RFC - 1191

Path MTU Discovery

Original:	ftp://ftp.isi.edu/in-notes/rfc1191.txt
Authors:	J. Mogul [DECWRL], S. Deering [Stanford University]
Date:	November 1990
Category:	Draft Standard

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Obsoletes:
RFC-1063	IP MTU discovery options (Obsoleted by RFC-1191draft)

Referred by:	111 RFC
Refers to:	18 RFC

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Status

This RFC specifies a protocol on the IAB Standards Track for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "IAB Official Protocol Standards" for the standardization state and status of this protocol. Distribution of this memo is unlimited.

Abstract

This memo describes a technique for dynamically discovering the maximum transmission unit (MTU) of an arbitrary internet path. It specifies a small change to the way routers generate one type of ICMP message. For a path that passes through a router that has not been so changed, this technique might not discover the correct Path MTU, but it will always choose a Path MTU as accurate as, and in many cases more accurate than, the Path MTU that would be chosen by current practice.

Acknowledgements

This proposal is a product of the IETF MTU Discovery Working Group.

The mechanism proposed here was first suggested by Geof Cooper [2], who in two short paragraphs set out all the basic ideas that took the Working Group months to reinvent.

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