A new IETF working group has been proposed in the Transport Area. The IESG has not made any determination as yet. The following description was submitted, ans is provided for informational purposes only: Path Maximum Transmission Unit Discovery (pmutd) ------------------------------------------------ Current Status: Proposed Working Group Chair(s): Matt Mathis <mathis@psc.edu> TBD Transport Area Directors(s): Allison Mankin <mankin@psg.com> Jon Peterson <jon.peterson@neustar.biz> Transport 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.
