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Path MTU discovery (RFC1191)

IP.com Disclosure Number: IPCOM000002004D
Original Publication Date: 1990-Nov-01
Included in the Prior Art Database: 2000-Sep-12
Document File: 17 page(s) / 45K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

J.C. Mogul: AUTHOR [+2]

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.

This text was extracted from a ASCII Text document.
This is the abbreviated version, containing approximately 7% of the total text.

Network Working Group J. Mogul

Request for Comments: 1191 DECWRL

Obsoletes: RFC 1063 S. Deering

Stanford University

November 1990

Path MTU Discovery

Status of this Memo

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.

Table of Contents

Status of this Memo 1

Abstract 2

Acknowledgements 2

1. Introduction 2

2. Protocol overview 3

3. Host specification 4

3.1. TCP MSS Option 5

4. Router specification 6

5. Host processing of old-style messages 7

6. Host implementation 8

6.1. Layering 9

6.2. Storing PMTU information 10

6.3. Purging stale PMTU information 11

6.4. TCP layer actions 13

6.5. Issues for other transport protocols 14

6.6. Management interface 15

7. Likely values for Path MTUs 15

7.1. A better way to detect PMTU increases 16

8. Security considerations 18

References 18

Authors' Addresses 19

List of Tables

Table 7-1: Common MTUs in the Internet 17

RFC 1191 Path MTU Discovery November 1990

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 prac...