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Traditional (RFC1191) Path MTU Discovery
rfc1191 121340970 describes a method for a sender to detect the Path MTU to a given receiver. (rfc1981 121340970 describes the equivalent for IPv6.) The method works as follows:
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This method is widely implemented, but is not robust in today's Internet because it relies on ICMP packets sent by routers along the path. Such packets are often suppressed either at the router that should generate them (to protect its resources) or on the way back to the source, because of firewalls and other packet filters or rate limitations. These problems are described in rfc2923 121340970. When packets are lost due to MTU issues without any ICMP "Too Big" message, this is sometimes called a (MTU) black hole. Some operating systems have added heuristics to detect such black holes and work around them. Workarounds can include lowering the MTU estimate or disabling PMTUD for certain destinations.
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- RFC 4821, Packetization Layer Path MTU Discovery, M. Mathis, J. Heffner, March 2007.
- RFC 1191, Path MTU discovery, Mogul, J. and S. Deering, November 1990.
- RFC 1981, Path MTU Discovery for IP version 6, McCann, J., Deering, S., and J. Mogul, August 1996.
- draft-ietf-6man-rfc1981bis-06, Path MTU Discovery for IP version 6, Jack McCann, Stephen E. Deering, Jeffrey Mogul, Robert M. Hinden, April 2017
- RFC 2923, TCP Problems with Path MTU Discovery, K. Lahey, September 2000
- RFC 3128, Protection Against a Variant of the Tiny Fragment Attack (RFC 1858), Miller, I., June 2001.
- RFC 4459, MTU and Fragmentation Issues with In-the-Network Tunneling, P. Savola, February 2006.
- draft-saum-nvo3-pmtud-over-vxlan-05, PMTUD Over Vxlan, Saumya Dikshit, A Sujeet Nayak, June 2017
- Measuring the Evolution of Transport Protocols in the Internet, A. Medina, M. Allman, and S. Floyd, April 2005.
- PMTU (Path MTU) Discovery - Some servers are unusable for many internet users, an article about problems with Path MTU Discovery and their effects.
- Practical hints from Cisco for working around PMTUD issues, for Windows, Solaris, and other systems
- IP Fragmentation and PMTUD, Cisco White Paper
- draft-ietf-tsvwg-datagram-plpmtud-07, Packetization Layer Path MTU Discovery for Datagram Transports, Godred Fairhurst, Tom Jones, Michael Tuexen, Irene Ruengeler, Timo Voelker, February 2019
- draft-spiriyath-ipsecme-dynamic-ipsec-pmtu-01, Packetization Layer Path Maximum Transmission Unit Discovery (PLPMTUD)For IPsec Tunnels, Shibu Piriyath, Umesh Mangla, Nagavenkata Suresh Melam, Ron Bonica, February 2018
draft-troan-6man-pmtu-solution-space-00, Path MTU discovery solution space, Ole Troan, September 2018
- draft-fairhurst-tsvwg-udp-options-dplpmtud-00, Datagram PLPMTUD for UDP Options, Godred Fairhurst, Tom Jones, April 2019
Implementations
- for Linux 2.6 - integrated in mainstream kernel as of 2.6.17. However, it is disabled by default (see net.ipv4.tcp_mtu_probing sysctl)
- for NetBSD
-- HankNussbacher - 2005-07-03
– SimonLeinen - 2006-07-19 - 2019-0204-1827