Network Working Group R. Bonica
Request for Comments: 4950 Juniper Networks
Category: Standards Track D. Gan
D. Tappan
Consultant
C. Pignataro
Cisco Systems, Inc.
August 2007
ICMP Extensions for Multiprotocol Label Switching
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 memo defines an extension object that can be appended to
selected multi-part ICMP messages. This extension permits Label
Switching Routers to append MPLS information to ICMP messages, and
has already been widely deployed.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions Used in This Document . . . . . . . . . . . . . . . 3
3. Application to TRACEROUTE . . . . . . . . . . . . . . . . . . . 3
4. Disclaimer . . . . . . . . . . . . . . . . . . . . . . . . . . 3
5. MPLS Label Stack Object . . . . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . . 6
Bonica, et al. Standards Track [Page 1]
RFC 4950 ICMP MPLS August 2007
1. Introduction
IP routers use the Internet Control Message Protocol, ICMPv4
[RFC0792] and ICMPv6 [RFC4443], to convey control information to
source hosts. Network operators use this information to diagnose
routing problems.
When a router receives an undeliverable IP datagram, it can send an
ICMP message to the host that originated the datagram. The ICMP
message indicates why the datagram could not be delivered. It also
contains the IP header and leading payload octets of the "original
datagram" to which the ICMP message is a response.
MPLS Label Switching Routers (LSR) also use ICMP to convey control
information to source hosts. Section 2.3 of [RFC3032] describes the
interaction between MPLS and ICMP, and Sections 2.4 and 3 of
[RFC3032] provide applications of that interaction.
When an LSR receives an undeliverable MPLS-encapsulated datagram, it
removes the entire MPLS label stack, exposing the previously
encapsulated IP datagram. The LSR then submits the IP datagram to an
error processing module. Error processing can include ICMP message
generation.
The ICMP message indicates why the original datagram could not be
delivered. It also contains the IP header and leading octets of the
original datagram.
The ICMP message, however, contains no information regarding the MPLS
label stack that encapsulated the original datagram when it arrived
at the LSR. This omission is significant because the LSR would have
forwarded the original datagram based upon information contained by
the MPLS label stack.
This memo defines an ICMP extension object that permits an LSR to
append MPLS information to ICMP messages. Selected ICMP messages
SHOULD include the MPLS label stack, as it arrived at the router that
is sending the ICMP message. The ICMP message MUST also include the
IP header and leading payload octets of the original datagram.
The ICMP extensions defined in this document must be preceded by an
ICMP Extension Structure Header and an ICMP Object Header. Both are
defined in [RFC4884].
The ICMP extension defined in this document is equally applicable to
ICMPv4 [RFC0792] and ICMPv6 [RFC4443]. Throughout this document,
unless otherwise specified, the acronym ICMP refers to multi-part
ICMP messages, encompassing both ICMPv4 and ICMPv6.
Bonica, et al. Standards Track [Page 2]
RFC 4950 ICMP MPLS August 2007
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