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Maximum Transmission Unit Signalling Extensions for the Label Distribution Protocol (RFC3988)

IP.com Disclosure Number: IPCOM000039275D
Original Publication Date: 2005-Jan-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 10 page(s) / 19K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

B. Black: AUTHOR [+2]

Abstract

Proper functioning of RFC 1191 path Maximum Transmission Unit (MTU) discovery requires that IP routers have knowledge of the MTU for each link to which they are connected. As currently specified, the Label Distribution Protocol (LDP) does not have the ability to signal the MTU for a Label Switched Path (LSP) to the ingress Label Switching Router (LSR). In the absence of this functionality, the MTU for each LSP must be statically configured by network operators or by equivalent off-line mechanisms.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 14% of the total text.

Network Working Group                                           B. Black

Request for Comments: 3988                               Layer8 Networks

Category: Experimental                                       K. Kompella

                                                        Juniper Networks

                                                            January 2005

            Maximum Transmission Unit Signalling Extensions

                  for the Label Distribution Protocol

Status of This Memo

   This memo defines an Experimental Protocol for the Internet

   community.  It does not specify an Internet standard of any kind.

   Discussion and suggestions for improvement are requested.

   Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   Proper functioning of RFC 1191 path Maximum Transmission Unit (MTU)

   discovery requires that IP routers have knowledge of the MTU for each

   link to which they are connected.  As currently specified, the Label

   Distribution Protocol (LDP) does not have the ability to signal the

   MTU for a Label Switched Path (LSP) to the ingress Label Switching

   Router (LSR).  In the absence of this functionality, the MTU for each

   LSP must be statically configured by network operators or by

   equivalent off-line mechanisms.

   This document specifies experimental extensions to LDP in support of

   LSP MTU discovery.

1.  Introduction

   As currently specified in [2], the LDP protocol for MPLS does not

   support signalling of the MTU for LSPs to ingress LSRs.  This

   functionality is essential to the proper functioning of RFC 1191 path

   MTU detection [3].  Without knowledge of the MTU for an LSP, edge

   LSRs may transmit packets along that LSP which are, according to [4],

   too big.  These packets may be silently discarded by LSRs along the

   LSP, effectively preventing communication between certain end hosts.

Black & Kompella              Experimental                      [Page 1]

RFC 3988           MTU Signalling Extensions for LDP        January 2005

   The solution proposed in this document enables automatic

   determination of the MTU for an LSP by adding a Type-Length-Value

   triplet (TLV) to carry MTU information for a Forwarding Equivalence

   Class (FEC) between adjacent LSRs in LDP Label Mapping messages.

   This information is sufficient for a set of LSRs along the path

   followed by an LSP to discover either the exact MTU for that LSP, or

   an approximation that is no worse than could be generated with local

   information on the ingress LSR.

1.1.  Conventions Used in...