMTU from the IP
	layer cache, or interpret received PTB messages).		layer cache, or interpret received PTB messages).
	In addition, it is recommended that PMTU discovery is not performed		In addition, it is recommended that PMTU discovery is not performed
	by multiple protocol layers. An application SHOULD avoid using		by multiple protocol layers. An application SHOULD avoid using
	DPLPMTUD when the underlying transport system provides this		DPLPMTUD when the underlying transport system provides this
	capability. To use common method for managing the PLPMTU has		capability. A common method for managing the PLPMTU has benefits,
	benefits, both in the ability to share state between different		both in the ability to share state between different processes and
	processes and opportunities to coordinate probing.		opportunities to coordinate probing for different PL instances.
	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 acknowledgment 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		from off-path insertion of data [BCP145]. Suitable methods include a
	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.
	skipping to change at page 33, line 8 ¶		skipping to change at page 32, line 48 ¶
	6.1.5. Validating the Path		6.1.5. Validating the Path
	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 [BCP145].
	This requires that the application checks each received PTB message		This requires that the application checks each received PTB message
	to validate that it was is received in response to transmitted		to validate that it was is received in response to transmitted
	traffic and that the reported PL_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] recommended an endpoint
	endpoint apply the techniques in RFC4821 on a per-destination-address		apply the techniques in RFC4821 on a per-destination-address basis.
	basis. The specification for DPLPMTUD continues the practice of		The specification for DPLPMTUD continues the practice of using the PL
	using the PL to discover the PMTU, but updates, RFC4960 with a		to discover the PMTU, but updates, RFC4960 with a recommendation to
	recommendation to use the method specified in this document: The		use the method specified in this document: The RECOMMENDED method for
	RECOMMENDED method for generating probes is to add a chunk consisting		generating probes is to add a chunk consisting only of padding to an
	only of padding to an SCTP message. The PAD chunk defined in		SCTP message. The PAD chunk defined in [RFC4820] SHOULD be attached
	[RFC4820] SHOULD be attached to a minimum length HEARTBEAT (HB) chunk		to a minimum length HEARTBEAT (HB) chunk to build a probe packet.
	to build a probe packet. This enables probing without affecting the		This enables probing without affecting the transfer of user messages
	transfer of user messages and without being limited by congestion		and without being limited by congestion control or flow control.
	control or flow control. This is preferred to using DATA chunks		This is preferred to using DATA chunks (with padding as required) as
	(with padding as required) as path probes.		path probes.
	Section 6.9 of [RFC4960] describes dividing the user messages into		Section 6.9 of [RFC4960] describes dividing the user messages into
	data chunks sent by the PL when using SCTP. This notes that once an		data chunks sent by the PL when using SCTP. This notes that once an
	SCTP message has been sent, it cannot be re-segmented. [RFC4960]		SCTP message has been sent, it cannot be re-segmented. [RFC4960]
	describes the method to retransmit data chunks when the MPS has		describes the method to retransmit data chunks when the MPS has
	reduced, and the use of IP fragmentation for this case.		reduced, and the use of IP fragmentation for this case. This is
			unchanged by this document.
	6.2.1. SCTP/IPv4 and SCTP/IPv6		6.2.1. SCTP/IPv4 and SCTP/IPv6
	6.2.1.1. Initial Connectivity		6.2.1.1. Initial Connectivity
	The base protocol is specified in [RFC4960]. This provides an		The base protocol is specified in [RFC4960]. This provides an
	acknowledged PL. A sender can therefore enter the BASE state as soon		acknowledged PL. A sender can therefore enter the BASE state as soon
	as connectivity has been confirmed.		as connectivity has been confirmed.
	6.2.1.2. Sending SCTP Probe Packets		6.2.1.2. Sending SCTP Probe Packets
	Probe packets consist of an SCTP common header followed by a		Probe packets consist of an SCTP common header followed by a
	HEARTBEAT chunk and a PAD chunk. The PAD chunk is used to control		HEARTBEAT chunk and a PAD chunk. The PAD chunk is used to control
	the length of the probe packet. The HEARTBEAT chunk is used to		the length of the probe packet. The HEARTBEAT chunk is used to
	trigger the sending of a HEARTBEAT ACK chunk. The reception of the		trigger the sending of a HEARTBEAT ACK chunk. The reception of the
	HEARTBEAT ACK chunk acknowledges reception of a successful probe. A		HEARTBEAT ACK chunk acknowledges reception of a successful probe. A
	successful probe updates the association and path counters, but an		successful probe updates the association and path counters, but an
	unsuccessful probe is discounted (assumed to be a result of choosing		unsuccessful probe is discounted (assumed to be a result of choosing
	too large a PLPMTU).		too large a PLPMTU).
	The HEARTBEAT chunk carries a Heartbeat Information parameter which		The SCTP sender needs to be able to determine the total size of a
	includes, besides the information suggested in [RFC4960], the probe		probe packet. The HEARTBEAT chunk could carry a Heartbeat
	size, which is the size of the complete datagram. The size of the		Information parameter that includes, besides the information
	PAD chunk is therefore computed by reducing the probing size by the		suggested in [RFC4960], the probe size to help an implementation
	IPv4 or IPv6 header size, the SCTP common header, the HEARTBEAT		associate a HEARTBEAT-ACK with the size of probe that was sent. The
	request and the PAD chunk header. The payload of the PAD chunk		sender could also use other methods, such as sending a nonce and
	contains arbitrary data.		verifying the information returned also contains the corresponding
			nonce. The length of the PAD chunk is computed by reducing the
			probing size by the size of the SCTP common header and the HEARTBEAT
			chunk. The payload of the PAD chunk contains arbitrary data. When
			transmitted at the IP layer, the PMTU size also includes the IPv4 or
			IPv6 header(s).
	Probing starts directly after the PL handshake, before data is sent.		Probing can start directly after the PL handshake, this can be done
	Assuming this behavior (i.e., the PMTU is smaller than or equal to		before data is sent. Assuming this behavior (i.e., the PMTU is
	the interface MTU), this process will take several round trip time		smaller than or equal to the interface MTU), this process will take
	periods, dependent on the number of DPLPMTUD probes sent. The		several round trip time periods, dependent on the number of DPLPMTUD
	Heartbeat timer can be used to implement the PROBE_TIMER.		probes sent. The 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
	skipping to change at page 34, line 45 ¶		skipping to change at page 34, line 44 ¶
	from the PTB_SIZE reported in the PTB message SHOULD be used with the		from the PTB_SIZE reported in the PTB message SHOULD be used with the
	DPLPMTUD algorithm, providing that the reported PL_PTB_SIZE is less		DPLPMTUD algorithm, providing that the reported PL_PTB_SIZE is less
	than the current probe size (see 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 at the end of section 5.6: "The
	section 5.6: "The RECOMMENDED method for determining the MTU of the		RECOMMENDED method for determining the MTU of the path is specified
	path is specified in XXXTHISRFCXXX".		in XXXTHISRFCXXX".
	XXX RFC EDITOR - please replace XXXTHISRFCXXX when published XXX		XXX RFC EDITOR - please replace XXXTHISRFCXXX when published XXX
	6.2.2.1. Initial Connectivity		6.2.2.1. 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.
	6.2.2.2. Sending SCTP/UDP Probe Packets		6.2.2.2. Sending SCTP/UDP Probe Packets
	Packet probing can be performed as specified in Section 6.2.1.2. The		Packet probing can be performed as specified in Section 6.2.1.2. The
	maximum payload is reduced by 8 bytes, which has to be considered		size of the probe packet includes the 8 bytes of UDP Header. This
	when filling the PAD chunk.		has to be considered when filling the probe packet with the PAD
			chunk.
	6.2.2.3. Validating the Path with SCTP/UDP		6.2.2.3. Validating the Path with SCTP/UDP
	Since SCTP provides an acknowledged PL, a sender MUST NOT implement		SCTP provides an acknowledged PL, therefore a sender does not
	the CONFIRMATION_TIMER while in the SEARCH_COMPLETE state.		implement 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 PL_PTB_SIZE calculated from the PTB_SIZE		validation is completed, the PL_PTB_SIZE calculated from the PTB_SIZE
	in the PTB message SHOULD be used with the DPLPMTUD providing that		in the PTB message SHOULD be used with the DPLPMTUD providing that
	skipping to change at page 35, line 48 ¶		skipping to change at page 36, line 7 ¶
	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.
	6.2.3.2. Sending SCTP/DTLS Probe Packets		6.2.3.2. Sending SCTP/DTLS Probe Packets
	Packet probing can be done, as specified in Section 6.2.1.2.		Packet probing can be done, as specified in Section 6.2.1.2. The
			maximum payload is reduced by the size of the DTLS headers, which has
			to be considered when filling the PAD chunk. The size of the probe
			packet includes the DTLS PL headers. This has to be considered when
			filling the probe packet with the PAD chunk.
	6.2.3.3. Validating the Path with SCTP/DTLS		6.2.3.3. Validating the Path with SCTP/DTLS
	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.
	6.2.3.4. Handling of PTB Messages by SCTP/DTLS		6.2.3.4. Handling of PTB Messages by SCTP/DTLS
	[RFC4960] does not specify a way to validate SCTP/DTLS ICMP message		[RFC4960] does not specify a way to validate SCTP/DTLS ICMP message
	payload. This can prevent processing of PTB messages at the PL.		payload and neither does this document. This can prevent processing
			of PTB messages at the PL.
	6.3. DPLPMTUD for QUIC		6.3. DPLPMTUD for QUIC
	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
	skipping to change at page 36, line 45 ¶		skipping to change at page 37, line 5 ¶
	ceases to send QUIC packets on the affected path. This could result		ceases to send QUIC packets on the affected path. This could result
	in termination of the connection if an alternative path cannot be		in termination of the connection if an alternative path cannot be
	found [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.
			QUIC provides an acknowledged PL, a sender can therefore enter the
			BASE 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		Probe packets consist of a QUIC Header and a payload containing a
	PADDING Frames and a PING Frame. PADDING Frames are a single octet		PING Frame and multiple PADDING Frames. A PADDING Frame is
	(0x00) and several of these can be used to create a probe packet of		represented by a single octet (0x00). Several PADDING Frames are
	size PROBED_SIZE. QUIC provides an acknowledged PL, a sender can		used together to control the length of the probe packet. The PING
	therefore enter the BASE state as soon as connectivity has been		Frame is used to trigger generation of an acknowledgement.
	confirmed.
	The current specification of QUIC sets the following:		The current specification of QUIC sets the following:
	* BASE_PLPMTU: A QUIC sender pads initial packets to confirm the		* BASE_PLPMTU: A QUIC sender pads initial packets to confirm the
	path can support packets of the required size, which sets the		path can support packets of the required size, which sets the
	BASE_PLPMTU and MIN_PLPMTU.		BASE_PLPMTU and MIN_PLPMTU.
	* MIN_PLPMTU: A QUIC sender that determines the MIN_PLPMTU has		* MIN_PLPMTU: A QUIC sender that determines the MIN_PLPMTU has
	fallen MUST immediately stop sending on the affected path.		fallen MUST immediately stop sending on the 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, therefore a sender does 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 identifiers (CIDs) in the		information (e.g., validation of connection identifiers (CIDs) in the
	quoted packet of any received ICMP message).		quoted packet of any received ICMP message).
	7. Acknowledgments		7. Acknowledgments
	skipping to change at page 38, line 10 ¶		skipping to change at page 38, line 19 ¶
	To avoid excessive load, the interval between individual probe		To avoid excessive load, the interval between individual probe
	packets MUST be at least one RTT, and the interval between rounds of		packets MUST be at least one RTT, and the interval between rounds of
	probing is determined by the PMTU_RAISE_TIMER.		probing is determined by the PMTU_RAISE_TIMER.
	A PL sender needs to ensure that the method used to confirm reception		A PL sender needs to ensure that the method used to confirm reception
	of probe packets protects from off-path attackers injecting packets		of probe packets protects from off-path attackers injecting packets
	into the path. This protection is provided in IETF-defined protocols		into the path. This protection is provided in IETF-defined protocols
	(e.g., TCP, SCTP) using a randomly-initialized sequence number. A		(e.g., TCP, SCTP) using a randomly-initialized sequence number. A
	description of one way to do this when using UDP is provided in		description of one way to do this when using UDP is provided in
	section 5.1 of [RFC8085]).		section 5.1 of [BCP145]).
	There are cases where ICMP Packet Too Big (PTB) messages are not		There are cases where ICMP Packet Too Big (PTB) messages are not
	delivered due to policy, configuration or equipment design (see		delivered due to policy, configuration or equipment design (see
	Section 1.1). This method therefore does not rely upon PTB messages		Section 1.1). This method therefore does not rely upon PTB messages
	being received, but is able to utilize these when they are received		being received, but is able to utilize these when they are received
	by the sender. PTB messages could potentially be used to cause a		by the sender. PTB messages could potentially be used to cause a
	node to inappropriately reduce the PLPMTU. A node supporting		node to inappropriately reduce the PLPMTU. A node supporting
	DPLPMTUD MUST therefore appropriately validate the payload of PTB		DPLPMTUD MUST therefore appropriately validate the payload of PTB
	messages to ensure these are received in response to transmitted		messages to ensure these are received in response to transmitted
	traffic (i.e., a reported error condition that corresponds to a		traffic (i.e., a reported error condition that corresponds to a
	datagram actually sent by the path layer, see Section 4.6.1).		datagram actually sent by the path layer, see Section 4.6.1).
	An on-path attacker able to create a PTB message could forge PTB		An on-path attacker able to create a PTB message could forge PTB
	messages that include a valid quoted IP packet. Such an attack could		messages that include a valid quoted IP packet. Such an attack could
	be used to drive down the PLPMTU. There are two ways this method can		be used to drive down the PLPMTU. An on-path device could similarly
	be mitigated against such attacks: First, by ensuring that a PL		force a reduction of the PLPMTU by implementing a policy that drops
	sender never reduces the PLPMTU below the base size, solely in		packets larger than a configured size. There are two ways this
			method can be mitigated against such attacks: First, by ensuring that
			a PL sender never reduces the PLPMTU below the base size, solely in
	response to receiving a PTB message. This is achieved by first		response to receiving a PTB message. This is achieved by first
	entering the BASE state when such a message is received. Second, the		entering the BASE state when such a message is received. Second, the
	design does not require processing of PTB messages, a PL sender could		design does not require processing of PTB messages, a PL sender could
	therefore suspend processing of PTB messages (e.g., in a robustness		therefore suspend processing of PTB messages (e.g., in a robustness
	mode after detecting that subsequent probes actually confirm that a		mode after detecting that subsequent probes actually confirm that a
	size larger than the PTB_SIZE is supported by a path).		size larger than the PTB_SIZE is supported by a path).
	Parsing the quoted packet inside a PTB message can introduce addional		Parsing the quoted packet inside a PTB message can introduce addional
	per-packet processing at the PL sender. This processing SHOULD be		per-packet processing at the PL sender. This processing SHOULD be
	limited to avoid a denial of service attack when arbitrary headers		limited to avoid a denial of service attack when arbitrary headers
	skipping to change at page 39, line 7 ¶		skipping to change at page 39, line 18 ¶
	hole data by indicating a size larger than supported by the path.		hole data by indicating a size larger than supported by the path.
	It is possible that the information about a path is not stable. This		It is possible that the information about a path is not stable. This
	could be a result of forwarding across more than one path that has a		could be a result of forwarding across more than one path that has a
	different actual PMTU or a single path presents a varying PMTU. The		different actual PMTU or a single path presents a varying PMTU. The
	design of a PLPMTUD implementation SHOULD consider how to mitigate		design of a PLPMTUD implementation SHOULD consider how to mitigate
	the effects of varying path information. One possible mitigation is		the effects of varying path information. One possible mitigation is
	to provide robustness (see Section 5.4) in the method that avoids		to provide robustness (see Section 5.4) in the method that avoids
	oscillation in the MPS.		oscillation in the MPS.
	A node performing DPLPMTUD could experience conflicting information
	about the size of supported probe packets. This could occur when
	multiple paths are concurrently in use and these exhibit a different
	PMTU. If not considered, this could result in packets not being
	delivered (black holed) when the PLPMTU results in a packet 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 the design ought to avoid adding anything		integrity mechanisms, then the design ought to avoid adding anything
	(e.g., padding) to DPLPMTUD probe packets that is not also protected		(e.g., padding) to DPLPMTUD probe packets that is not also protected
	by those cryptographic mechanisms.		by those cryptographic mechanisms.
	10. References		10. References
	10.1. Normative References		10.1. Normative References
			[BCP145] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage
			Guidelines", BCP 145, RFC 8085, March 2017.
			<https://www.rfc-editor.org/info/bcp145>
	[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-
	transport-27.txt>.		transport-27.txt>.
	[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,		[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
	DOI 10.17487/RFC0768, August 1980,		DOI 10.17487/RFC0768, August 1980,
	<https://www.rfc-editor.org/info/rfc768>.		<https://www.rfc-editor.org/info/rfc768>.
	skipping to change at page 40, line 27 ¶		skipping to change at page 40, line 36 ¶
	[RFC4960] Stewart, R., Ed., "Stream Control Transmission Protocol",		[RFC4960] Stewart, R., Ed., "Stream Control Transmission Protocol",
	RFC 4960, DOI 10.17487/RFC4960, September 2007,		RFC 4960, DOI 10.17487/RFC4960, September 2007,
	<https://www.rfc-editor.org/info/rfc4960>.		<https://www.rfc-editor.org/info/rfc4960>.
	[RFC6951] Tuexen, M. and R. Stewart, "UDP Encapsulation of Stream		[RFC6951] Tuexen, M. and R. Stewart, "UDP Encapsulation of Stream
	Control Transmission Protocol (SCTP) Packets for End-Host		Control Transmission Protocol (SCTP) Packets for End-Host
	to End-Host Communication", RFC 6951,		to End-Host Communication", RFC 6951,
	DOI 10.17487/RFC6951, May 2013,		DOI 10.17487/RFC6951, May 2013,
	<https://www.rfc-editor.org/info/rfc6951>.		<https://www.rfc-editor.org/info/rfc6951>.
	[RFC8085] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage
	Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085,
	March 2017, <https://www.rfc-editor.org/info/rfc8085>.
	[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC		[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
	2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,		2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
	May 2017, <https://www.rfc-editor.org/info/rfc8174>.		May 2017, <https://www.rfc-editor.org/info/rfc8174>.
	[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6		[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
	(IPv6) Specification", STD 86, RFC 8200,		(IPv6) Specification", STD 86, RFC 8200,
	DOI 10.17487/RFC8200, July 2017,		DOI 10.17487/RFC8200, July 2017,
	<https://www.rfc-editor.org/info/rfc8200>.		<https://www.rfc-editor.org/info/rfc8200>.
	[RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed.,		[RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed.,
	skipping to change at page 46, line 34 ¶		skipping to change at page 46, line 40 ¶
	* Updated text and address nits from OPSDIR, ART and IESG reviews.		* Updated text and address nits from OPSDIR, ART and IESG reviews.
	* Order PTB processing based on PL_PTB_SIZE		* Order PTB processing based on PL_PTB_SIZE
	Working group draft -19:		Working group draft -19:
	* Updated text and address nits based on comments from Tim Chown and		* Updated text and address nits based on comments from Tim Chown and
	Murray S. Kucherawy.		Murray S. Kucherawy.
			Working group draft -20:
			* Address nits and comments from IESG
			* Refer to BCP 145 rather than RFC 8085 in most places.
			* Update probing method text for SCTP and QUIC.
	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
End of changes. 80 change blocks.
	252 lines changed or deleted		284 lines changed or added
This html diff was produced by rfcdiff 1.47. The latest version is available from http://tools.ietf.org/tools/rfcdiff/