Packetization Layer Path MTU Discovery
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From: The IESG <firstname.lastname@example.org> To: IETF-Announce <email@example.com> Cc: Internet Architecture Board <firstname.lastname@example.org>, RFC Editor <email@example.com>, pmtud mailing list <firstname.lastname@example.org>, pmtud chair <email@example.com> Subject: Protocol Action: 'Packetization Layer Path MTU Discovery' to Proposed Standard The IESG has approved the following document: - 'Packetization Layer Path MTU Discovery ' <draft-ietf-pmtud-method-12.txt> as a Proposed Standard This document is the product of the Path MTU Discovery Working Group. The IESG contact persons are Lars Eggert and Magnus Westerlund. A URL of this Internet-Draft is: http://www.ietf.org/internet-drafts/draft-ietf-pmtud-method-12.txt
Technical Summary This document describes a robust method for Path MTU Discovery ("Packetization Layer Path MTU Discovery" or PLPMTUD) that relies on TCP or some other Packetization Layer to probe an Internet path with progressively larger packets. This method is described as an extension to RFC 1191 and RFC 1981, which specify ICMP based Path MTU Discovery for IP versions 4 and 6, respectively. The general strategy of the new algorithm is to start with a small MTU and search upward, testing successively larger MTUs by probing with single packets. If a probe is successfully delivered then the MTU can be raised. If the probe is lost, it is treated as an MTU limitation and not as a congestion signal. PLPMTUD introduces some flexibility in the implementation of classical Path MTU discovery. If can be configured to perform just ICMP black hole recovery to increase the robustness of classical Path MTU Discovery, or at the other extreme, all ICMP processing can be disabled and PLPMTUD can completely replace classical Path MTU Discovery. Working Group Summary The working group feels that an update to path MTU discovery is needed to rectify problems with current "classical" path MTU discovery that occur in today's network deployments (which result in Path MTU "black holes", and the failure of not only the algorithm but often the entire connection). The document has had considerable review by the working group over its eight revisions, and the comments have been incorporated in the current draft. Reviewers have had background in TCP, SCTP, DCCP, the use of tunnels (ipsec and other) and IPv6. The WGLC version has had four careful reviews that only revealed nits and clarifications that are fixed in this version. Protocol Quality The current protocol has one implementation in Linux, by a co-author, and another independent implementation in a user-space transport protocol. Previous versions have had implementation in Linux, NetBSD, and FreeBSD, by different people, resulting in comments that contributed to document changes. Other operating systems vendors and tunnel vendors have reviewed the document. Matt Zekauskas (firstname.lastname@example.org) acted as Document Shepherd. Lars Eggert (email@example.com) has reviewed this document for the IESG.