draft-ietf-tsvwg-datagram-plpmtud-16.txt		draft-ietf-tsvwg-datagram-plpmtud-17.txt
	Internet Engineering Task Force G. Fairhurst		Internet Engineering Task Force G. Fairhurst
	Internet-Draft T. Jones		Internet-Draft T. Jones
	Updates: 4821, 4960, 6951, 8085, 8261 (if University of Aberdeen		Updates: 4821, 4960, 6951, 8085, 8261 (if University of Aberdeen
	approved) M. Tuexen		approved) M. Tuexen
	Intended status: Standards Track I. Ruengeler		Intended status: Standards Track I. Ruengeler
	Expires: 10 September 2020 T. Voelker		Expires: 24 September 2020 T. Voelker
	Muenster University of Applied Sciences		Muenster University of Applied Sciences
	9 March 2020		23 March 2020
	Packetization Layer Path MTU Discovery for Datagram Transports		Packetization Layer Path MTU Discovery for Datagram Transports
	draft-ietf-tsvwg-datagram-plpmtud-16		draft-ietf-tsvwg-datagram-plpmtud-17
	Abstract		Abstract
	This document describes a robust method for Path MTU Discovery		This document describes a robust method for Path MTU Discovery
	(PMTUD) for datagram Packetization Layers (PLs). It describes an		(PMTUD) for datagram Packetization Layers (PLs). It describes an
	extension to RFC 1191 and RFC 8201, which specifies ICMP-based Path		extension to RFC 1191 and RFC 8201, which specifies ICMP-based Path
	MTU Discovery for IPv4 and IPv6. The method allows a PL, or a		MTU Discovery for IPv4 and IPv6. The method allows a PL, or a
	datagram application that uses a PL, to discover whether a network		datagram application that uses a PL, to discover whether a network
	path can support the current size of datagram. This can be used to		path can support the current size of datagram. This can be used to
	detect and reduce the message size when a sender encounters a packet		detect and reduce the message size when a sender encounters a packet
	skipping to change at page 2, line 15 ¶		skipping to change at page 2, line 15 ¶
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at https://datatracker.ietf.org/drafts/current/.		Drafts is at https://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		material or to cite them other than as "work in progress."
	This Internet-Draft will expire on 10 September 2020.		This Internet-Draft will expire on 24 September 2020.
	Copyright Notice		Copyright Notice
	Copyright (c) 2020 IETF Trust and the persons identified as the		Copyright (c) 2020 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	This document is subject to BCP 78 and the IETF Trust's Legal		This document is subject to BCP 78 and the IETF Trust's Legal
	Provisions Relating to IETF Documents (https://trustee.ietf.org/		Provisions Relating to IETF Documents (https://trustee.ietf.org/
	license-info) in effect on the date of publication of this document.		license-info) in effect on the date of publication of this document.
	Please review these documents carefully, as they describe your rights		Please review these documents carefully, as they describe your rights
	skipping to change at page 2, line 48 ¶		skipping to change at page 2, line 48 ¶
	3. Features Required to Provide Datagram PLPMTUD . . . . . . . . 10		3. Features Required to Provide Datagram PLPMTUD . . . . . . . . 10
	4. DPLPMTUD Mechanisms . . . . . . . . . . . . . . . . . . . . . 13		4. DPLPMTUD Mechanisms . . . . . . . . . . . . . . . . . . . . . 13
	4.1. PLPMTU Probe Packets . . . . . . . . . . . . . . . . . . 13		4.1. PLPMTU Probe Packets . . . . . . . . . . . . . . . . . . 13
	4.2. Confirmation of Probed Packet Size . . . . . . . . . . . 14		4.2. Confirmation of Probed Packet Size . . . . . . . . . . . 14
	4.3. Black Hole Detection . . . . . . . . . . . . . . . . . . 15		4.3. Black Hole Detection . . . . . . . . . . . . . . . . . . 15
	4.4. The Maximum Packet Size (MPS) . . . . . . . . . . . . . . 16		4.4. The Maximum Packet Size (MPS) . . . . . . . . . . . . . . 16
	4.5. Disabling the Effect of PMTUD . . . . . . . . . . . . . . 17		4.5. Disabling the Effect of PMTUD . . . . . . . . . . . . . . 17
	4.6. Response to PTB Messages . . . . . . . . . . . . . . . . 17		4.6. Response to PTB Messages . . . . . . . . . . . . . . . . 17
	4.6.1. Validation of PTB Messages . . . . . . . . . . . . . 17		4.6.1. Validation of PTB Messages . . . . . . . . . . . . . 17
	4.6.2. Use of PTB Messages . . . . . . . . . . . . . . . . . 18		4.6.2. Use of PTB Messages . . . . . . . . . . . . . . . . . 18
	5. Datagram Packetization Layer PMTUD . . . . . . . . . . . . . 19		5. Datagram Packetization Layer PMTUD . . . . . . . . . . . . . 20
	5.1. DPLPMTUD Components . . . . . . . . . . . . . . . . . . . 20		5.1. DPLPMTUD Components . . . . . . . . . . . . . . . . . . . 20
	5.1.1. Timers . . . . . . . . . . . . . . . . . . . . . . . 20		5.1.1. Timers . . . . . . . . . . . . . . . . . . . . . . . 21
	5.1.2. Constants . . . . . . . . . . . . . . . . . . . . . . 21		5.1.2. Constants . . . . . . . . . . . . . . . . . . . . . . 21
	5.1.3. Variables . . . . . . . . . . . . . . . . . . . . . . 22		5.1.3. Variables . . . . . . . . . . . . . . . . . . . . . . 22
	5.1.4. Overview of DPLPMTUD Phases . . . . . . . . . . . . . 23		5.1.4. Overview of DPLPMTUD Phases . . . . . . . . . . . . . 23
	5.2. State Machine . . . . . . . . . . . . . . . . . . . . . . 24		5.2. State Machine . . . . . . . . . . . . . . . . . . . . . . 25
	5.3. Search to Increase the PLPMTU . . . . . . . . . . . . . . 27		5.3. Search to Increase the PLPMTU . . . . . . . . . . . . . . 28
	5.3.1. Probing for a larger PLPMTU . . . . . . . . . . . . . 27		5.3.1. Probing for a larger PLPMTU . . . . . . . . . . . . . 28
	5.3.2. Selection of Probe Sizes . . . . . . . . . . . . . . 28		5.3.2. Selection of Probe Sizes . . . . . . . . . . . . . . 29
	5.3.3. Resilience to Inconsistent Path Information . . . . . 28		5.3.3. Resilience to Inconsistent Path Information . . . . . 29
	5.4. Robustness to Inconsistent Paths . . . . . . . . . . . . 29		5.4. Robustness to Inconsistent Paths . . . . . . . . . . . . 30
	6. Specification of Protocol-Specific Methods . . . . . . . . . 29		6. Specification of Protocol-Specific Methods . . . . . . . . . 30
	6.1. Application support for DPLPMTUD with UDP or UDP-Lite . . 29		6.1. Application support for DPLPMTUD with UDP or UDP-Lite . . 30
	6.1.1. Application Request . . . . . . . . . . . . . . . . . 30		6.1.1. Application Request . . . . . . . . . . . . . . . . . 31
	6.1.2. Application Response . . . . . . . . . . . . . . . . 30		6.1.2. Application Response . . . . . . . . . . . . . . . . 31
	6.1.3. Sending Application Probe Packets . . . . . . . . . . 30		6.1.3. Sending Application Probe Packets . . . . . . . . . . 31
	6.1.4. Initial Connectivity . . . . . . . . . . . . . . . . 30		6.1.4. Initial Connectivity . . . . . . . . . . . . . . . . 31
	6.1.5. Validating the Path . . . . . . . . . . . . . . . . . 30		6.1.5. Validating the Path . . . . . . . . . . . . . . . . . 31
	6.1.6. Handling of PTB Messages . . . . . . . . . . . . . . 30		6.1.6. Handling of PTB Messages . . . . . . . . . . . . . . 31
	6.2. DPLPMTUD for SCTP . . . . . . . . . . . . . . . . . . . . 31		6.2. DPLPMTUD for SCTP . . . . . . . . . . . . . . . . . . . . 32
	6.2.1. SCTP/IPv4 and SCTP/IPv6 . . . . . . . . . . . . . . . 31		6.2.1. SCTP/IPv4 and SCTP/IPv6 . . . . . . . . . . . . . . . 32
	6.2.1.1. Initial Connectivity . . . . . . . . . . . . . . 31		6.2.1.1. Initial Connectivity . . . . . . . . . . . . . . 32
	6.2.1.2. Sending SCTP Probe Packets . . . . . . . . . . . 31		6.2.1.2. Sending SCTP Probe Packets . . . . . . . . . . . 32
	6.2.1.3. Validating the Path with SCTP . . . . . . . . . . 32		6.2.1.3. Validating the Path with SCTP . . . . . . . . . . 33
	6.2.1.4. PTB Message Handling by SCTP . . . . . . . . . . 32		6.2.1.4. PTB Message Handling by SCTP . . . . . . . . . . 33
	6.2.2. DPLPMTUD for SCTP/UDP . . . . . . . . . . . . . . . . 32		6.2.2. DPLPMTUD for SCTP/UDP . . . . . . . . . . . . . . . . 33
	6.2.2.1. Initial Connectivity . . . . . . . . . . . . . . 32		6.2.2.1. Initial Connectivity . . . . . . . . . . . . . . 33
	6.2.2.2. Sending SCTP/UDP Probe Packets . . . . . . . . . 33		6.2.2.2. Sending SCTP/UDP Probe Packets . . . . . . . . . 34
	6.2.2.3. Validating the Path with SCTP/UDP . . . . . . . . 33		6.2.2.3. Validating the Path with SCTP/UDP . . . . . . . . 34
	6.2.2.4. Handling of PTB Messages by SCTP/UDP . . . . . . 33		6.2.2.4. Handling of PTB Messages by SCTP/UDP . . . . . . 34
	6.2.3. DPLPMTUD for SCTP/DTLS . . . . . . . . . . . . . . . 33		6.2.3. DPLPMTUD for SCTP/DTLS . . . . . . . . . . . . . . . 34
	6.2.3.1. Initial Connectivity . . . . . . . . . . . . . . 33		6.2.3.1. Initial Connectivity . . . . . . . . . . . . . . 34
	6.2.3.2. Sending SCTP/DTLS Probe Packets . . . . . . . . . 33		6.2.3.2. Sending SCTP/DTLS Probe Packets . . . . . . . . . 34
	6.2.3.3. Validating the Path with SCTP/DTLS . . . . . . . 33		6.2.3.3. Validating the Path with SCTP/DTLS . . . . . . . 34
	6.2.3.4. Handling of PTB Messages by SCTP/DTLS . . . . . . 34		6.2.3.4. Handling of PTB Messages by SCTP/DTLS . . . . . . 35
	6.3. DPLPMTUD for QUIC . . . . . . . . . . . . . . . . . . . . 34		6.3. DPLPMTUD for QUIC . . . . . . . . . . . . . . . . . . . . 35
	6.3.1. Initial Connectivity . . . . . . . . . . . . . . . . 34		6.3.1. Initial Connectivity . . . . . . . . . . . . . . . . 35
	6.3.2. Sending QUIC Probe Packets . . . . . . . . . . . . . 34		6.3.2. Sending QUIC Probe Packets . . . . . . . . . . . . . 35
	6.3.3. Validating the Path with QUIC . . . . . . . . . . . . 35		6.3.3. Validating the Path with QUIC . . . . . . . . . . . . 36
	6.3.4. Handling of PTB Messages by QUIC . . . . . . . . . . 35		6.3.4. Handling of PTB Messages by QUIC . . . . . . . . . . 36
	7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 35		7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 36
	8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 35		8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 36
	9. Security Considerations . . . . . . . . . . . . . . . . . . . 35		9. Security Considerations . . . . . . . . . . . . . . . . . . . 36
	10. References . . . . . . . . . . . . . . . . . . . . . . . . . 37		10. References . . . . . . . . . . . . . . . . . . . . . . . . . 38
	10.1. Normative References . . . . . . . . . . . . . . . . . . 37		10.1. Normative References . . . . . . . . . . . . . . . . . . 38
	10.2. Informative References . . . . . . . . . . . . . . . . . 38		10.2. Informative References . . . . . . . . . . . . . . . . . 39
	Appendix A. Revision Notes . . . . . . . . . . . . . . . . . . . 39		Appendix A. Revision Notes . . . . . . . . . . . . . . . . . . . 40
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 43		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 45
	1. Introduction		1. Introduction
	The IETF has specified datagram transport using UDP, SCTP, and DCCP,		The IETF has specified datagram transport using UDP, SCTP, and DCCP,
	as well as protocols layered on top of these transports (e.g., SCTP/		as well as protocols layered on top of these transports (e.g., SCTP/
	UDP, DCCP/UDP, QUIC/UDP), and direct datagram transport over the IP		UDP, DCCP/UDP, QUIC/UDP), and direct datagram transport over the IP
	network layer. This document describes a robust method for Path MTU		network layer. This document describes a robust method for Path MTU
	Discovery (PMTUD) that can be used with these transport protocols (or		Discovery (PMTUD) that can be used with these transport protocols (or
	the applications that use their transport service) to discover an		the applications that use their transport service) to discover an
	appropriate size of packet to use across an Internet path.		appropriate size of packet to use across an Internet path.
	skipping to change at page 5, line 36 ¶		skipping to change at page 5, line 36 ¶
	receive a packet because of its size. This could be due to		receive a packet because of its size. This could be due to
	misconfiguration of the layer 2 path between nodes, for instance		misconfiguration of the layer 2 path between nodes, for instance
	the MTU configured in a layer 2 switch, or misconfiguration of the		the MTU configured in a layer 2 switch, or misconfiguration of the
	Maximum Receive Unit (MRU). If a packet is dropped by the link,		Maximum Receive Unit (MRU). If a packet is dropped by the link,
	this will not cause a PTB message to be sent to the original		this will not cause a PTB message to be sent to the original
	sender.		sender.
	Another failure could result if a node that is not on the network		Another failure could result if a node that is not on the network
	path sends a PTB message that attempts to force a sender to change		path sends a PTB message that attempts to force a sender to change
	the effective PMTU [RFC8201]. A sender can protect itself from		the effective PMTU [RFC8201]. A sender can protect itself from
	reacting to such messages by utilising the quoted packet within a PTB		reacting to such messages by utilizing the quoted packet within a PTB
	message payload to validate that the received PTB message was		message payload to validate that the received PTB message was
	generated in response to a packet that had actually originated from		generated in response to a packet that had actually originated from
	the sender. However, there are situations where a sender would be		the sender. However, there are situations where a sender would be
	unable to provide this validation. Examples where validation of the		unable to provide this validation. Examples where validation of the
	PTB message is not possible include:		PTB message is not possible include:
	* When a router issuing the ICMP message implements RFC792		* When a router issuing the ICMP message implements RFC792
	[RFC0792], it is only required to include the first 64 bits of the		[RFC0792], it is only required to include the first 64 bits of the
	IP payload of the packet within the quoted payload. There could		IP payload of the packet within the quoted payload. There could
	be insufficient bytes remaining for the sender to interpret the		be insufficient bytes remaining for the sender to interpret the
	skipping to change at page 6, line 24 ¶		skipping to change at page 6, line 24 ¶
	validate the message, because validation depends on information		validate the message, because validation depends on information
	about the active transport flows at an endpoint node (e.g., the		about the active transport flows at an endpoint node (e.g., the
	socket/address pairs being used, and other protocol header		socket/address pairs being used, and other protocol header
	information).		information).
	* When a packet is encapsulated/tunneled over an encrypted		* When a packet is encapsulated/tunneled over an encrypted
	transport, the tunnel/encapsulation ingress might have		transport, the tunnel/encapsulation ingress might have
	insufficient context, or computational power, to reconstruct the		insufficient context, or computational power, to reconstruct the
	transport header that would be needed to perform validation.		transport header that would be needed to perform validation.
	* A Network Addres Translation (NAT) device that translates a packet		* A Network Address Translation (NAT) device that translates a
	header, ought to also translate ICMP messages and update the ICMP		packet header, ought to also translate ICMP messages and update
	quoted packet [RFC5508] in that message. If this is not correctly		the ICMP quoted packet [RFC5508] in that message. If this is not
	translated then the sender would not be able to associate the		correctly translated then the sender would not be able to
	message with the PL that originated the packet, and hence this		associate the message with the PL that originated the packet, and
	ICMP message cannot be validated.		hence this ICMP message cannot be validated.
	1.2. Packetization Layer Path MTU Discovery		1.2. Packetization Layer Path MTU Discovery
	The term Packetization Layer (PL) has been introduced to describe the		The term Packetization Layer (PL) has been introduced to describe the
	layer that is responsible for placing data blocks into the payload of		layer that is responsible for placing data blocks into the payload of
	IP packets and selecting an appropriate MPS. This function is often		IP packets and selecting an appropriate MPS. This function is often
	performed by a transport protocol (e.g., DCCP, RTP, SCTP, QUIC), but		performed by a transport protocol (e.g., DCCP, RTP, SCTP, QUIC), but
	can also be performed by other encapsulation methods working above		can also be performed by other encapsulation methods working above
	the transport layer.		the transport layer.
	skipping to change at page 7, line 36 ¶		skipping to change at page 7, line 36 ¶
	the lower layers, although it can utilize PTB messages when these		the lower layers, although it can utilize PTB messages when these
	received messages are made available to the PL.		received messages are made available to the PL.
	The message size guidelines in section 3.2 of the UDP Usage		The message size guidelines in section 3.2 of the UDP Usage
	Guidelines [RFC8085] state "an application SHOULD either use the Path		Guidelines [RFC8085] state "an application SHOULD either use the Path
	MTU information provided by the IP layer or implement Path MTU		MTU information provided by the IP layer or implement Path MTU
	Discovery (PMTUD)", but does not provide a mechanism for discovering		Discovery (PMTUD)", but does not provide a mechanism for discovering
	the largest size of unfragmented datagram that can be used on a		the largest size of unfragmented datagram that can be used on a
	network path. The present document updates RFC 8085 to specify this		network path. The present document updates RFC 8085 to specify this
	method in place of PLPMTUD [RFC4821] and provides a mechanism for		method in place of PLPMTUD [RFC4821] and provides a mechanism for
	sharing the discovered largest size as the Maximum Packet Size (MPS)		sharing the discovered largest size as the MPS (see Section 4.4).
	(see Section 4.4).
	Section 10.2 of [RFC4821] recommended a PLPMTUD probing method for		Section 10.2 of [RFC4821] recommended a PLPMTUD probing method for
	the Stream Control Transport Protocol (SCTP). SCTP utilizes probe		the Stream Control Transport Protocol (SCTP). SCTP utilizes probe
	packets consisting of a minimal sized HEARTBEAT chunk bundled with a		packets consisting of a minimal sized HEARTBEAT chunk bundled with a
	PAD chunk as defined in [RFC4820]. However, RFC 4821 did not provide		PAD chunk as defined in [RFC4820]. However, RFC 4821 did not provide
	a complete specification. The present document replaces this by		a complete specification. The present document replaces this by
	providing a complete specification.		providing a complete specification.
	The Datagram Congestion Control Protocol (DCCP) [RFC4340] requires		The Datagram Congestion Control Protocol (DCCP) [RFC4340] requires
	implementations to support Classical PMTUD and states that a DCCP		implementations to support Classical PMTUD and states that a DCCP
	skipping to change at page 8, line 22 ¶		skipping to change at page 8, line 22 ¶
	[RFC8261].		[RFC8261].
	2. Terminology		2. Terminology
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",		The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and		"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
	"OPTIONAL" in this document are to be interpreted as described in BCP		"OPTIONAL" in this document are to be interpreted as described in BCP
	14 [RFC2119] [RFC8174] when, and only when, they appear in all		14 [RFC2119] [RFC8174] when, and only when, they appear in all
	capitals, as shown here.		capitals, as shown here.
	Other terminology is directly copied from [RFC4821], and the		The following terminology is defined. Relevant terms are directly
	definitions in [RFC1122].		copied from [RFC4821], and the definitions in [RFC1122].
			Acknowledged PL: A PL that includes a mechanism that can confirm
			successful delivery of datagrams to the remote PL endpoint (e.g.,
			SCTP). Typically, the PL receiver returns acknowledgments
			corresponding to the received datagrams, which can be utilised to
			detect black-holing of packets (c.f., Unacknowledged PL).
	Actual PMTU: The Actual PMTU is the PMTU of a network path between a		Actual PMTU: The Actual PMTU is the PMTU of a network path between a
	sender PL and a destination PL, which the DPLPMTUD algorithm seeks		sender PL and a destination PL, which the DPLPMTUD algorithm seeks
	to determine.		to determine.
	Black Hole: A Black Hole is encountered when a sender is unaware		Black Hole: A Black Hole is encountered when a sender is unaware
	that packets are not being delivered to the destination end point.		that packets are not being delivered to the destination end point.
	Two types of Black Hole are relevant to DPLPMTUD:		Two types of Black Hole are relevant to DPLPMTUD:
	* Packets encounter a packet Black Hole when packets are not		* Packets encounter a packet Black Hole when packets are not
	skipping to change at page 9, line 7 ¶		skipping to change at page 9, line 12 ¶
	Classical Path MTU Discovery: Classical PMTUD is a process described		Classical Path MTU Discovery: Classical PMTUD is a process described
	in [RFC1191] and [RFC8201], in which nodes rely on PTB messages to		in [RFC1191] and [RFC8201], in which nodes rely on PTB messages to
	learn the largest size of unfragmented packet that can be used		learn the largest size of unfragmented packet that can be used
	across a network path.		across a network path.
	Datagram: A datagram is a transport-layer protocol data unit,		Datagram: A datagram is a transport-layer protocol data unit,
	transmitted in the payload of an IP packet.		transmitted in the payload of an IP packet.
	Effective PMTU: The Effective PMTU is the current estimated value		Effective PMTU: The Effective PMTU is the current estimated value
	for PMTU that is used by a PMTUD. This is equivalent to the		for PMTU that is used by a PMTUD. This is equivalent to the
	PLPMTU derived by PLPMTUD.		PLPMTU derived by PLPMTUD plus the size of any headers added below
			the PL, including the IP layer headers.
	EMTU_S: The Effective MTU for sending (EMTU_S) is defined in		EMTU_S: The Effective MTU for sending (EMTU_S) is defined in
	[RFC1122] as "the maximum IP datagram size that may be sent, for a		[RFC1122] as "the maximum IP datagram size that may be sent, for a
	particular combination of IP source and destination addresses...".		particular combination of IP source and destination addresses...".
	EMTU_R: The Effective MTU for receiving (EMTU_R) is designated in		EMTU_R: The Effective MTU for receiving (EMTU_R) is designated in
	[RFC1122] as the largest datagram size that can be reassembled by		[RFC1122] as the largest datagram size that can be reassembled by
	EMTU_R (Effective MTU to receive).		EMTU_R (Effective MTU to receive).
	Link: A Link is a communication facility or medium over which nodes		Link: A Link is a communication facility or medium over which nodes
	skipping to change at page 9, line 35 ¶		skipping to change at page 9, line 41 ¶
	could more properly be called the IP MTU, to be consistent with		could more properly be called the IP MTU, to be consistent with
	how other standards organizations use the acronym. This includes		how other standards organizations use the acronym. This includes
	the IP header, but excludes link layer headers and other framing		the IP header, but excludes link layer headers and other framing
	that is not part of IP or the IP payload. Other standards		that is not part of IP or the IP payload. Other standards
	organizations generally define the link MTU to include the link		organizations generally define the link MTU to include the link
	layer headers. This specification continues the requirement in		layer headers. This specification continues the requirement in
	[RFC4821], that states "All links MUST enforce their MTU: links		[RFC4821], that states "All links MUST enforce their MTU: links
	that might non- deterministically deliver packets that are larger		that might non- deterministically deliver packets that are larger
	than their rated MTU MUST consistently discard such packets."		than their rated MTU MUST consistently discard such packets."
	MAX_PMTU: The MAX_PMTU is the largest size of PLPMTU that DPLPMTUD		MAX_PLPMTU: The MAX_PLPMTU is the largest size of PLPMTU that
	will attempt to use.		DPLPMTUD will attempt to use.
	MPS: The Maximum Packet Size (MPS) is the largest size of		MIN_PLPMTU: The MIN_PLPMTU is the smallest size of PLPMTU that
	application data block that can be sent across a network path by a		DPLPMTUD will attempt to use.
	PL. In DPLPMTUD this quantity is derived from the PLPMTU by
	taking into consideration the size of the lower protocol layer
	headers. Probe packets generated by DPLPMTUD can have a size
	larger than the MPS.
	MIN_PMTU: The MIN_PMTU is the smallest size of PLPMTU that DPLPMTUD		MPS: MPS: The Maximum Packet Size (MPS) is the largest size of
	will attempt to use.		application data block that can be sent across a network path by a
			PL using a single Datagram.
	Packet: A Packet is the IP header plus the IP payload.		Packet: A Packet is the IP header plus the IP payload.
	Packetization Layer (PL): The Packetization Layer (PL) is a layer of		Packetization Layer (PL): The PL is a layer of the network stack
	the network stack that places data into packets and performs		that places data into packets and performs transport protocol
	transport protocol functions. Examples of a PL include: TCP,		functions. Examples of a PL include: TCP, SCTP, SCTP over DTLS or
	SCTP, SCTP over DTLS or QUIC.		QUIC.
	Path: The Path is the set of links and routers traversed by a packet		Path: The Path is the set of links and routers traversed by a packet
	between a source node and a destination node by a particular flow.		between a source node and a destination node by a particular flow.
	Path MTU (PMTU): The Path MTU (PMTU) is the minimum of the Link MTU		Path MTU (PMTU): The Path MTU (PMTU) is the minimum of the Link MTU
	of all the links forming a network path between a source node and		of all the links forming a network path between a source node and
	a destination node.		a destination node, as used by PMTUD.
	PTB_SIZE: The PTB_SIZE is a value reported in a validated PTB		PTB_SIZE: The PTB_SIZE is a value reported in a validated PTB
	message that indicates next hop link MTU of a router along the		message that indicates next hop link MTU of a router along the
	path.		path.
	PLPMTU: The Packetization Layer PMTU is an estimate of the actual		PL_PTB_SIZE: The size reported in a validated PTB message, reduced
	PMTU provided by the DPLPMTUD algorithm.		by the size of all headers added by layers below the PL.
			PLPMTU: The Packetization Layer PMTU is an estimate of the largest
			size of PL datagram that can be sent by a path, controled by
			PLPMTUD.
	PLPMTUD: Packetization Layer Path MTU Discovery (PLPMTUD), the		PLPMTUD: Packetization Layer Path MTU Discovery (PLPMTUD), the
	method described in this document for datagram PLs, which is an		method described in this document for datagram PLs, which is an
	extension to Classical PMTU Discovery.		extension to Classical PMTU Discovery.
	Probe packet: A probe packet is a datagram sent with a purposely		Probe packet: A probe packet is a datagram sent with a purposely
	chosen size (typically the current PLPMTU or larger) to detect if		chosen size (typically the current PLPMTU or larger) to detect if
	packets of this size can be successfully sent end-to-end across		packets of this size can be successfully sent end-to-end across
	the network path.		the network path.
			Unacknowledged PL: A PL that does not itself provide a mechanism to
			confirm delivery of datagrams to the remote PL endpoint (e.g.,
			UDP), and therefore requires DPLPMTUD to provide a mechanism to
			detect black-holing of packets (c.f., Acknowledged PL).
	3. Features Required to Provide Datagram PLPMTUD		3. Features Required to Provide Datagram PLPMTUD
	The principles expressed in [RFC4821] apply to the use of the		The principles expressed in [RFC4821] apply to the use of the
	technique with any PL. TCP PLPMTUD has been defined using standard		technique with any PL. TCP PLPMTUD has been defined using standard
	TCP protocol mechanisms. Unlike TCP, datagram PLs require additional		TCP protocol mechanisms. Unlike TCP, a datagram PL requires
	mechanisms and considerations to implement PLPMTUD.		additional mechanisms and considerations to implement PLPMTUD.
	The requirements for datagram PLPMTUD are:		The requirements for datagram PLPMTUD are:
	1. PLPMTU: The PLPMTU (specified as the effective PMTU in Section 1		1. Managing the PLPMTU: For datagram PLs, the PLPMTU is managed by
	of [RFC1191]) is equivalent to the EMTU_S (specified in		DPLPMTUD. A PL MUST NOT send a datagram (other than a probe
	[RFC1122]). For datagram PLs,] the PLPMTU is managed by		packet) with a size at the PL layer that is larger than the
	DPLPMTUD. A PL MUST NOT send a packet (other than a probe		current PLPMTU.
	packet) with a size larger than the current PLPMTU at the
	network layer.
	2. Probe packets: On request, a DPLPMTUD sender is REQUIRED to be		2. Probe packets: On request, a DPLPMTUD sender is REQUIRED to be
	able to transmit a packet larger than the PLMPMTU. This is used		able to transmit a packet larger than the PLMPMTU. This is used
	to send a probe packet. In IPv4, a probe packet MUST be sent		to send a probe packet. In IPv4, a probe packet MUST be sent
	with the Don't Fragment (DF) bit set in the IP header, and		with the Don't Fragment (DF) bit set in the IP header, and
	without network layer endpoint fragmentation. In IPv6, a probe		without network layer endpoint fragmentation. In IPv6, a probe
	packet is always sent without source fragmentation (as specified		packet is always sent without source fragmentation (as specified
	in section 5.4 of [RFC8201]).		in section 5.4 of [RFC8201]).
	3. Reception feedback: The destination PL endpoint is REQUIRED to		3. Reception feedback: The destination PL endpoint is REQUIRED to
	skipping to change at page 11, line 21 ¶		skipping to change at page 11, line 29 ¶
	4. Probe loss recovery: It is RECOMMENDED to use probe packets that		4. Probe loss recovery: It is RECOMMENDED to use probe packets that
	do not carry any user data that would require retransmission if		do not carry any user data that would require retransmission if
	lost. Most datagram transports permit this. If a probe packet		lost. Most datagram transports permit this. If a probe packet
	contains user data requiring retransmission in case of loss, the		contains user data requiring retransmission in case of loss, the
	PL (or layers above) are REQUIRED to arrange any retransmission/		PL (or layers above) are REQUIRED to arrange any retransmission/
	repair of any resulting loss. The PL is REQUIRED to be robust		repair of any resulting loss. The PL is REQUIRED to be robust
	in the case where probe packets are lost due to other reasons		in the case where probe packets are lost due to other reasons
	(including link transmission error, congestion).		(including link transmission error, congestion).
	5. PMTU parameters: A DPLPMTUD sender is RECOMMENDED to utilise		5. PMTU parameters: A DPLPMTUD sender is RECOMMENDED to utilize
	information about the maximum size of packet that can be		information about the maximum size of packet that can be
	transmitted by the sender on the local link (e.g., the local		transmitted by the sender on the local link (e.g., the local
	Link MTU). It MAY utilize similar information about the		Link MTU). It MAY utilize similar information about the maximum
	receiver when this is supplied (note this could be less than		size a receiver can accept when this is supplied (note this
	EMTU_R). This avoids implementations trying to send probe		could be less than EMTU_R). This avoids implementations trying
	packets that can not be transmitted by the local link. Too high		to send probe packets that can not be transferred by the local
	of a value could reduce the efficiency of the search algorithm.		link. Too high of a value could reduce the efficiency of the
	Some applications also have a maximum transport protocol data		search algorithm. Some applications also have a maximum
	unit (PDU) size, in which case there is no benefit from probing		transport protocol data unit (PDU) size, in which case there is
	for a size larger than this (unless a transport allows		no benefit from probing for a size larger than this (unless a
	multiplexing multiple applications PDUs into the same datagram).		transport allows multiplexing multiple applications PDUs into
			the same datagram).
	6. Processing PTB messages: A DPLPMTUD sender MAY optionally		6. Processing PTB messages: A DPLPMTUD sender MAY optionally
	utilize PTB messages received from the network layer to help		utilize PTB messages received from the network layer to help
	identify when a network path does not support the current size		identify when a network path does not support the current size
	of probe packet. Any received PTB message MUST be validated		of probe packet. Any received PTB message MUST be validated
	before it is used to update the PLPMTU discovery information		before it is used to update the PLPMTU discovery information
	[RFC8201]. This validation confirms that the PTB message was		[RFC8201]. This validation confirms that the PTB message was
	sent in response to a packet originating by the sender, and		sent in response to a packet originating by the sender, and
	needs to be performed before the PLPMTU discovery method reacts		needs to be performed before the PLPMTU discovery method reacts
	to the PTB message. A PTB message MUST NOT be used to increase		to the PTB message. A PTB message MUST NOT be used to increase
	the PLPMTU [RFC8201], but could trigger a probe to test for a		the PLPMTU [RFC8201], but could trigger a probe to test for a
	larger PLPMTU. A PTB_SIZE greater than the currently probed		larger PLPMTU. A PL_PTB_SIZE that is greater than that
	MUST be ignored.		currently probed MUST be ignored. A valid PTB_SIZE is converted
			to a PL_PTB_SIZE before it is to be used in the DPLPMTUD state
			machine.
	7. Probing and congestion control: The decision about when to send		7. Probing and congestion control: The decision about when to send
	a probe packet does not need to be limited by the congestion		a probe packet does not need to be limited by the congestion
	controller. When not controlled by the congestion controller,		controller. When not controlled by the congestion controller,
	the interval between probe packets MUST be at least one RTT. If		the interval between probe packets MUST be at least one RTT. If
	transmission of probe packets is limited by the congestion		transmission of probe packets is limited by the congestion
	controller, this could result in transmission of probe packets		controller, this could result in transmission of probe packets
	being delayed.		being delayed or suspended during congestion.
	8. Loss of a probe packet SHOULD NOT be treated as an indication of		8. Loss of a probe packet SHOULD NOT be treated as an indication of
	congestion and SHOULD NOT trigger a congestion control reaction		congestion and SHOULD NOT trigger a congestion control reaction
	[RFC4821], because this could result in unnecessary reduction of		[RFC4821], because this could result in unnecessary reduction of
	the sending rate.		the sending rate.
	9. An update to the PLPMTU (or MPS) MUST NOT modify the congestion		9. An update to the PLPMTU (or MPS) MUST NOT modify the congestion
	window measured in bytes [RFC4821]. Therefore, an increase in		window measured in bytes [RFC4821]. Therefore, an increase in
	the packet size does not cause an increase the data rate in		the packet size does not cause an increase the data rate in
	bytes per second.		bytes per second.
	10. Probing and flow control: Flow control at the PL concerns the		10. Probing and flow control: Flow control at the PL concerns the
	end-to-end flow of data using the PL service. This does not		end-to-end flow of data using the PL service. This does not
	apply to DPLPMTU when probe packets use a design that does not		apply to DPLPMTU when probe packets use a design that does not
	carry user data to the remote application.		carry user data to the remote application.
	11. Shared PLPMTU state: The PLPMTU value MAY also be stored with		11. Shared PLPMTU state: The PMTU value calculated from the PLPMTU
	the corresponding entry associated with the destination in the		MAY also be stored with the corresponding entry associated with
	IP layer cache, and used by other PL instances. The		the destination in the IP layer cache, and used by other PL
	specification of PLPMTUD [RFC4821] states: "If PLPMTUD updates		instances. The specification of PLPMTUD [RFC4821] states: "If
	the MTU for a particular path, all Packetization Layer sessions		PLPMTUD updates the MTU for a particular path, all Packetization
	that share the path representation (as described in Section 5.2		Layer sessions that share the path representation (as described
	of [RFC4821]) SHOULD be notified to make use of the new MTU".		in Section 5.2 of [RFC4821]) SHOULD be notified to make use of
	Such methods MUST be robust to the wide variety of underlying		the new MTU". Such methods MUST be robust to the wide variety
	network forwarding behaviors. Section 5.2 of [RFC8201] provides		of underlying network forwarding behaviors. Section 5.2 of
	guidance on the caching of PMTU information and also the		[RFC8201] provides guidance on the caching of PMTU information
	relation to IPv6 flow labels.		and also the relation to IPv6 flow labels.
	In addition, the following principles are stated for design of a		In addition, the following principles are stated for design of a
	DPLPMTUD method:		DPLPMTUD method:
	* Maximum Packet Size (MPS): A PL MAY be designed to segment data		* A PL MAY be designed to segment data blocks larger than the MPS
	blocks larger than the MPS into multiple datagrams. However, not		into multiple datagrams. However, not all datagram PLs support
	all datagram PLs support segmentation of data blocks. It is		segmentation of data blocks. It is RECOMMENDED that methods avoid
	RECOMMENDED that methods avoid forcing an application to use an		forcing an application to use an arbitrary small MPS for
	arbitrary small MPS for transmission while the method is searching		transmission while the method is searching for the currently
	for the currently supported PLPMTU. A reduced MPS can adversely		supported PLPMTU. A reduced MPS can adversely impact the
	impact the performance of an application.		performance of an application.
	* To assist applications in choosing a suitable data block size, the		* To assist applications in choosing a suitable data block size, the
	PL is RECOMMENDED to provide a primitive that returns the MPS		PL is RECOMMENDED to provide a primitive that returns the MPS
	derived from the PLPMTU to the higher layer using the PL. The		derived from the PLPMTU to the higher layer using the PL. The
	value of the MPS can change following a change in the path, or		value of the MPS can change following a change in the path, or
	loss of probe packets.		loss of probe packets.
	* Path validation: It is RECOMMENDED that methods are robust to path		* Path validation: It is RECOMMENDED that methods are robust to path
	changes that could have occurred since the path characteristics		changes that could have occurred since the path characteristics
	were last confirmed, and to the possibility of inconsistent path		were last confirmed, and to the possibility of inconsistent path
	skipping to change at page 14, line 33 ¶		skipping to change at page 14, line 43 ¶
	block in a datagram without the padding data). This retransmited		block in a datagram without the padding data). This retransmited
	data block might possibly need to be sent using a smaller PLPMTU,		data block might possibly need to be sent using a smaller PLPMTU,
	which could need the PL to to use a smaller packet size to traverse		which could need the PL to to use a smaller packet size to traverse
	the end-to-end path. (This could utilize endpoint network-layer or a		the end-to-end path. (This could utilize endpoint network-layer or a
	PL that can re-segment the data block into multiple datagrams).		PL that can re-segment the data block into multiple datagrams).
	DPLPMTUD MAY choose to use only one of these methods to simplify the		DPLPMTUD MAY choose to use only one of these methods to simplify the
	implementation.		implementation.
	Probe messages sent by a PL MUST contain enough information to		Probe messages sent by a PL MUST contain enough information to
	uniquely identify the probe within Maximum Segment Lifetime, while		uniquely identify the probe within Maximum Segment Lifetime (e.g.,
	being robust to reordering and replay of probe response and PTB		including a unique identifier from the PL or the DPLPMTUD
	messages.		implementation), while being robust to reordering and replay of probe
			response and PTB messages.
	4.2. Confirmation of Probed Packet Size		4.2. Confirmation of Probed Packet Size
	The PL needs a method to determine (confirm) when probe packets have		The PL needs a method to determine (confirm) when probe packets have
	been successfully received end-to-end across a network path.		been successfully received end-to-end across a network path.
	Transport protocols can include end-to-end methods that detect and		Transport protocols can include end-to-end methods that detect and
	report reception of specific datagrams that they send (e.g., DCCP and		report reception of specific datagrams that they send (e.g., DCCP and
	SCTP provide keep-alive/heartbeat features). When supported, this		SCTP provide keep-alive/heartbeat features). When supported, this
	mechanism MAY also be used by DPLPMTUD to acknowledge reception of a		mechanism MAY also be used by DPLPMTUD to acknowledge reception of a
	skipping to change at page 15, line 15 ¶		skipping to change at page 15, line 26 ¶
	Section 6 specifies this function for a set of IETF-specified		Section 6 specifies this function for a set of IETF-specified
	protocols.		protocols.
	4.3. Black Hole Detection		4.3. Black Hole Detection
	Black Hole Detection is triggered by an indication that the network		Black Hole Detection is triggered by an indication that the network
	path could be unable to support the current PLPMTU size.		path could be unable to support the current PLPMTU size.
	There are three ways to detect black holes:		There are three ways to detect black holes:
	* A validated PTB message can be received that indicates a PTB_SIZE		* A validated PTB message can be received that indicates a
	less than the current PLPMTU. A DPLPMTUD method MUST NOT rely		PL_PTB_SIZE less than the current PLPMTU. A DPLPMTUD method MUST
	soley on this method.		NOT rely solely on this method.
	* A PL can use the DPLPMTUD probing mechanism to periodically		* A PL can use the DPLPMTUD probing mechanism to periodically
	generate probe packets of the size of the current PLPMTU (e.g.,		generate probe packets of the size of the current PLPMTU (e.g.,
	using the confirmation timer Section 5.1.1). A timer tracks		using the confirmation timer Section 5.1.1). A timer tracks
	whether acknowledgments are received. Successive loss of probes		whether acknowledgments are received. Successive loss of probes
	is an indication that the current path no longer supports the		is an indication that the current path no longer supports the
	PLPMTU (e.g., when the number of probe packets sent without		PLPMTU (e.g., when the number of probe packets sent without
	receiving an acknowledgement, PROBE_COUNT, becomes greater than		receiving an acknowledgment, PROBE_COUNT, becomes greater than
	MAX_PROBES).		MAX_PROBES).
	* A PL can utilise an event that indicates the network path no		* A PL can utilize an event that indicates the network path no
	longer sustains the sender's PLPMTU size. This could use a		longer sustains the sender's PLPMTU size. This could use a
	mechanism implemented within the PL to detect excessive loss of		mechanism implemented within the PL to detect excessive loss of
	data sent with a specific packet size and then conclude that this		data sent with a specific packet size and then conclude that this
	excessive loss could be a result of an invalid PLPMTU (as in		excessive loss could be a result of an invalid PLPMTU (as in
	PLPMTUD for TCP [RFC4821]).		PLPMTUD for TCP [RFC4821]).
	A PL MAY inhibit sending probe packets when no application data has		A PL MAY inhibit sending probe packets when no application data has
	been sent since the previous probe packet. A PL preferring to use an		been sent since the previous probe packet. A PL preferring to use an
	up-to-data PLPMTU once user data is sent again, MAY choose to		up-to-data PLPMTU once user data is sent again, MAY choose to
	continue PLPMTU discovery for each path. However, this could result		continue PLPMTU discovery for each path. However, this could result
	skipping to change at page 16, line 11 ¶		skipping to change at page 16, line 17 ¶
	the new PLPMTU can be successfully used across the path. A probe		the new PLPMTU can be successfully used across the path. A probe
	packet could need to have a size less than the size of the data block		packet could need to have a size less than the size of the data block
	generated by the application.		generated by the application.
	4.4. The Maximum Packet Size (MPS)		4.4. The Maximum Packet Size (MPS)
	The result of probing determines a usable PLPMTU, which is used to		The result of probing determines a usable PLPMTU, which is used to
	set the MPS used by the application. The MPS is smaller than the		set the MPS used by the application. The MPS is smaller than the
	PLPMTU because it is reduced by the size of PL headers (including the		PLPMTU because it is reduced by the size of PL headers (including the
	overhead of security-related fields such as an AEAD tag and TLS		overhead of security-related fields such as an AEAD tag and TLS
	record layer padding) and any IP options or extensions added to the		record layer padding). The relationship between the MPS and the
	PL packet. The relationship between the MPS and the PLPMTUD is		PLPMTUD is illustrated in Figure 1.
	illustrated in Figure 1.
	any additional		any additional
	headers .--- MPS -----.		headers .--- MPS -----.
	| | |		| | |
	v v v		v v v
	+------------------------------+		+------------------------------+
	| IP | ** | PL | protocol data |		| IP | ** | PL | protocol data |
	+------------------------------+		+------------------------------+
	<---------- PLPMTU ------------>		<----- PLPMTU ----->
			<---------- PMTU -------------->
	Figure 1: Relationship between MPS and PLPMTU		Figure 1: Relationship between MPS and PLPMTU
	A PL is unable to send a packet (other than a probe packet) with a		A PL is unable to send a packet (other than a probe packet) with a
	size larger than the current PLPMTU at the network layer. To avoid		size larger than the current PLPMTU at the network layer. To avoid
	this, a PL MAY be designed to segment data blocks larger than the MPS		this, a PL MAY be designed to segment data blocks larger than the MPS
	into multiple datagrams.		into multiple datagrams.
	DPLPMTUD seeks to avoid IP fragmentation. An attempt to send a data		DPLPMTUD seeks to avoid IP fragmentation. An attempt to send a data
	block larger than the MPS will therefore fail if a PL is unable to		block larger than the MPS will therefore fail if a PL is unable to
	segment data. To determine the largest data block that can be sent,		segment data. To determine the largest data block that can be sent,
	a PL SHOULD provide applications with a primitive that returns the		a PL SHOULD provide applications with a primitive that returns the
	Maximum Packet Size (MPS), derived from the current PLPMTU.		MPS, derived from the current PLPMTU.
	If DPLPMTUD results in a change to the MPS, the application needs to		If DPLPMTUD results in a change to the MPS, the application needs to
	adapt to the new MPS. A particular case can arise when packets have		adapt to the new MPS. A particular case can arise when packets have
	been sent with a size less than the MPS and the PLPMTU was		been sent with a size less than the MPS and the PLPMTU was
	subsequently reduced. If these packets are lost, the PL MAY segment		subsequently reduced. If these packets are lost, the PL MAY segment
	the data using the new MPS. If a PL is unable to re-segment a		the data using the new MPS. If a PL is unable to re-segment a
	previously sent datagram (e.g., [RFC4960]), then the sender either		previously sent datagram (e.g., [RFC4960]), then the sender either
	discards the datagram or could perform retransmission using network-		discards the datagram or could perform retransmission using network-
	layer fragmentation to form multiple IP packets not larger than the		layer fragmentation to form multiple IP packets not larger than the
	PLPMTU. For IPv4, the use of endpoint fragmentation by the sender is		PLPMTU. For IPv4, the use of endpoint fragmentation by the sender is
	preferred over clearing the DF-bit in the IPv4 header. Operational		preferred over clearing the DF-bit in the IPv4 header. Operational
	experience reveals that IP fragmentation can reduce the reliability		experience reveals that IP fragmentation can reduce the reliability
	of Internet communication [I-D.ietf-intarea-frag-fragile], which may		of Internet communication [I-D.ietf-intarea-frag-fragile], which may
	reduce the success of retransmission.		reduce the success of retransmission.
	4.5. Disabling the Effect of PMTUD		4.5. Disabling the Effect of PMTUD
	A PL implementing this specification MUST suspend network layer		A PL implementing this specification MUST suspend network layer
	processing of outgoing packets that enforces a PMTU		processing of outgoing packets that enforces a PMTU
	[RFC1191][RFC8201] for each flow utilising DPLPMTUD, and instead use		[RFC1191][RFC8201] for each flow utilizing DPLPMTUD, and instead use
	DPLPMTUD to control the size of packets that are sent by a flow.		DPLPMTUD to control the size of packets that are sent by a flow.
	This removes the need for the network layer to drop or fragment sent		This removes the need for the network layer to drop or fragment sent
	packets that have a size greater than the PMTU.		packets that have a size greater than the PMTU.
	4.6. Response to PTB Messages		4.6. Response to PTB Messages
	This method requires the DPLPMTUD sender to validate any received PTB		This method requires the DPLPMTUD sender to validate any received PTB
	message before using the PTB information. The response to a PTB		message before using the PTB information. The response to a PTB
	message depends on the PTB_SIZE indicated in the PTB message, the		message depends on the PL_PTB_SIZE calculated from the PTB_SIZE in
	state of the PLPMTUD state machine, and the IP protocol being used.		the PTB message, the state of the PLPMTUD state machine, and the IP
			protocol being used.
	Section 4.6.1 first describes validation for both IPv4 ICMP		Section 4.6.1 first describes validation for both IPv4 ICMP
	Unreachable messages (type 3) and ICMPv6 Packet Too Big messages,		Unreachable messages (type 3) and ICMPv6 Packet Too Big messages,
	both of which are referred to as PTB messages in this document.		both of which are referred to as PTB messages in this document.
	4.6.1. Validation of PTB Messages		4.6.1. Validation of PTB Messages
	This section specifies utilization of PTB messages.		This section specifies utilization of PTB messages.
	* A simple implementation MAY ignore received PTB messages and in		* A simple implementation MAY ignore received PTB messages and in
	skipping to change at page 18, line 14 ¶		skipping to change at page 18, line 20 ¶
	PL endpoints. A datagram application that uses well-known source and		PL endpoints. A datagram application that uses well-known source and
	destination ports ought to also rely on other information to complete		destination ports ought to also rely on other information to complete
	this validation.		this validation.
	These checks are intended to provide protection from packets that		These checks are intended to provide protection from packets that
	originate from a node that is not on the network path. A PTB message		originate from a node that is not on the network path. A PTB message
	that does not complete the validation MUST NOT be further utilized by		that does not complete the validation MUST NOT be further utilized by
	the DPLPMTUD method.		the DPLPMTUD method.
	PTB messages that have been validated MAY be utilized by the DPLPMTUD		PTB messages that have been validated MAY be utilized by the DPLPMTUD
	algorithm, but MUST NOT be used directly to set the PLPMTU. A method		algorithm, but MUST NOT be used directly to set the PLPMTU. The
	that utilizes these PTB messages can improve the speed at the which		PL_PTB_SIZE is smaller than the PTB_SIZE because it is reduced by
	the algorithm detects an appropriate PLPMTU by triggering an		headers below the PL including any IP options or extensions added to
	immediate probe for the PTB_SIZE, compared to one that relies solely		the PL packet. A method that utilizes these PTB messages can improve
	on probing using a timer-based search algorithm. Section 4.6.2		the speed at which the algorithm detects an appropriate PLPMTU by
	describes this processing.		triggering an immediate probe for the PL_PTB_SIZE (resulting in a
			network-layer packet of size PTB_SIZE), compared to one that relies
			solely on probing using a timer-based search algorithm.
			Section 4.6.2 describes this processing.
	4.6.2. Use of PTB Messages		4.6.2. Use of PTB Messages
	A set of checks are intended to provide protection from a router that		Before using the size reported in the PTB message it must first be
	reports an unexpected PTB_SIZE. The PL also needs to check that the		converted to a PL_PTB_SIZE. A set of checks are intended to provide
	indicated PTB_SIZE is less than the size used by probe packets and at		protection from a router that reports an unexpected PTB_SIZE. The PL
	least the minimum size accepted.		also needs to check that the indicated PL_PTB_SIZE is less than the
			size used by probe packets and at least the minimum size accepted.
	This section provides a summary of how PTB messages can be utilized.		This section provides a summary of how PTB messages can be utilized.
	This processing depends on the PTB_SIZE and the current value of a		This processing depends on the PL_PTB_SIZE and the current value of a
	set of variables:		set of variables:
	PTB_SIZE < MIN_PMTU		PL_PTB_SIZE < MIN_PLPMTU
	* Invalid PTB_SIZE see Section 4.6.1.		* Invalid PL_PTB_SIZE see Section 4.6.1.
	* PTB message ought to be discarded without further processing		* PTB message ought to be discarded without further processing
	(e. g. PLPMTU not modified).		(i.e., PLPMTU is not modified).
	* The information could be utilized as an input to trigger		* The information could be utilized as an input to a trigger that
	enabling a resilience mode.		would enable a resilience mode.
	MIN_PMTU < PTB_SIZE < BASE_PMTU		MIN_PLPMTU < PL_PTB_SIZE < BASE_PLPMTU
	* A robust PL MAY enter an error state (see Section 5.2) for an		* A robust PL MAY enter an error state (see Section 5.2) for an
	IPv4 path when the PTB_SIZE reported in the PTB message is		IPv4 path when the PL_PTB_SIZE reported in the PTB message is
	larger than or equal to 68 bytes [RFC0791] and when this is		larger than or equal to 68 bytes [RFC0791] and when this is
	less than the BASE_PMTU.		less than the BASE_PLPMTU.
	* A robust PL MAY enter an error state (see Section 5.2) for an		* A robust PL MAY enter an error state (see Section 5.2) for an
	IPv6 path when the PTB_SIZE reported in the PTB message is		IPv6 path when the PL_PTB_SIZE reported in the PTB message is
	larger than or equal to 1280 bytes [RFC8200] and when this is		larger than or equal to 1280 bytes [RFC8200] and when this is
	less than the BASE_PMTU.		less than the BASE_PLPMTU.
	PTB_SIZE = PLPMTU		PL_PTB_SIZE = PLPMTU
	* Completes the search for a larger PLPMTU.		* Completes the search for a larger PLPMTU.
	PTB_SIZE > PROBED_SIZE		PL_PTB_SIZE > PROBED_SIZE
	* Inconsistent network signal.		* Inconsistent network signal.
	* PTB message ought to be discarded without further processing		* PTB message ought to be discarded without further processing
	(e. g. PLPMTU not modified).		(i.e., PLPMTU is not modified).
	* The information could be utilized as an input to trigger		* The information could be utilized as an input to trigger
	enabling a resilience mode.		enabling a resilience mode.
	BASE_PMTU <= PTB_SIZE < PLPMTU		BASE_PLPMTU <= PL_PTB_SIZE < PLPMTU
	* This could be an indication of a black hole. The PLPMTU SHOULD		* This could be an indication of a black hole. The PLPMTU SHOULD
	be set to BASE_PMTU (the PLPMTU is reduced to the BASE_PMTU to		be set to BASE_PLPMTU (the PLPMTU is reduced to the BASE_PLPMTU
	avoid unnecessary packet loss when a black hole is		to avoid unnecessary packet loss when a black hole is
	encountered).		encountered).
	* The PL ought to start a search to quickly discover the new		* The PL ought to start a search to quickly discover the new
	PLPMTU. The PTB_SIZE reported in the PTB message can be used		PLPMTU. The PL_PTB_SIZE reported in the PTB message can be
	to initialize a search algorithm.		used to initialize a search algorithm.
	PLPMTU < PTB_SIZE < PROBED_SIZE		PLPMTU < PL_PTB_SIZE < PROBED_SIZE
	* The PLPMTU continues to be valid, but the last PROBED_SIZE		* The PLPMTU continues to be valid, but the size of a packet used
	searched was larger than the actual PMTU.		to search (PROBED_SIZE) was larger than the actual PMTU.
	* The PLPMTU is not updated.		* The PLPMTU is not updated.
	* The PL can use the reported PTB_SIZE from the PTB message as		* The PL can use the reported PL_PTB_SIZE from the PTB message as
	the next search point when it resumes the search algorithm.		the next search point when it resumes the search algorithm.
	5. Datagram Packetization Layer PMTUD		5. Datagram Packetization Layer PMTUD
	This section specifies Datagram PLPMTUD (DPLPMTUD). The method can		This section specifies Datagram PLPMTUD (DPLPMTUD). The method can
	be introduced at various points (as indicated with * in the figure		be introduced at various points (as indicated with * in the figure
	below) in the IP protocol stack to discover the PLPMTU so that an		below) in the IP protocol stack to discover the PLPMTU so that an
	application can utilize an appropriate MPS for the current network		application can utilize an appropriate MPS for the current network
	path.		path.
	DPLPMTUD SHOULD NOT be used by an upper PL or application if it is		DPLPMTUD SHOULD NOT be used by an upper PL or application if it is
	already used in a lower layer, DPLPMTUD SHOULD only be performed once		already used in a lower layer, DPLPMTUD SHOULD only be performed once
	between a pair of endpoints. A PL MUST adjust the MPS indicated by		between a pair of endpoints. A PL MUST adjust the MPS indicated by
	DPLPMTUD to account for any additional overhead introduced by the PL.		DPLPMTUD to account for any additional overhead introduced by the PL.
	+----------------------+		+----------------------+
	| Application* |		| Application* |
	+-+-------+----+----+--+		+-----+------------+---+
	| | | |		| |
	+---+--+ +--+--+ | +-+---+		+---+--+ +--+--+
	| QUIC*| |UDPO*| | |SCTP*|		| QUIC*| |SCTP*|
	+---+--+ +--+--+ | +--+--+		+---+--+ +-+-+-+
	| | | | |		| | |
	+-------+--+ | | |		+---+ +----+ |
	| | | |		| | |
	+-+-+--+ |		+-+--+-+ |
	| UDP | |		| UDP | |
	+---+--+ |		+---+--+ |
	| |		| |
	+--------------+-----+-+		+-----------+-------+--+
	| Network Interface |		| Network Interface |
	+----------------------+		+----------------------+
	Figure 2: Examples where DPLPMTUD can be implemented		Figure 2: Examples where DPLPMTUD can be implemented
	The central idea of DPLPMTUD is probing by a sender. Probe packets		The central idea of DPLPMTUD is probing by a sender. Probe packets
	are sent to find the maximum size of user message that can be		are sent to find the maximum size of user message that can be
	completely transferred across the network path from the sender to the		completely transferred across the network path from the sender to the
	destination.		destination.
	The following sections identify the components needed for		The following sections identify the components needed for
	implementation, provides an overview of the phases of operation, and		implementation, provides an overview of the phases of operation, and
	skipping to change at page 21, line 38 ¶		skipping to change at page 22, line 4 ¶
	An implementation could implement the various timers using a single		An implementation could implement the various timers using a single
	timer.		timer.
	5.1.2. Constants		5.1.2. Constants
	The following constants are defined:		The following constants are defined:
	MAX_PROBES: The MAX_PROBES is the maximum value of the PROBE_COUNT		MAX_PROBES: The MAX_PROBES is the maximum value of the PROBE_COUNT
	counter (see Section 5.1.3). MAX_PROBES represents the limit for		counter (see Section 5.1.3). MAX_PROBES represents the limit for
	the number of consecutive probe attempts of any size. Search		the number of consecutive probe attempts of any size. Search
	algorithms benefit from a MAX_PROBES value greater than 1 because		algorithms benefit from a MAX_PROBES valugreater than 1 because
	this can provide robustness to isolated packet loss. The default		this can provide robustness to isolated packet loss. The default
	value of MAX_PROBES is 3.		value of MAX_PROBES is 3.
	MIN_PMTU: The MIN_PMTU is the smallest allowed probe packet size.		MIN_PLPMTU: The MIN_PLPMTU is the smallest allowed probe packet
	For IPv6, this value is 1280 bytes, as specified in [RFC8200].		size. For IPv6, this value is 1280 bytes, as specified in
	For IPv4, the minimum value is 68 bytes.		[RFC8200]. For IPv4, the minimum value is 68 bytes.
	Note: An IPv4 router is required to be able to forward a datagram		Note: An IPv4 router is required to be able to forward a datagram
	of 68 bytes without further fragmentation. This is the combined		of 68 bytes without further fragmentation. This is the combined
	size of an IPv4 header and the minimum fragment size of 8 bytes.		size of an IPv4 header and the minimum fragment size of 8 bytes.
	In addition, receivers are required to be able to reassemble		In addition, receivers are required to be able to reassemble
	fragmented datagrams at least up to 576 bytes, as stated in		fragmented datagrams at least up to 576 bytes, as stated in
	section 3.3.3 of [RFC1122].		section 3.3.3 of [RFC1122].
	MAX_PMTU: The MAX_PMTU is the largest size of PLPMTU. This has to		MAX_PLPMTU: The MAX_PLPMTU is the largest size of PLPMTU. This has
	be less than or equal to the minimum of the local MTU of the		to be less than or equal to the maximum size of the PL packet that
	outgoing interface and the destination PMTU for receiving. An		can be sent on the outgoing interface (constrained by the local
	application, or PL, MAY choose a smaller MAX_PMTU when there is no		interface MTU). When known, this also ought to be less than the
	need to send packets larger than a specific size.		maximum size of PL packet that can be received by the remote
			endpoint (constrained by EMTU_R). It can be limited by the design
			or configuration of the PL being used. An application, or PL, MAY
			choose a smaller MAX_PLPMTU when there is no need to send packets
			larger than a specific size.
	BASE_PMTU: The BASE_PMTU is a configured size expected to work for		BASE_PLPMTU: The BASE_PLPMTU is a configured size expected to work
	most paths. The size is equal to or larger than the MIN_PMTU and		for most paths. The size is equal to or larger than the
	smaller than the MAX_PMTU. In the case of IPv6, this value is		MIN_PLPMTU and smaller than the MAX_PLPMTU. In the case of IPv6,
	1280 bytes [RFC8200]. When using IPv4, a size of 1200 bytes is		this value is 1280 bytes [RFC8200]. When using IPv4, a size of
	RECOMMENDED.		1200 bytes is RECOMMENDED.
	5.1.3. Variables		5.1.3. Variables
	This method utilizes a set of variables:		This method utilizes a set of variables:
	PROBED_SIZE: The PROBED_SIZE is the size of the current probe		PROBED_SIZE: The PROBED_SIZE is the size of the current probe
	packet. This is a tentative value for the PLPMTU, which is		packet. This is a tentative value for the PLPMTU, which is
	awaiting confirmation by an acknowledgment.		awaiting confirmation by an acknowledgment.
	PROBE_COUNT: The PROBE_COUNT is a count of the number of successive		PROBE_COUNT: The PROBE_COUNT is a count of the number of successive
	skipping to change at page 22, line 34 ¶		skipping to change at page 23, line 4 ¶
	PROBE_COUNT: The PROBE_COUNT is a count of the number of successive		PROBE_COUNT: The PROBE_COUNT is a count of the number of successive
	unsuccessful probe packets that have been sent. Each time a probe		unsuccessful probe packets that have been sent. Each time a probe
	packet is acknowledged, the value is set to zero. (Some probe		packet is acknowledged, the value is set to zero. (Some probe
	loss is expected while searching, therefore loss of a single probe		loss is expected while searching, therefore loss of a single probe
	is not an indication of a PMTU problem.)		is not an indication of a PMTU problem.)
	The figure below illustrates the relationship between the packet size		The figure below illustrates the relationship between the packet size
	constants and variables at a point of time when the DPLPMTUD		constants and variables at a point of time when the DPLPMTUD
	algorithm performs path probing to increase the size of the PLPMTU.		algorithm performs path probing to increase the size of the PLPMTU.
	A probe packet has been sent of size PROBED_SIZE. Once this is		A probe packet has been sent of size PROBED_SIZE. Once this is
	acknowledged, the PLPMTU will raise to PROBED_SIZE allowing the		acknowledged, the PLPMTU will raise to PROBED_SIZE allowing the
	DPLPMTUD algorithm to further increase PROBED_SIZE towards the actual		DPLPMTUD algorithm to further increase PROBED_SIZE toward sending a
	PMTU.		probe with the size of the actual PMTU.
	MIN_PMTU MAX_PMTU		MIN_PLPMTU MAX_PLPMTU
	<-------------------------------------------------->		<------------------------------------------->
	| | | |		| | |
	v | | v		v | |
	BASE_PMTU | v Actual PMTU		BASE_PLPMTU | v
	| PROBED_SIZE		| PROBED_SIZE
	v		v
	PLPMTU		PLPMTU
	Figure 3: Relationships between packet size constants and variables		Figure 3: Relationships between packet size constants and variables
	5.1.4. Overview of DPLPMTUD Phases		5.1.4. Overview of DPLPMTUD Phases
	This section provides a high-level informative view of the DPLPMTUD		This section provides a high-level informative view of the DPLPMTUD
	method, by describing the movement of the method through several		method, by describing the movement of the method through several
	phases of operation. More detail is available in the state machine		phases of operation. More detail is available in the state machine
	Section 5.2.		Section 5.2.
	+------+		+------+
	+------->| Base |----------------+ Connectivity		+------->| Base |-----------------+ Connectivity
	| +------+ | or BASE_PMTU		| +------+ | or BASE_PLPMTU
	| | | confirmation failed		| | | confirmation failed
	| | v		| | v
	| | Connectivity +-------+		| | Connectivity +-------+
	| | and BASE_PMTU | Error |		| | and BASE_PLPMTU | Error |
	| | confirmed +-------+		| | confirmed +-------+
	| | | Consistent		| | | Consistent
	| v | connectivity		| v | connectivity
	PLPMTU | +--------+ | and BASE_PMTU		PLPMTU | +--------+ | and BASE_PLPMTU
	confirmation | | Search |<--------------+ confirmed		confirmation | | Search |<---------------+ confirmed
	failed | +--------+		failed | +--------+
	| ^ |		| ^ |
	| | |		| | |
	| Raise | | Search		| Raise | | Search
	| timer | | algorithm		| timer | | algorithm
	| expired | | completed		| expired | | completed
	| | |		| | |
	| | v		| | v
	| +-----------------+		| +-----------------+
	+---| Search Complete |		+---| Search Complete |
	+-----------------+		+-----------------+
	Figure 4: DPLPMTUD Phases		Figure 4: DPLPMTUD Phases
	Base: The Base Phase confirms connectivity to the remote peer using		Base: The Base Phase confirms connectivity to the remote peer using
	packets of the BASE_PMTU. This phase is implicit for a		packets of the BASE_PLPMTU. This phase is implicit for a
	connection-oriented PL (where it can be performed in a PL		connection-oriented PL (where it can be performed in a PL
	connection handshake). A connectionless PL sends an acknowledged		connection handshake). A connectionless PL sends a probe packet
	probe packet to confirm that the remote peer is reachable. The		and uses acknowledgment of this probe packet to confirm that the
	sender also confirms that BASE_PMTU is supported across the		remote peer is reachable.
	network path.
			The sender also confirms that BASE_PLPMTU is supported across the
			network path. This may be achieved using a PL mechanism (e.g.,
			using a handshake packet of size BASE_PLPMTU), or by sending a
			probe packet of size BASE_PLPMTU and confirming that this is
			received.
			A probe packet of size BASE_PLPMTU can be sent immediately on the
			initial entry to the Base Phase (following a connectivity check).
	A PL that does not wish to support a path with a PLPMTU less than		A PL that does not wish to support a path with a PLPMTU less than
	BASE_PMTU can simplify the phase into a single step by performing		BASE_PLPMTU can simplify the phase into a single step by
	the connectivity checks with a probe of the BASE_PMTU size.		performing the connectivity checks with a probe of the BASE_PLPMTU
			size.
	Once confirmed, DPLPMTUD enters the Search Phase. If this phase		Once confirmed, DPLPMTUD enters the Search Phase. If this phase
	fails to confirm, DPLPMTUD enters the Error Phase.		fails to confirm, DPLPMTUD enters the Error Phase.
	Search: The Search Phase utilizes a search algorithm to send probe		Search: The Search Phase utilizes a search algorithm to send probe
	packets to seek to increase the PLPMTU. The algorithm concludes		packets to seek to increase the PLPMTU. The algorithm concludes
	when it has found a suitable PLPMTU, by entering the Search		when it has found a suitable PLPMTU, by entering the Search
	Complete Phase.		Complete Phase.
	A PL could respond to PTB messages using the PTB to advance or		A PL could respond to PTB messages using the PTB to advance or
	skipping to change at page 24, line 25 ¶		skipping to change at page 24, line 48 ¶
	CONFIRMATION_TIMER to periodically repeat a probe packet for the		CONFIRMATION_TIMER to periodically repeat a probe packet for the
	current PLPMTU size. If the sender is unable to confirm		current PLPMTU size. If the sender is unable to confirm
	reachability (e.g., if the CONFIRMATION_TIMER expires) or the PL		reachability (e.g., if the CONFIRMATION_TIMER expires) or the PL
	signals a lack of reachability, DPLPMTUD enters the Base phase.		signals a lack of reachability, DPLPMTUD enters the Base phase.
	The PMTU_RAISE_TIMER is used to periodically resume the search		The PMTU_RAISE_TIMER is used to periodically resume the search
	phase to discover if the PLPMTU can be raised. Black Hole		phase to discover if the PLPMTU can be raised. Black Hole
	Detection causes the sender to enter the Base Phase.		Detection causes the sender to enter the Base Phase.
	Error: The Error Phase is entered when there is conflicting or		Error: The Error Phase is entered when there is conflicting or
	invalid PLPMTU information for the path (e.g. a failure to support		invalid PLPMTU information for the path (e.g., a failure to
	the BASE_PMTU) that cause DPLPMTUD to be unable to progress and		support the BASE_PLPMTU) that cause DPLPMTUD to be unable to
	the PLPMTU is lowered.		progress and the PLPMTU is lowered.
	DPLPMTUD remains in the Error Phase until a consistent view of the		DPLPMTUD remains in the Error Phase until a consistent view of the
	path can be discovered and it has also been confirmed that the		path can be discovered and it has also been confirmed that the
	path supports the BASE_PMTU (or DPLPMTUD is suspended).		path supports the BASE_PLPMTU (or DPLPMTUD is suspended).
	An implementation that only reduces the PLPMTU to a suitable size		An implementation that only reduces the PLPMTU to a suitable size
	would be sufficient to ensure reliable operation, but can be very		would be sufficient to ensure reliable operation, but can be very
	inefficient when the actual PMTU changes or when the method (for		inefficient when the actual PMTU changes or when the method (for
	whatever reason) makes a suboptimal choice for the PLPMTU.		whatever reason) makes a suboptimal choice for the PLPMTU.
	A full implementation of DPLPMTUD provides an algorithm enabling the		A full implementation of DPLPMTUD provides an algorithm enabling the
	DPLPMTUD sender to increase the PLPMTU following a change in the		DPLPMTUD sender to increase the PLPMTU following a change in the
	characteristics of the path, such as when a link is reconfigured with		characteristics of the path, such as when a link is reconfigured with
	a larger MTU, or when there is a change in the set of links traversed		a larger MTU, or when there is a change in the set of links traversed
	skipping to change at page 25, line 13 ¶		skipping to change at page 26, line 13 ¶
	Note: Not all changes are shown to simplify the diagram.		Note: Not all changes are shown to simplify the diagram.
	| |		| |
	| Start | PL indicates loss		| Start | PL indicates loss
	| | of connectivity		| | of connectivity
	v v		v v
	+---------------+ +---------------+		+---------------+ +---------------+
	| DISABLED | | ERROR |		| DISABLED | | ERROR |
	+---------------+ PROBE_TIMER expiry: +---------------+		+---------------+ PROBE_TIMER expiry: +---------------+
	| PL indicates PROBE_COUNT = MAX_PROBES or ^ |		| PL indicates PROBE_COUNT = MAX_PROBES or ^ |
	| connectivity PTB: PTB_SIZE < BASE_PMTU | |		| connectivity PTB: PLPTB_SIZE < BASE_PLPMTU | |
	+--------------------+ +---------------+ |		+--------------------+ +---------------+ |
	| | |		| | |
	v | BASE_PMTU Probe |		v | BASE_PLPMTU Probe |
	+---------------+ acked |		+---------------+ acked |
	| BASE |----------------------+		| BASE |----------------------+
	+---------------+ |		+---------------+ |
	^ | ^ ^ |		^ | ^ ^ |
	Black hole detected | | | | Black hole detected |		Black hole detected | | | | Black hole detected |
	+--------------------+ | | +--------------------+ |		+--------------------+ | | +--------------------+ |
	| +----+ | |		| +----+ | |
	| PROBE_TIMER expiry: | |		| PROBE_TIMER expiry: | |
	| PROBE_COUNT < MAX_PROBES | |		| PROBE_COUNT < MAX_PROBES | |
	| | |		| | |
	| PMTU_RAISE_TIMER expiry | |		| PMTU_RAISE_TIMER expiry | |
	| +-----------------------------------------+ | |		| +-----------------------------------------+ | |
	| | | | |		| | | | |
	| | v | v		| | v | v
	+---------------+ +---------------+		+---------------+ +---------------+
	|SEARCH_COMPLETE| | SEARCHING |		|SEARCH_COMPLETE| | SEARCHING |
	+---------------+ +---------------+		+---------------+ +---------------+
	| ^ ^ | | ^		| ^ ^ | | ^
	| | | | | |		| | | | | |
	| | +-----------------------------------------+ | |		| | +-----------------------------------------+ | |
	| | MAX_PMTU Probe acked or | |		| | MAX_PLPMTU Probe acked or | |
	| | PROBE_TIMER expiry: PROBE_COUNT = MAX_PROBES or | |		| | PROBE_TIMER expiry: PROBE_COUNT = MAX_PROBES or | |
	+----+ PTB: PTB_SIZE = PLPMTU +----+		+----+ PTB: PLPTB_SIZE = PLPMTU +----+
	CONFIRMATION_TIMER expiry: PROBE_TIMER expiry:		CONFIRMATION_TIMER expiry: PROBE_TIMER expiry:
	PROBE_COUNT < MAX_PROBES or PROBE_COUNT < MAX_PROBES or		PROBE_COUNT < MAX_PROBES or PROBE_COUNT < MAX_PROBES or
	PLPMTU Probe acked Probe acked or PTB:		PLPMTU Probe acked Probe acked or PTB:
	PLPMTU < PTB_SIZE < PROBED_SIZE		PLPMTU < PLPTB_SIZE < PROBED_SIZE
	Figure 5: State machine for Datagram PLPMTUD		Figure 5: State machine for Datagram PLPMTUD
	The following states are defined:		The following states are defined:
	DISABLED: The DISABLED state is the initial state before probing has		DISABLED: The DISABLED state is the initial state before probing has
	started. It is also entered from any other state, when the PL		started. It is also entered from any other state, when the PL
	indicates loss of connectivity. This state is left, once the PL		indicates loss of connectivity. This state is left once the PL
	indicates connectivity to the remote PL.		indicates connectivity to the remote PL. When transitioning to
			the BASE state, a probe packet of size BASE_PLPMTU can be sent
			immediately.
	BASE: The BASE state is used to confirm that the BASE_PMTU size is		BASE: The BASE state is used to confirm that the BASE_PLPMTU size is
	supported by the network path and is designed to allow an		supported by the network path and is designed to allow an
	application to continue working when there are transient		application to continue working when there are transient
	reductions in the actual PMTU. It also seeks to avoid long		reductions in the actual PMTU. It also seeks to avoid long
	periods when a sender searching for a larger PLPMTU is unaware		periods when a sender searching for a larger PLPMTU is unaware
	that packets are not being delivered due to a packet or ICMP Black		that packets are not being delivered due to a packet or ICMP Black
	Hole.		Hole.
	On entry, the PROBED_SIZE is set to the BASE_PMTU size and the		On entry, the PROBED_SIZE is set to the BASE_PLPMTU size and the
	PROBE_COUNT is set to zero.		PROBE_COUNT is set to zero.
	Each time a probe packet is sent, the PROBE_TIMER is started. The		Each time a probe packet is sent, the PROBE_TIMER is started. The
	state is exited when the probe packet is acknowledged, and the PL		state is exited when the probe packet is acknowledged, and the PL
	sender enters the SEARCHING state.		sender enters the SEARCHING state.
	The state is also left when the PROBE_COUNT reaches MAX_PROBES or		The state is also left when the PROBE_COUNT reaches MAX_PROBES or
	a received PTB message is validated. This causes the PL sender to		a received PTB message is validated. This causes the PL sender to
	enter the ERROR state.		enter the ERROR state.
	SEARCHING: The SEARCHING state is the main probing state. This		SEARCHING: The SEARCHING state is the main probing state. This
	state is entered when probing for the BASE_PMTU was successful.		state is entered when probing for the BASE_PLPMTU was successful.
	Each time a probe packet is acknowledged, the PROBE_COUNT is set		Each time a probe packet is acknowledged, the PROBE_COUNT is set
	to zero, the PLPMTU is set to the PROBED_SIZE and then the		to zero, the PLPMTU is set to the PROBED_SIZE and then the
	PROBED_SIZE is increased using the search algorithm.		PROBED_SIZE is increased using the search algorithm.
	When a probe packet is sent and not acknowledged within the period		When a probe packet is sent and not acknowledged within the period
	of the PROBE_TIMER, the PROBE_COUNT is incremented and a new probe		of the PROBE_TIMER, the PROBE_COUNT is incremented and a new probe
	packet is transmitted.		packet is transmitted.
	The state is exited to enter SEARCH_COMPLETE when the PROBE_COUNT		The state is exited to enter SEARCH_COMPLETE when the PROBE_COUNT
	reaches MAX_PROBES, a validated PTB is received that corresponds		reaches MAX_PROBES, a validated PTB is received that corresponds
	to the last successfully probed size (PTB_SIZE = PLPMTU), or a		to the last successfully probed size (PL_PTB_SIZE = PLPMTU), or a
	probe of size MAX_PMTU is acknowledged (PLPMTU = MAX_PMTU).		probe of size MAX_PLPMTU is acknowledged (PLPMTU = MAX_PLPMTU).
	When a black hole is detected in the SEARCHING state, this causes		When a black hole is detected in the SEARCHING state, this causes
	the PL sender to enter the BASE state.		the PL sender to enter the BASE state.
	SEARCH_COMPLETE: The SEARCH_COMPLETE state indicates a successful		SEARCH_COMPLETE: The SEARCH_COMPLETE state indicates a successful
	end to the SEARCHING state. DPLPMTUD remains in this state until		end to the SEARCHING state. DPLPMTUD remains in this state until
	either the PMTU_RAISE_TIMER expires or a black hole is detected.		either the PMTU_RAISE_TIMER expires or a black hole is detected.
	When DPLPMTUD uses an unacknowledged PL and is in the		When DPLPMTUD uses an unacknowledged PL and is in the
	SEARCH_COMPLETE state, a CONFIRMATION_TIMER periodically resets		SEARCH_COMPLETE state, a CONFIRMATION_TIMER periodically resets
	the PROBE_COUNT and schedules a probe packet with the size of the		the PROBE_COUNT and schedules a probe packet with the size of the
	PLPMTU. If MAX_PROBES successive PLPMTUD sized probes fail to be		PLPMTU. If MAX_PROBES successive PLPMTUD sized probes fail to be
	acknowledged the method enters the BASE state. When used with an		acknowledged the method enters the BASE state. When used with an
	acknowledged PL (e.g., SCTP), DPLPMTUD SHOULD NOT continue to		acknowledged PL (e.g., SCTP), DPLPMTUD SHOULD NOT continue to
	generate PLPMTU probes in this state.		generate PLPMTU probes in this state.
	ERROR: The ERROR state represents the case where either the network		ERROR: The ERROR state represents the case where either the network
	path is not known to support a PLPMTU of at least the BASE_PMTU		path is not known to support a PLPMTU of at least the BASE_PLPMTU
	size or when there is contradictory information about the network		size or when there is contradictory information about the network
	path that would otherwise result in excessive variation in the MPS		path that would otherwise result in excessive variation in the MPS
	signalled to the higher layer. The state implements a method to		signaled to the higher layer. The state implements a method to
	mitigate oscillation in the state-event engine. It signals a		mitigate oscillation in the state-event engine. It signals a
	conservative value of the MPS to the higher layer by the PL. The		conservative value of the MPS to the higher layer by the PL. The
	state is exited when packet probes no longer detect the error.		state is exited when packet probes no longer detect the error.
	The PL sender then enters the SEARCHING state.		The PL sender then enters the SEARCHING state.
	Implementations are permitted to enable endpoint fragmentation if		Implementations are permitted to enable endpoint fragmentation if
	the DPLPMTUD is unable to validate MIN_PMTU within PROBE_COUNT		the DPLPMTUD is unable to validate MIN_PLPMTU within PROBE_COUNT
	probes. If DPLPMTUD is unable to validate MIN_PMTU the		probes. If DPLPMTUD is unable to validate MIN_PLPMTU the
	implementation will transition to the DISABLED state.		implementation will transition to the DISABLED state.
	Note: MIN_PMTU could be identical to BASE_PMTU, simplifying the		Note: MIN_PLPMTU could be identical to BASE_PLPMTU, simplifying
	actions in this state.		the actions in this state.
	5.3. Search to Increase the PLPMTU		5.3. Search to Increase the PLPMTU
	This section describes the algorithms used by DPLPMTUD to search for		This section describes the algorithms used by DPLPMTUD to search for
	a larger PLPMTU.		a larger PLPMTU.
	5.3.1. Probing for a larger PLPMTU		5.3.1. Probing for a larger PLPMTU
	Implementations use a search algorithm across the search range to		Implementations use a search algorithm across the search range to
	determine whether a larger PLPMTU can be supported across a network		determine whether a larger PLPMTU can be supported across a network
	path.		path.
	The method discovers the search range by confirming the minimum		The method discovers the search range by confirming the minimum
	PLPMTU and then using the probe method to select a PROBED_SIZE less		PLPMTU and then using the probe method to select a PROBED_SIZE less
	than or equal to MAX_PMTU. MAX_PMTU is the minimum of the local MTU		than or equal to MAX_PLPMTU. MAX_PLPMTU is the minimum of the local
	and EMTU_R (learned from the remote endpoint). The MAX_PMTU MAY be		MTU and EMTU_R (when this is learned from the remote endpoint). The
	reduced by an application that sets a maximum to the size of		MAX_PLPMTU MAY be reduced by an application that sets a maximum to
	datagrams it will send.		the size of datagrams it will send.
	The PROBE_COUNT is initialized to zero when the first probe with a		The PROBE_COUNT is initialized to zero when the first probe with a
	size greater than or equal to PLPMTUD is sent. A timer is used to		size greater than or equal to PLPMTUD is sent. A timer is used to
	trigger the sending of probe packets of size PROBED_SIZE, larger than		trigger the sending of probe packets of size PROBED_SIZE, larger than
	the PLPMTU. Each probe packet successfully sent to the remote peer		the PLPMTU. Each probe packet successfully sent to the remote peer
	is confirmed by acknowledgement at the PL, see Section 4.1.		is confirmed by acknowledgment at the PL, see Section 4.1.
	Each time a probe packet is sent to the destination, the PROBE_TIMER		Each time a probe packet is sent to the destination, the PROBE_TIMER
	is started. The timer is canceled when the PL receives		is started. The timer is canceled when the PL receives
	acknowledgment that the probe packet has been successfully sent		acknowledgment that the probe packet has been successfully sent
	across the path Section 4.1. This confirms that the PROBED_SIZE is		across the path Section 4.1. This confirms that the PROBED_SIZE is
	supported, and the PROBED_SIZE value is then assigned to the PLPMTU.		supported, and the PROBED_SIZE value is then assigned to the PLPMTU.
	The search algorithm can continue to send subsequent probe packets of		The search algorithm can continue to send subsequent probe packets of
	an increasing size.		an increasing size.
	If the timer expires before a probe packet is acknowledged, the probe		If the timer expires before a probe packet is acknowledged, the probe
	skipping to change at page 29, line 9 ¶		skipping to change at page 30, line 9 ¶
	A PL sender is able to detect inconsistency from the sequence of		A PL sender is able to detect inconsistency from the sequence of
	PLPMTU probes that are acknowledged or the sequence of PTB messages		PLPMTU probes that are acknowledged or the sequence of PTB messages
	that it receives. When inconsistent path information is detected, a		that it receives. When inconsistent path information is detected, a
	PL sender could use an alternate search mode that clamps the offered		PL sender could use an alternate search mode that clamps the offered
	MPS to a smaller value for a period of time. This avoids unnecessary		MPS to a smaller value for a period of time. This avoids unnecessary
	loss of packets.		loss of packets.
	5.4. Robustness to Inconsistent Paths		5.4. Robustness to Inconsistent Paths
	Some paths could be unable to sustain packets of the BASE_PMTU size.		Some paths could be unable to sustain packets of the BASE_PLPMTU
	To be robust to these paths an implementation could implement the		size. To be robust to these paths an implementation could implement
	Error State. This allows fallback to a smaller than desired PLPMTU,		the Error State. This allows fallback to a smaller than desired
	rather than suffer connectivity failure. This could utilize methods		PLPMTU, rather than suffer connectivity failure. This could utilize
	such as endpoint IP fragmentation to enable the PL sender to		methods such as endpoint IP fragmentation to enable the PL sender to
	communicate using packets smaller than the BASE_PMTU.		communicate using packets smaller than the BASE_PLPMTU.
	6. Specification of Protocol-Specific Methods		6. Specification of Protocol-Specific Methods
	DPLPMTUD requires protocol-specific details to be specified for each		DPLPMTUD requires protocol-specific details to be specified for each
	PL that is used.		PL that is used.
	The first subsection provides guidance on how to implement the		The first subsection provides guidance on how to implement the
	DPLPMTUD method as a part of an application using UDP or UDP-Lite.		DPLPMTUD method as a part of an application using UDP or UDP-Lite.
	The guidance also applies to other datagram services that do not		The guidance also applies to other datagram services that do not
	include a specific transport protocol (such as a tunnel		include a specific transport protocol (such as a tunnel
	skipping to change at page 30, line 8 ¶		skipping to change at page 31, line 8 ¶
	In addition, it is desirable that PMTU discovery is not performed by		In addition, it is desirable that PMTU discovery is not performed by
	multiple protocol layers. An application SHOULD avoid using DPLPMTUD		multiple protocol layers. An application SHOULD avoid using DPLPMTUD
	when the underlying transport system provides this capability. To		when the underlying transport system provides this capability. To
	use common method for managing the PLPMTU has benefits, both in the		use common method for managing the PLPMTU has benefits, both in the
	ability to share state between different processes and opportunities		ability to share state between different processes and opportunities
	to coordinate probing.		to coordinate probing.
	6.1.1. Application Request		6.1.1. Application Request
	An application needs an application-layer protocol mechanism (such as		An application needs an application-layer protocol mechanism (such as
	a message acknowledgement method) that solicits a response from a		a message acknowledgment method) that solicits a response from a
	destination endpoint. The method SHOULD allow the sender to check		destination endpoint. The method SHOULD allow the sender to check
	the value returned in the response to provide additional protection		the value returned in the response to provide additional protection
	from off-path insertion of data [RFC8085], suitable methods include a		from off-path insertion of data [RFC8085], suitable methods include a
	parameter known only to the two endpoints, such as a session ID or		parameter known only to the two endpoints, such as a session ID or
	initialized sequence number.		initialized sequence number.
	6.1.2. Application Response		6.1.2. Application Response
	An application needs an application-layer protocol mechanism to		An application needs an application-layer protocol mechanism to
	communicate the response from the destination endpoint. This		communicate the response from the destination endpoint. This
	response could indicate successful reception of the probe across the		response could indicate successful reception of the probe across the
	path, but could also indicate that some (or all packets) have failed		path, but could also indicate that some (or all packets) have failed
	to reach the destination.		to reach the destination.
	6.1.3. Sending Application Probe Packets		6.1.3. Sending Application Probe Packets
	A probe packet that could carry an application data block, but the		A probe packet can carry an application data block, but the
	successful transmission of this data is at risk when used for		successful transmission of this data is at risk when used for
	probing. Some applications might prefer to use a probe packet that		probing. Some applications might prefer to use a probe packet that
	does not carry an application data block to avoid disruption to data		does not carry an application data block to avoid disruption to data
	transfer.		transfer.
	6.1.4. Initial Connectivity		6.1.4. Initial Connectivity
	An application that does not have other higher-layer information		An application that does not have other higher-layer information
	confirming connectivity with the remote peer SHOULD implement a		confirming connectivity with the remote peer SHOULD implement a
	connectivity mechanism using acknowledged probe packets before		connectivity mechanism using acknowledged probe packets before
	skipping to change at page 30, line 49 ¶		skipping to change at page 31, line 49 ¶
	An application that does not have other higher-layer information		An application that does not have other higher-layer information
	confirming correct delivery of datagrams SHOULD implement the		confirming correct delivery of datagrams SHOULD implement the
	CONFIRMATION_TIMER to periodically send probe packets while in the		CONFIRMATION_TIMER to periodically send probe packets while in the
	SEARCH_COMPLETE state.		SEARCH_COMPLETE state.
	6.1.6. Handling of PTB Messages		6.1.6. Handling of PTB Messages
	An application that is able and wishes to receive PTB messages MUST		An application that is able and wishes to receive PTB messages MUST
	perform ICMP validation as specified in Section 5.2 of [RFC8085].		perform ICMP validation as specified in Section 5.2 of [RFC8085].
	This requires that the application to check each received PTB		This requires that the application checks each received PTB message
	messages to validate it is received in response to transmitted		to validate that it was is received in response to transmitted
	traffic and that the reported PTB_SIZE is less than the current		traffic and that the reported PL_PTB_SIZE is less than the current
	probed size (see Section 4.6.2). A validated PTB message MAY be used		probed size (see Section 4.6.2). A validated PTB message MAY be used
	as input to the DPLPMTUD algorithm, but MUST NOT be used directly to		as input to the DPLPMTUD algorithm, but MUST NOT be used directly to
	set the PLPMTU.		set the PLPMTU.
	6.2. DPLPMTUD for SCTP		6.2. DPLPMTUD for SCTP
	Section 10.2 of [RFC4821] specified a recommended PLPMTUD probing		Section 10.2 of [RFC4821] specified a recommended PLPMTUD probing
	method for SCTP and Section 7.3 of [RFC4960] and recommended an		method for SCTP and Section 7.3 of [RFC4960] and recommended an
	endpoint apply the techniques in RFC4821 on a per-destination-address		endpoint apply the techniques in RFC4821 on a per-destination-address
	basis. The specification for DPLPMTUD continues the practice of		basis. The specification for DPLPMTUD continues the practice of
	skipping to change at page 32, line 10 ¶		skipping to change at page 33, line 10 ¶
	The HEARTBEAT chunk carries a Heartbeat Information parameter which		The HEARTBEAT chunk carries a Heartbeat Information parameter which
	includes, besides the information suggested in [RFC4960], the probe		includes, besides the information suggested in [RFC4960], the probe
	size, which is the size of the complete datagram. The size of the		size, which is the size of the complete datagram. The size of the
	PAD chunk is therefore computed by reducing the probing size by the		PAD chunk is therefore computed by reducing the probing size by the
	IPv4 or IPv6 header size, the SCTP common header, the HEARTBEAT		IPv4 or IPv6 header size, the SCTP common header, the HEARTBEAT
	request and the PAD chunk header. The payload of the PAD chunk		request and the PAD chunk header. The payload of the PAD chunk
	contains arbitrary data.		contains arbitrary data.
	Probing starts directly after the PL handshake, before data is sent.		Probing starts directly after the PL handshake, before data is sent.
	Assuming this behavior (i.e., the PMTU is smaller than or equal to		Assuming this behavior (i.e., the PMTU is smaller than or equal to
	the interface MTU), this process will take a few round trip time		the interface MTU), this process will take several round trip time
	periods, dependent on the number of PMTU probes sent. The Heartbeat		periods, dependent on the number of DPLPMTUD probes sent. The
	timer can be used to implement the PROBE_TIMER.		Heartbeat timer can be used to implement the PROBE_TIMER.
	6.2.1.3. Validating the Path with SCTP		6.2.1.3. Validating the Path with SCTP
	Since SCTP provides an acknowledged PL, a sender MUST NOT implement		Since SCTP provides an acknowledged PL, a sender MUST NOT implement
	the CONFIRMATION_TIMER while in the SEARCH_COMPLETE state.		the CONFIRMATION_TIMER while in the SEARCH_COMPLETE state.
	6.2.1.4. PTB Message Handling by SCTP		6.2.1.4. PTB Message Handling by SCTP
	Normal ICMP validation MUST be performed as specified in Appendix C		Normal ICMP validation MUST be performed as specified in Appendix C
	of [RFC4960]. This requires that the first 8 bytes of the SCTP		of [RFC4960]. This requires that the first 8 bytes of the SCTP
	common header are quoted in the payload of the PTB message, which can		common header are quoted in the payload of the PTB message, which can
	be the case for ICMPv4 and is normally the case for ICMPv6.		be the case for ICMPv4 and is normally the case for ICMPv6.
	When a PTB message has been validated, the PTB_SIZE reported in the		When a PTB message has been validated, the PL_PTB_SIZE calculated
	PTB message SHOULD be used with the DPLPMTUD algorithm, providing		from the PTB_SIZE reported in the PTB message SHOULD be used with the
	that the reported PTB_SIZE is less than the current probe size (see		DPLPMTUD algorithm, providing that the reported PL_PTB_SIZE is less
	Section 4.6).		than the current probe size (see Section 4.6).
	6.2.2. DPLPMTUD for SCTP/UDP		6.2.2. DPLPMTUD for SCTP/UDP
	The UDP encapsulation of SCTP is specified in [RFC6951].		The UDP encapsulation of SCTP is specified in [RFC6951].
	This specification updates the reference to RFC 4821 in section 5.6		This specification updates the reference to RFC 4821 in section 5.6
	of RFC 6951 to refer to XXXTHISRFCXXX. RFC 6951 is updated by		of RFC 6951 to refer to XXXTHISRFCXXX. RFC 6951 is updated by
	addition of the following sentence is to be added at the end of		addition of the following sentence is to be added at the end of
	section 5.6: "The RECOMMENDED method for determining the MTU of the		section 5.6: "The RECOMMENDED method for determining the MTU of the
	path is specified in XXXTHISRFCXXX".		path is specified in XXXTHISRFCXXX".
	skipping to change at page 33, line 23 ¶		skipping to change at page 34, line 23 ¶
	Since SCTP provides an acknowledged PL, a sender MUST NOT implement		Since SCTP provides an acknowledged PL, a sender MUST NOT implement
	the CONFIRMATION_TIMER while in the SEARCH_COMPLETE state.		the CONFIRMATION_TIMER while in the SEARCH_COMPLETE state.
	6.2.2.4. Handling of PTB Messages by SCTP/UDP		6.2.2.4. Handling of PTB Messages by SCTP/UDP
	ICMP validation MUST be performed for PTB messages as specified in		ICMP validation MUST be performed for PTB messages as specified in
	Appendix C of [RFC4960]. This requires that the first 8 bytes of the		Appendix C of [RFC4960]. This requires that the first 8 bytes of the
	SCTP common header are contained in the PTB message, which can be the		SCTP common header are contained in the PTB message, which can be the
	case for ICMPv4 (but note the UDP header also consumes a part of the		case for ICMPv4 (but note the UDP header also consumes a part of the
	quoted packet header) and is normally the case for ICMPv6. When the		quoted packet header) and is normally the case for ICMPv6. When the
	validation is completed, the PTB_SIZE indicated in the PTB message		validation is completed, the PL_PTB_SIZE calculated from the PTB_SIZE
	SHOULD be used with the DPLPMTUD providing that the reported PTB_SIZE		in the PTB message SHOULD be used with the DPLPMTUD providing that
	is less than the current probe size.		the reported PL_PTB_SIZE is less than the current probe size.
	6.2.3. DPLPMTUD for SCTP/DTLS		6.2.3. DPLPMTUD for SCTP/DTLS
	The Datagram Transport Layer Security (DTLS) encapsulation of SCTP is		The Datagram Transport Layer Security (DTLS) encapsulation of SCTP is
	specified in [RFC8261] . This is used for data channels in WebRTC		specified in [RFC8261]. This is used for data channels in WebRTC
	implementations. This specification updates the reference to RFC		implementations. This specification updates the reference to RFC
	4821 in section 5 of RFC 8261 to refer to XXXTHISRFCXXX.		4821 in section 5 of RFC 8261 to refer to XXXTHISRFCXXX.
	XXX RFC EDITOR - please replace XXXTHISRFCXXX when published XXX		XXX RFC EDITOR - please replace XXXTHISRFCXXX when published XXX
	6.2.3.1. Initial Connectivity		6.2.3.1. Initial Connectivity
	A sender can enter the BASE state as soon as SCTP connectivity has		A sender can enter the BASE state as soon as SCTP connectivity has
	been confirmed.		been confirmed.
	skipping to change at page 34, line 21 ¶		skipping to change at page 35, line 21 ¶
	QUIC [I-D.ietf-quic-transport] is a UDP-based transport that provides		QUIC [I-D.ietf-quic-transport] is a UDP-based transport that provides
	reception feedback. The UDP payload includes the QUIC packet header,		reception feedback. The UDP payload includes the QUIC packet header,
	protected payload, and any authentication fields. QUIC depends on a		protected payload, and any authentication fields. QUIC depends on a
	PMTU of at least 1280 bytes.		PMTU of at least 1280 bytes.
	Section 14 of [I-D.ietf-quic-transport] describes the path		Section 14 of [I-D.ietf-quic-transport] describes the path
	considerations when sending QUIC packets. It recommends the use of		considerations when sending QUIC packets. It recommends the use of
	PADDING frames to build the probe packet. Pure probe-only packets		PADDING frames to build the probe packet. Pure probe-only packets
	are constructed with PADDING frames and PING frames to create a		are constructed with PADDING frames and PING frames to create a
	padding only packet that will elicit an acknowledgement. Such		padding only packet that will elicit an acknowledgment. Such padding
	padding only packets enable probing without affecting the transfer of		only packets enable probing without affecting the transfer of other
	other QUIC frames.		QUIC frames.
	The recommendation for QUIC endpoints implementing DPLPMTUD is that a		The recommendation for QUIC endpoints implementing DPLPMTUD is that a
	MPS is maintained for each combination of local and remote IP		MPS is maintained for each combination of local and remote IP
	addresses [I-D.ietf-quic-transport]. If a QUIC endpoint determines		addresses [I-D.ietf-quic-transport]. If a QUIC endpoint determines
	that the PMTU between any pair of local and remote IP addresses has		that the PMTU between any pair of local and remote IP addresses has
	fallen below an acceptable MPS, it immediately ceases to send QUIC		fallen below the size required for an acceptable MPS, it immediately
	packets on the affected path. This could result in termination of		ceases to send QUIC packets on the affected path. This could result
	the connection if an alternative path cannot be found		in termination of the connection if an alternative path cannot be
	[I-D.ietf-quic-transport].		found [I-D.ietf-quic-transport].
	6.3.1. Initial Connectivity		6.3.1. Initial Connectivity
	The base protocol is specified in [I-D.ietf-quic-transport]. This		The base protocol is specified in [I-D.ietf-quic-transport]. This
	provides an acknowledged PL. A sender can therefore enter the BASE		provides an acknowledged PL. A sender can therefore enter the BASE
	state as soon as connectivity has been confirmed.		state as soon as connectivity has been confirmed.
	6.3.2. Sending QUIC Probe Packets		6.3.2. Sending QUIC Probe Packets
	A probe packet consists of a QUIC Header and a payload containing		A probe packet consists of a QUIC Header and a payload containing
	PADDING Frames and a PING Frame. PADDING Frames are a single octet		PADDING Frames and a PING Frame. PADDING Frames are a single octet
	(0x00) and several of these can be used to create a probe packet of		(0x00) and several of these can be used to create a probe packet of
	size PROBED_SIZE. QUIC provides an acknowledged PL, a sender can		size PROBED_SIZE. QUIC provides an acknowledged PL, a sender can
	therefore enter the BASE state as soon as connectivity has been		therefore enter the BASE state as soon as connectivity has been
	confirmed.		confirmed.
	The current specification of QUIC sets the following:		The current specification of QUIC sets the following:
	* BASE_PMTU: 1280. A QUIC sender pads initial packets to confirm		* BASE_PLPMTU: A QUIC sender pads initial packets to confirm the
	the path can support packets of the required size.		path can support packets of the required size, this sets the
			BASE_PLPMTU and MIN_PLPMTU.
	* MIN_PMTU: 1280 bytes. A QUIC sender that determines the PLPMTU		* MIN_PLPMTU: A QUIC sender that determines the MIN_PLPMTU has
	has fallen below 1280 bytes MUST immediately stop sending on the		fallen MUST immediately stop sending on the affected path.
	affected path.
	6.3.3. Validating the Path with QUIC		6.3.3. Validating the Path with QUIC
	QUIC provides an acknowledged PL. A sender therefore MUST NOT		QUIC provides an acknowledged PL. A sender therefore MUST NOT
	implement the CONFIRMATION_TIMER while in the SEARCH_COMPLETE state.		implement the CONFIRMATION_TIMER while in the SEARCH_COMPLETE state.
	6.3.4. Handling of PTB Messages by QUIC		6.3.4. Handling of PTB Messages by QUIC
	QUIC validates ICMP PTB messages. In addition to UDP Port		QUIC validates ICMP PTB messages. In addition to UDP Port
	validation, QUIC can validate an ICMP message by using other PL		validation, QUIC can validate an ICMP message by using other PL
	information (e.g., validation of connection IDs in the quoted packet		information (e.g., validation of connection identifiers (CIDs) in the
	of any received ICMP message).		quoted packet of any received ICMP message).
	7. Acknowledgements		7. Acknowledgments
	This work was partially funded by the European Union's Horizon 2020		This work was partially funded by the European Union's Horizon 2020
	research and innovation programme under grant agreement No. 644334		research and innovation programme under grant agreement No. 644334
	(NEAT). The views expressed are solely those of the author(s).		(NEAT). The views expressed are solely those of the author(s).
	Thanks to all that have commented or contributed, the TSVWG and QUIC		Thanks to all that have commented or contributed, the TSVWG and QUIC
	working groups, and Mathew Calder and Julius Flohr for providing		working groups, and Mathew Calder and Julius Flohr for providing
	early implementations.		early implementations.
	8. IANA Considerations		8. IANA Considerations
	skipping to change at page 36, line 41 ¶		skipping to change at page 37, line 43 ¶
	hole data by indicating a size larger than supported by the path.		hole data by indicating a size larger than supported by the path.
	Parallel forwarding paths SHOULD be considered. Section 5.4		Parallel forwarding paths SHOULD be considered. Section 5.4
	identifies the need for robustness in the method because the path		identifies the need for robustness in the method because the path
	information might be inconsistent.		information might be inconsistent.
	A node performing DPLPMTUD could experience conflicting information		A node performing DPLPMTUD could experience conflicting information
	about the size of supported probe packets. This could occur when		about the size of supported probe packets. This could occur when
	there are multiple paths are concurrently in use and these exhibit a		there are multiple paths are concurrently in use and these exhibit a
	different PMTU. If not considered, this could result in packets not		different PMTU. If not considered, this could result in packets not
	being delivered (black holed) when the PLPMTU is larger than the		being delivered (black holed) when the PLPMTU results in a packet
	smallest actual PMTU.		larger than the smallest actual PMTU.
	DPLPMTUD methods can introduce padding data to inflate the length of		DPLPMTUD methods can introduce padding data to inflate the length of
	the datagram to the total size required for a probe packet. The		the datagram to the total size required for a probe packet. The
	total size of a probe packet includes all headers and padding added		total size of a probe packet includes all headers and padding added
	to the payload data being sent (e.g., including security-related		to the payload data being sent (e.g., including security-related
	fields such as an AEAD tag and TLS record layer padding). The value		fields such as an AEAD tag and TLS record layer padding). The value
	of the padding data does not influence the DPLPMTUD search algorithm,		of the padding data does not influence the DPLPMTUD search algorithm,
	and therefore needs to be set consistent with the policy of the PL.		and therefore needs to be set consistent with the policy of the PL.
	If a PL can make use of cryptographic confidentiality or data-		If a PL can make use of cryptographic confidentiality or data-
	integrity mechanisms, then adding anything (e.g., padding) for		integrity mechanisms, then the design ought to avoid adding anything
	DPLPMTUD that is not protected by those cryptographic mechanisms is		(e.g., padding) to DPLPMTUD probe packets that is not also protected
	an anti-pattern to be avoided.		by those cryptographic mechanisms.
	10. References		10. References
	10.1. Normative References		10.1. Normative References
	[I-D.ietf-quic-transport]		[I-D.ietf-quic-transport]
	Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed		Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
	and Secure Transport", Work in Progress, Internet-Draft,		and Secure Transport", Work in Progress, Internet-Draft,
	draft-ietf-quic-transport-27, 21 February 2020,		draft-ietf-quic-transport-27, 21 February 2020,
	<http://www.ietf.org/internet-drafts/draft-ietf-quic-		<http://www.ietf.org/internet-drafts/draft-ietf-quic-
	skipping to change at page 42, line 51 ¶		skipping to change at page 44, line 4 ¶
	* Removed section on DPLPMTUD with UDP Options.		* Removed section on DPLPMTUD with UDP Options.
	* Shortened the description of phases.		* Shortened the description of phases.
	Working group draft -09:		Working group draft -09:
	* Remove final mention of UDP Options		* Remove final mention of UDP Options
	* Add Initial Connectivity sections to each PL		* Add Initial Connectivity sections to each PL
	* Add to disable outgoing pmtu enforcement of packets		* Add to disable outgoing pmtu enforcement of packets
	Working group draft -10:		Working group draft -10:
	* Address comments from Lars Eggert		* Address comments from Lars Eggert
	* Reinforce that PROBE_COUNT is successive attempts to probe for any		* Reinforce that PROBE_COUNT is successive attempts to probe for any
	size		size
	* Redefine MAx_PROBES to 3		* Redefine MAX_PROBES to 3
	* Address PTB_SIZE of 0 or less that MIN_PMTU		* Address PTB_SIZE of 0 or less that MIN_PLPMTU
	Working group draft -11:		Working group draft -11:
	* Restore a sentence removed in previous rev		* Restore a sentence removed in previous rev
	* De-acronymise QUIC		* De-acronymise QUIC
	* Address some nits		* Address some nits
	Working group draft -12:		Working group draft -12:
	* Add TSVWG, QUIC and implementers to acknowledgements		* Add TSVWG, QUIC and implementers to acknowledgments
	* Shorten a diagram line.		* Shorten a diagram line.
	* Address nits from Julius and Wes.		* Address nits from Julius and Wes.
	* Be clearer when talking about IP layer caches		* Be clearer when talking about IP layer caches
			Working group draft -13, -14:
			* Updated after WGLC.
			Working group draft -15:
			* Updated after AD evaluation and prepared for IETF-LC.
			Working group draft -16:
			* Updated text after SECDIR review.
			Working group draft -17:
			* Updated text after GENART and IETF-LC.
			* Renamed BASE_MTU to BASE_PLPMTU, and MIN and MAX PMTU to PLPMTU
			(because these are about a base for the PLPMTU), and ensured
			consistent separation of PMTU and PLPMTU.
			* Adopted US-style English throughout.
	Authors' Addresses		Authors' Addresses
	Godred Fairhurst		Godred Fairhurst
	University of Aberdeen		University of Aberdeen
	School of Engineering		School of Engineering
	Fraser Noble Building		Fraser Noble Building
	Aberdeen		Aberdeen
	AB24 3UE		AB24 3UE
	United Kingdom		United Kingdom
End of changes. 108 change blocks.
	296 lines changed or deleted		352 lines changed or added
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