rfc9268v3.txt		rfc9268.txt
	skipping to change at line 213 ¶		skipping to change at line 213 ¶
	mean that the Min-PMTU value does not account for all links along a		mean that the Min-PMTU value does not account for all links along a
	path.		path.
	2. Motivation and Problem Solved		2. Motivation and Problem Solved
	The current state of Path MTU Discovery on the Internet is		The current state of Path MTU Discovery on the Internet is
	problematic. The mechanisms defined in [RFC8201] are known to not		problematic. The mechanisms defined in [RFC8201] are known to not
	work well in all environments. It fails to work in various cases,		work well in all environments. It fails to work in various cases,
	including when nodes in the middle of the network do not send ICMPv6		including when nodes in the middle of the network do not send ICMPv6
	PTB messages or rate-limited ICMPv6 messages or do not have a return		PTB messages or rate-limited ICMPv6 messages or do not have a return
	path to the source host.		path to the source host. This results in many transport-layer
			connections being configured to use smaller packets (e.g., 1280
	This results in many transport-layer connections being configured to		bytes) by default and makes it difficult to take advantage of paths
	use smaller packets (e.g., 1280 bytes) by default and makes it		with a larger PMTU where they do exist. Applications that send large
	difficult to take advantage of paths with a larger PMTU where they do		packets are forced to use IPv6 fragmentation [RFC8200], which can
	exist. Applications that send large packets are forced to use IPv6		reduce the reliability of Internet communication [RFC8900].
	fragmentation [RFC8200], which can reduce the reliability of Internet
	communication [RFC8900].
	Encapsulations and network-layer tunnels further reduce the payload		Encapsulations and network-layer tunnels further reduce the payload
	size available for a transport protocol to use. Also, some use cases		size available for a transport protocol to use. Also, some use cases
	increase packet overhead, for example, Network Virtualization Using		increase packet overhead, for example, Network Virtualization Using
	Generic Routing Encapsulation (NVGRE) [RFC7637] encapsulates Layer 2		Generic Routing Encapsulation (NVGRE) [RFC7637] encapsulates Layer 2
	(L2) packets in an outer IP header and does not allow IP		(L2) packets in an outer IP header and does not allow IP
	fragmentation.		fragmentation.
	Sending larger packets can improve host performance, e.g., avoiding		Sending larger packets can improve host performance, e.g., avoiding
	limits to packet processing by the packet rate. An example of this		limits to packet processing by the packet rate. An example of this
	skipping to change at line 304 ¶		skipping to change at line 302 ¶
	Option Type (see Section 4.2 of [RFC8200]):		Option Type (see Section 4.2 of [RFC8200]):
	BB 00 Skip over this Option and continue processing.		BB 00 Skip over this Option and continue processing.
	C 1 Option Data can change en route to the packet's final		C 1 Option Data can change en route to the packet's final
	destination.		destination.
	TTTTT 10000 Option Type assigned from IANA [IANA-HBH].		TTTTT 10000 Option Type assigned from IANA [IANA-HBH].
	Length: 4 The size of the value field in Option Data		Length: 4 The size of the value field in Option Data
	field supports PMTU values from 0 to 65,534 octets, the		field supports PMTU values from 0 to 65,534
	maximum size represented by the Path MTU Option.		octets, the maximum size represented by the
			Path MTU Option.
	Min-PMTU: n 16-bits. The minimum MTU recorded along the path		Min-PMTU: n 16-bits. The minimum MTU recorded along the path
	in octets, reflecting the smallest link MTU that		in octets, reflecting the smallest link MTU that
	the packet experienced along the path.		the packet experienced along the path.
	A value less than the IPv6 minimum link		A value less than the IPv6 minimum link
	MTU [RFC8200] MUST be ignored.		MTU [RFC8200] MUST be ignored.
	Rtn-PMTU: n 15-bits. The returned Path MTU field, carrying the 15		Rtn-PMTU: n 15-bits. The returned Path MTU field, carrying the 15
	most significant bits of the latest received Min-PMTU		most significant bits of the latest received Min-PMTU
	field for the forward path. The value zero means that		field for the forward path. The value zero means that
	skipping to change at line 493 ¶		skipping to change at line 492 ¶
	* The MinPMTU HBH Option can be used with ICMPv6 [RFC4443]. This		* The MinPMTU HBH Option can be used with ICMPv6 [RFC4443]. This
	requires a response from the remote node and therefore is		requires a response from the remote node and therefore is
	restricted to use with ICMPv6 echo messages. The MinPMTU HBH		restricted to use with ICMPv6 echo messages. The MinPMTU HBH
	Option could provide additional information about the PMTU that		Option could provide additional information about the PMTU that
	might be supported by a path. This could be used as a diagnostic		might be supported by a path. This could be used as a diagnostic
	tool to measure the PMTU of a path. As with other uses, the		tool to measure the PMTU of a path. As with other uses, the
	actual supported PMTU is only confirmed after receiving a response		actual supported PMTU is only confirmed after receiving a response
	to a subsequent probe of the PMTU size.		to a subsequent probe of the PMTU size.
	* A datagram transport can utilize Datagram Packetization Layer PMTU		* A datagram transport can utilize DPLPMTUD [RFC8899]. For example,
	Discovery (DPLPMTUD) [RFC8899]. For example, QUIC (see		QUIC (see Section 14.3 of [RFC9000]) can use DPLPMTUD to determine
	Section 14.3 of [RFC9000]) can use DPLPMTUD to determine whether		whether the path to a destination will support a desired maximum
	the path to a destination will support a desired maximum datagram		datagram size. When using the IPv6 MinPMTU HBH Option, the Option
	size. When using the IPv6 MinPMTU HBH Option, the Option could be		could be added to an additional QUIC PMTU probe that is of minimal
	added to an additional QUIC PMTU probe that is of minimal size (or		size (or one no larger than the currently supported PMTU size).
	one no larger than the currently supported PMTU size). Once the		Once the return Path MTU value in the MinPMTU HBH Option has been
	return Path MTU value in the MinPMTU HBH Option has been learned,		learned, DPLPMTUD can be triggered to test for a larger PLPMTU
	DPLPMTUD can be triggered to test for a larger PLPMTU using an		using an appropriately sized PLPMTU probe packet (see
	appropriately sized PLPMTU probe packet (see Section 5.3.1 of		Section 5.3.1 of [RFC8899]).
	[RFC8899]).
	* The use of this Option with DNS and DNSSEC over UDP is expected to		* The use of this Option with DNS and DNSSEC over UDP is expected to
	work for paths where the PMTU is symmetric. The DNS server will		work for paths where the PMTU is symmetric. The DNS server will
	learn the PMTU from the DNS query messages. If the Rtn-PMTU value		learn the PMTU from the DNS query messages. If the Rtn-PMTU value
	is smaller, then a large DNSSEC response might be dropped and the		is smaller, then a large DNSSEC response might be dropped and the
	known problems with PMTUD will then occur. DNS and DNSSEC over		known problems with PMTUD will then occur. DNS and DNSSEC over
	transport protocols that can carry the PMTU ought to work.		transport protocols that can carry the PMTU ought to work.
	* This method also can be used with anycast to discover the PMTU of		* This method also can be used with anycast to discover the PMTU of
	the path, but the use needs to be aware that the anycast binding		the path, but the use needs to be aware that the anycast binding
	skipping to change at line 988 ¶		skipping to change at line 986 ¶
	----Probe size d ---------------------------------------->		----Probe size d ---------------------------------------->
	<---------------------------------- ACK of probe --------		<---------------------------------- ACK of probe --------
	----Packets of data size d ------------------------------>		----Packets of data size d ------------------------------>
	<---------------------------------- ACK of probe --------		<---------------------------------- ACK of probe --------
	...		...
	----Probe size e --------------X		----Probe size e --------------X
	X----ICMPv6 PTB d' ----|		X----ICMPv6 PTB d' ----|
	----Packets of data size d ------------------------------>		----Packets of data size d ------------------------------>
	----Probe size e --------------X (again)		----Probe size e --------------X (again)
	X----ICMPv6 PTB d' ----|		X----ICMPv6 PTB d' ----|
	----Packets of data size d -------------------------------		----Packets of data size d ------------------------------>
	...		...
	etc. until MaxProbes are unsuccessful and search phase completes.		etc. until MaxProbes are unsuccessful and search phase completes.
	----Packets of data size d ------------------------------>		----Packets of data size d ------------------------------>
	Figure 3		Figure 3
	The second example considers DPLPMTUD with the MinPMTU HBH Option set		The second example considers DPLPMTUD with the MinPMTU HBH Option set
	on a connectivity probe packet.		on a connectivity probe packet.
	The IPv6 Option is sent end to end, and the Min-PMTU is updated by a		The IPv6 Option is sent end to end, and the Min-PMTU is updated by a
	skipping to change at line 1033 ¶		skipping to change at line 1031 ¶
	connectivity probe packet is dropped.		connectivity probe packet is dropped.
	In this case, the packet with the MinPMTU HBH Option is not received.		In this case, the packet with the MinPMTU HBH Option is not received.
	DPLPMTUD searches using probe packets of increasing size, increasing		DPLPMTUD searches using probe packets of increasing size, increasing
	the PLPMTU when the probes are confirmed. An ICMPv6 PTB message is		the PLPMTU when the probes are confirmed. An ICMPv6 PTB message is
	received when the probed size exceeds the actual PMTU, indicating a		received when the probed size exceeds the actual PMTU, indicating a
	PTB_SIZE of d'. DPLPMTUD immediately sends a probe packet of the		PTB_SIZE of d'. DPLPMTUD immediately sends a probe packet of the
	target size d'. If the probe packet is confirmed for the path, the		target size d'. If the probe packet is confirmed for the path, the
	PLPMTU is updated, allowing the source to use data packets up to size		PLPMTU is updated, allowing the source to use data packets up to size
	d'. If the ICMPv6 PTB message is not received, the DPLPMTU will be		d'. If the ICMPv6 PTB message is not received, the DPLPMTU will be
	the last confirmed probe size d.		the last confirmed probe size, which is d.
	----Packets of data size a ------------------------------->		----Packets of data size a ------------------------------->
	----Connectivity probe with MinPMTU --------X		----Connectivity probe with MinPMTU --------X
	----Packets of data size a ------------------------------->		----Packets of data size a ------------------------------->
	----Probe size b ----------------------------------------->		----Probe size b ----------------------------------------->
	<---------------------------------- ACK of probe --------		<---------------------------------- ACK of probe --------
	----Packets of data size b ------------------------------->		----Packets of data size b ------------------------------->
	----Probe size c ----------------------------------------->		----Probe size c ----------------------------------------->
	<---------------------------------- ACK of probe --------		<---------------------------------- ACK of probe --------
	----Packets of data size c ------------------------------->		----Packets of data size c ------------------------------->
End of changes. 5 change blocks.
	23 lines changed or deleted		21 lines changed or added
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