Packetization Layer Path MTU Discovery for Datagram Transports
RFC 8899
Internet Engineering Task Force (IETF) G. Fairhurst
Request for Comments: 8899 T. Jones
Updates: 4821, 4960, 6951, 8085, 8261 University of Aberdeen
Category: Standards Track M. Tüxen
ISSN: 2070-1721 I. Rüngeler
T. Völker
Münster University of Applied Sciences
September 2020
Packetization Layer Path MTU Discovery for Datagram Transports
Abstract
This document specifies Datagram Packetization Layer Path MTU
Discovery (DPLPMTUD). This is a robust method for Path MTU Discovery
(PMTUD) for datagram Packetization Layers (PLs). It allows a PL, or
a datagram application that uses a PL, to discover whether a network
path can support the current size of datagram. This can be used to
detect and reduce the message size when a sender encounters a packet
black hole. It can also probe a network path to discover whether the
maximum packet size can be increased. This provides functionality
for datagram transports that is equivalent to the PLPMTUD
specification for TCP, specified in RFC 4821, which it updates. It
also updates the UDP Usage Guidelines to refer to this method for use
with UDP datagrams and updates SCTP.
The document provides implementation notes for incorporating Datagram
PMTUD into IETF datagram transports or applications that use datagram
transports.
This specification updates RFC 4960, RFC 4821, RFC 6951, RFC 8085,
and RFC 8261.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8899.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction
1.1. Classical Path MTU Discovery
1.2. Packetization Layer Path MTU Discovery
1.3. Path MTU Discovery for Datagram Services
2. Terminology
3. Features Required to Provide Datagram PLPMTUD
4. DPLPMTUD Mechanisms
4.1. PLPMTU Probe Packets
4.2. Confirmation of Probed Packet Size
4.3. Black Hole Detection and Reducing the PLPMTU
4.4. The Maximum Packet Size (MPS)
4.5. Disabling the Effect of PMTUD
4.6. Response to PTB Messages
4.6.1. Validation of PTB Messages
4.6.2. Use of PTB Messages
5. Datagram Packetization Layer PMTUD
5.1. DPLPMTUD Components
5.1.1. Timers
5.1.2. Constants
5.1.3. Variables
5.1.4. Overview of DPLPMTUD Phases
5.2. State Machine
5.3. Search to Increase the PLPMTU
5.3.1. Probing for a Larger PLPMTU
5.3.2. Selection of Probe Sizes
5.3.3. Resilience to Inconsistent Path Information
5.4. Robustness to Inconsistent Paths
6. Specification of Protocol-Specific Methods
6.1. Application Support for DPLPMTUD with UDP or UDP-Lite
6.1.1. Application Request
6.1.2. Application Response
6.1.3. Sending Application Probe Packets
6.1.4. Initial Connectivity
6.1.5. Validating the Path
6.1.6. Handling of PTB Messages
6.2. DPLPMTUD for SCTP
6.2.1. SCTP/IPv4 and SCTP/IPv6
6.2.1.1. Initial Connectivity
6.2.1.2. Sending SCTP Probe Packets
6.2.1.3. Validating the Path with SCTP
6.2.1.4. PTB Message Handling by SCTP
6.2.2. DPLPMTUD for SCTP/UDP
6.2.2.1. Initial Connectivity
6.2.2.2. Sending SCTP/UDP Probe Packets
6.2.2.3. Validating the Path with SCTP/UDP
6.2.2.4. Handling of PTB Messages by SCTP/UDP
6.2.3. DPLPMTUD for SCTP/DTLS
6.2.3.1. Initial Connectivity
6.2.3.2. Sending SCTP/DTLS Probe Packets
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