Packetization Layer Path MTU Discovery
RFC 4821
Document | Type |
RFC - Proposed Standard
(March 2007; No errata)
Updated by RFC 8899
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|
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Authors | Matt Mathis , John Heffner | ||
Last updated | 2020-07-29 | ||
Stream | IETF | ||
Formats | plain text html pdf htmlized bibtex | ||
Reviews | |||
Stream | WG state | (None) | |
Document shepherd | No shepherd assigned | ||
IESG | IESG state | RFC 4821 (Proposed Standard) | |
Action Holders |
(None)
|
||
Consensus Boilerplate | Unknown | ||
Telechat date | |||
Responsible AD | Lars Eggert | ||
Send notices to | (None) |
Network Working Group M. Mathis Request for Comments: 4821 J. Heffner Category: Standards Track PSC March 2007 Packetization Layer Path MTU Discovery Status of This Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The IETF Trust (2007). Abstract This document describes a robust method for Path MTU Discovery (PMTUD) 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. Mathis & Heffner Standards Track [Page 1] RFC 4821 Packetization Layer Path MTU Discovery March 2007 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 4. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 9 5. Layering . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 5.1. Accounting for Header Sizes . . . . . . . . . . . . . . . 10 5.2. Storing PMTU Information . . . . . . . . . . . . . . . . . 11 5.3. Accounting for IPsec . . . . . . . . . . . . . . . . . . . 12 5.4. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 12 6. Common Packetization Properties . . . . . . . . . . . . . . . 13 6.1. Mechanism to Detect Loss . . . . . . . . . . . . . . . . . 13 6.2. Generating Probes . . . . . . . . . . . . . . . . . . . . 13 7. The Probing Method . . . . . . . . . . . . . . . . . . . . . . 14 7.1. Packet Size Ranges . . . . . . . . . . . . . . . . . . . . 14 7.2. Selecting Initial Values . . . . . . . . . . . . . . . . . 16 7.3. Selecting Probe Size . . . . . . . . . . . . . . . . . . . 17 7.4. Probing Preconditions . . . . . . . . . . . . . . . . . . 18 7.5. Conducting a Probe . . . . . . . . . . . . . . . . . . . . 18 7.6. Response to Probe Results . . . . . . . . . . . . . . . . 19 7.6.1. Probe Success . . . . . . . . . . . . . . . . . . . . 19 7.6.2. Probe Failure . . . . . . . . . . . . . . . . . . . . 19 7.6.3. Probe Timeout Failure . . . . . . . . . . . . . . . . 20 7.6.4. Probe Inconclusive . . . . . . . . . . . . . . . . . . 20 7.7. Full-Stop Timeout . . . . . . . . . . . . . . . . . . . . 20 7.8. MTU Verification . . . . . . . . . . . . . . . . . . . . . 21 8. Host Fragmentation . . . . . . . . . . . . . . . . . . . . . . 22 9. Application Probing . . . . . . . . . . . . . . . . . . . . . 23 10. Specific Packetization Layers . . . . . . . . . . . . . . . . 23 10.1. Probing Method Using TCP . . . . . . . . . . . . . . . . . 23 10.2. Probing Method Using SCTP . . . . . . . . . . . . . . . . 25 10.3. Probing Method for IP Fragmentation . . . . . . . . . . . 26 10.4. Probing Method Using Applications . . . . . . . . . . . . 27 11. Security Considerations . . . . . . . . . . . . . . . . . . . 28 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 28 12.1. Normative References . . . . . . . . . . . . . . . . . . . 28 12.2. Informative References . . . . . . . . . . . . . . . . . . 29 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 31 Mathis & Heffner Standards Track [Page 2] RFC 4821 Packetization Layer Path MTU Discovery March 2007 1. Introduction This document describes a method for Packetization Layer Path MTU Discovery (PLPMTUD), which is an extension to existing Path MTU Discovery methods described in [RFC1191] and [RFC1981]. In the absence of ICMP messages, the proper MTU is determined by starting with small packets and probing with successively larger packets. The bulk of the algorithm is implemented above IP, in the transport layer (e.g., TCP) or other "Packetization Protocol" that is responsible for determining packet boundaries. This document does not update RFC 1191 or RFC 1981; however, since it supports correct operation without ICMP, it implicitly relaxes some of the requirements for the algorithms specified in those documents. The methods described in this document rely on features of existingShow full document text