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).
AbstractThis 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. 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
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.
RFC2119]. Figure 1 contains sample output from an enhanced TRACEROUTE implementation. > traceroute 192.0.2.1 traceroute to 192.0.2.1 (192.0.2.1), 30 hops max, 40 byte packets 1 192.0.2.13 (192.0.2.13) 0.661 ms 0.618 ms 0.579 ms 2 192.0.2.9 (192.0.2.9) 0.861 ms 0.718 ms 0.679 ms MPLS Label=100048 Exp=0 TTL=1 S=1 3 192.0.2.5 (192.0.2.5) 0.822 ms 0.731 ms 0.708 ms MPLS Label=100016 Exp=0 TTL=1 S=1 4 192.0.2.1 (192.0.2.1) 0.961 ms 8.676 ms 0.875 ms Figure 1: Enhanced TRACEROUTE Sample Output Section 2.3 of [RFC3032] defines this relationship. The current memo does not define encapsulation-specific TTL (Time to Live) manipulation procedures. It defers to Section 5.4 of RFC 3034 [RFC3034] and Section 10 of [RFC3035] in this matter.
When encapsulation-specific TTL manipulation procedures defeat the basic TRACEROUTE mechanism, they will also defeat enhanced TRACEROUTE implementations. Figure 2 depicts the MPLS Label Stack Object. It must be preceded by an ICMP Extension Structure Header and an ICMP Object Header. Both are defined in [RFC4884]. In the object payload, octets 0-3 depict the first member of the MPLS label stack. Each remaining member of the MPLS label stack is represented by another 4 octets that share the same format. Class-Num = 1, MPLS Label Stack Class C-Type = 1, Incoming MPLS Label Stack Length = 4 + 4 * (number of MPLS LSEs) 0 1 2 3 +-------------+-------------+-------------+-------------+ | Label |EXP |S| TTL | +-------------+-------------+-------------+-------------+ | | | // Remaining MPLS Label Stack Entries // | | | +-------------+-------------+-------------+-------------+ Figure 2: MPLS Label Stack Object Label: 20 bits Exp: Experimental Use, 3 bits S: Bottom of Stack, 1 bit TTL: Time to Live, 8 bits
[RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, RFC 792, September 1981. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 2434, October 1998. [RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack Encoding", RFC 3032, January 2001. [RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification", RFC 4443, March 2006. [RFC4884] Bonica, R., Gan, D., Tappan, D., and C. Pignataro, "Extended ICMP to Support Multi-Part Messages", RFC 4884, April 2007. [RFC3034] Conta, A., Doolan, P., and A. Malis, "Use of Label Switching on Frame Relay Networks Specification", RFC 3034, January 2001. [RFC3035] Davie, B., Lawrence, J., McCloghrie, K., Rosen, E., Swallow, G., Rekhter, Y., and P. Doolan, "MPLS using LDP and ATM VC Switching", RFC 3035, January 2001. [RFC3443] Agarwal, P. and B. Akyol, "Time To Live (TTL) Processing in Multi-Protocol Label Switching (MPLS) Networks", RFC 3443, January 2003.
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