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Internal WG Review: Path Maximum Transmission Unit Discovery (pmutd)
A new IETF working group is being considered in the Transport Area.
The draft charter for this working group is provided below for your review and comment.
Path Maximum Transmission Unit Discovery (pmutd)
Chair(s):
Matt Mathis <mathis@psc.edu>
TBD
Transport Area Directors(s):
Allison Mankin <mankin@psg.com>
Jon Peterson <jon.peterson@neustar.biz>
Area Advisor:
Allison Mankin <mankin@psg.com>
Mailing List (temporary):
General Discussion: mtu@psc.edu
Subscribe: majordomo@psc.edu with "subscribe mtu" in the body
Archive: http://www.psc.edu/~mathis/MTU/mbox.txt
(This is to be moved to the IETF as soon as chartered).
Description of Working Group:
The goal of the PMTUD working group is to specify a robust method for
determining the IP Maximum Transmission Unit supported over an
end-to-end path. This new method is expected to update most uses of
RFC1191 and RFC1981, the current standards track protocols for this
purpose. Various weakness in the current methods are documented in
RFC2923, and have proven to be a chronic impediment to the deployment
of new technologies that alter the path MTU, such as tunnels and new
types of link layers.
The proposed new method does not rely on ICMP or other messages from
the network. It finds the proper MTU by starting a connection using
relatively small packets (e.g. TCP segments) and searching upwards by
probing with progressively larger test packets (containing application
data). If a probe packet is successfully delivered, then the path MTU
is raised. The isolated loss of a probe packet (with or without an
ICMP can't fragment message) is treated as an indication of a MTU
limit, and not a congestion indicator.
The working group will specify the method for use in TCP, SCTP, and
will outline what is necessary to support the method in transports
such as DCCP. It will particularly describe the precise conditions
under which lost packets are not treated as congestion indications.
The work will pay particular attention to details that affect
robustness and security.
Path MTU discovery has the potential to interact with many other parts
of the Internet, including all link, transport, encapsulation and
tunnel protocols. Thereforethis working group will particularly
encourage input from a wide cross section of the IETF to help to
maximize the robustness of path MTU discovery in the presence of
pathological behaviors from other components.
Input draft:
Packetization Layer Path MTU Discovery
draft-mathis-plpmtud-00.txt
Goals and Milestones:
Jul 03 Reorganized Internet-Draft. Solicit implementation and field experience.
Dec 03 Update Internet-Draft incorporating implementers experience,
actively solicit input from stakeholders - all communities that might
be affected by changing PMTUD.
Feb 04 Submit completed Internet-draft and a PMTUD MIB draft for
Proposed Standard.