MPLS Working Group INTERNET DRAFT Ron Bonica July 1999 MCI WorldCom Expires January 2000 Daniel C. Tappan Cisco Systems Der-Hwa Gan Juniper Networks ICMP Extensions for MultiProtocol Label Switching draft-ietf-mpls-icmp-00.txt Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of [RFC-2026]. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet- Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. 1. Abstract The current memo proposes extensions to ICMP that permit LSRs to append MPLS information to ICMP messages. 2. Conventions used in this document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as described in [RFC-2119]. 3. Introduction Routers and destination hosts use the Internet Control Message Protocol (ICMP) [RFC-792] to convey control information to source hosts. Network operators use this information to detect and diagnose Layer 3 routing problems. ICMP Extensions for MPLS July 1999 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 bytes of the undeliverable datagram. MPLS Label Switching Routers (LSRs) also use ICMP to convey control information to source hosts. Sections 2.3 and 2.4 of [ENCODE] describe the interaction between MPLS and ICMP. When an LSR receives an undeliverable MPLS labeled datagram, it removes the entire MPLS label stack, exposing the encapsulated IP datagram. The router then submits the IP datagram to a network- forwarding module for error processing. Error processing can include ICMP message generation. Although the ICMP message contains the non-delivery reason, IP header and leading payload bytes, it contains no information regarding the MPLS label stack that encapsulated the datagram when it arrived at the LSR. The current memo proposes extensions to ICMP that permit LSRs to append MPLS label stack information to the ICMP message body. Hence, ICMP messages regarding undeliverable MPLS encapsulated datagrams 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 bytes of the undeliverable datagram. Network operators will use this information to detect and diagnose MPLS problems. 4. Motivation ICMP extensions defined in the current memo support enhancements to TRACEROUTE. The enhanced TRACEROUTE, like older TRACEROUTE implementations, reports each IP router and LSR that a datagram visits en route to its destination. The enhanced TRACEROUTE differs from older implementations in that it indicates which nodes were visited while traversing a Label Switched Path (LSP). Figure 1 contains sample output from an enhanced TRACEROUTE implementation. ICMP Extensions for MPLS July 1999 >Traceroute 166.45.2.74 traceroute to 166.45.2.74, 30 hops max, 40 byte packets 1 166.45.5.1 1.281 ms 1.103 ms 1.096 ms 2 166.45.4.1 1.281 ms 1.103 ms 1.096 ms mplsLabel1=2001 mplsExpBits1=0 3 166.45.3.1 1.281 ms 1.103 ms 1.096 ms mplsLabel1=2002 mplsExpBits1=0 4 166.45.6.1 1.281 ms 1.103 ms 1.096 ms mplsLabel1=2003 mplsExpBits1=0 5 166.45.2.1 1.281 ms 1.103 ms 1.096 ms 6 166.45.2.74 1.281 ms 1.103 ms 1.096 ms Figure 1. Enhanced TRACEROUTE sample output 5. Disclaimer The current memo does not define the general relationship between ICMP and MPLS. Sections 2.3 and 2.4 of [ENCODE] define this relationship. Specifically, this document defers to [ENCODE] with respect to the following issues: - conditions upon which LSRs emit ICMP messages - handling of ICMP messages bound for hosts that are identified by private addresses The current memo does not define encapsulation specific TTL manipulation procedures. It defers to Section 10 of [MPLSATM] and Section 5.4 of [MPLSFRAME] in this matter. When encapsulation specific TTL manipulation procedures defeat the basic TRACEROUTE mechanism, they will also defeat enhanced TRACEROUTE implementations. 6. Backward Compatibility ICMP extensions proposed in this document MUST be backward compatible with the syntax described in RFC-792. Extensions proposed in this memo MUST NOT change or deprecate any field defined in RFC- 792. ICMP Extensions for MPLS July 1999 7. Formal Syntax This section describes a data structure that can be appended to the following ICMP message types: 1) Destination Unreachable 2) Time Exceeded 3) Parameter Problem 4) Source Quench 5) Redirect The above listed ICMP message types specify a fixed length of 56 bytes. When the data structure defined in this section is appended to an ICMP message, the ICMP _total length_ field MUST equal the data structure length plus 56. The data structure defined in this section consists of a common header followed by object instances. Each object instance consists of an object header plus contents. Currently, only one object class is defined. This object class contains an entire MPLS label stack, formatted exactly as it was when it arrived at the LSR that sends the ICMP message. In the future, additional object classes may be defined. 7.1 Common Header 0 1 2 3 +-------------+-------------+-------------+-------------+ | Vers | (Reserved) | Checksum | +-------------+-------------+-------------+-------------+ The fields in the common header are as follows: Vers: 4 bits ICMP extension version number. This is version 1. Checksum: 16 bits The one's complement of the one's complement sum of the data structure, with the checksum field replaced by zero for the purpose of computing the checksum. An all-zero value means that no checksum was transmitted. If the checksum field contains a value other than described above, bytes 56 and beyond of the ICMP message do not contain the data structure described by this memo. These bytes may ICMP Extensions for MPLS July 1999 contain an extended ICMP payload as described in Section 4.3.2.3 of [RFC-1812]. Reserved: Must be set to 0. 7.2 Object Header Every object consists of one or more 32-bit words with a one-word header, with the following format: 0 1 2 3 +-------------+-------------+-------------+-------------+ | Length | Class-Num | C-Type | +-------------+-------------+-------------+-------------+ | | // (Object contents) // | | +-------------+-------------+-------------+-------------+ An object header has the following fields: Length: 16 bits Length of the object, measured in bytes, including the object header and object contents. Class-Num: 8 bits Identifies object class. Currently, the only one object class is defined. This is the MPLS Stack Entry Object. C-Type: 8 bits Identifies object sub-type. Currently, only one object sub-type is defined. 7.3 MPLS Stack Entry Object Class An instance of the MPLS Entry Object class represents the entire MPLS label stack, formatted exactly as it was when it arrived at the LSR that sends the ICMP message. ICMP Extensions for MPLS July 1999 In the illustration below, bytes 0-3 depict the first member of the MPLS label stack. Each remaining member of the MPLS label stack is represented by another 4 bytes that share the same format. Syntax follows: MPLS Stack Entry Class = 1, C-Type = 1. 0 1 2 3 +-------------+-------------+-------------+-------------+ | Label |EXP |S| TTL | +-------------+-------------+-------------+-------------+ | | // Remaining MPLS Stack Entries // | | +-------------+-------------+-------------+-------------+ Label: 20 bits Exp: Experimental Use, 3 bits S: Bottom of Stack, 1 bit TTL: Time to Live, 8 bits 8.Security Considerations This memo presents no security considerations beyond those already presented by current ICMP applications (e.g., traceroute). 9. References [ARCH], Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol Label Switching Architecture", Internet Draft , July, 1998 [ENCODE], Rosen, E., Rekhter, Y., Tappan, D, Farinacci, D., Fedorkow, G., Li, T., Conta, A., _MPLS Stack Encoding_, Internet Draft, , September 1998. [FRAME], Callon, R., Doolan, P., Feldman, N., Fredette, A., Swallow, G., and A. Viswanathan, "A Framework for Multiprotocol Label Switching", Internet Draft , November 1997. [MPLSATM], Davie, B., Lawrence, J., McCloghrie, K., Rekhter, Y., Rosen, E., Swallow, G, _MPLS using ATM VC Switching_, , November, 1998. [MPLSFRAME], Conta, A., Doolan, P., Malis, A., _Use of Label Switching on Frame Relay Networks_, , November, 1998. ICMP Extensions for MPLS July 1999 [RFC-792], Postel, J., _Internet Control Message Protocol_, RFC 792, ISI, September 1981. [RFC-1812], Baker, F., _Requirements for IP Version 4 Routers_, RFC 1812, June 1995. [RFC-2026], Bradner, S., _Internet Standards Process _ Revision 3_, RFC 2026, Harvard University, October 1996. [RFC-2119], Bradner, S,, "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, Harvard University, March 1997 10. Author's Addresses Ronald P. Bonica MCI WorldCom 2100 Reston Parkway Reston, Virginia, U.S.A. 20191 Phone: +1 703 715 7176 Email: rbonica@mci.net Daniel C. Tappan Cisco Systems 250 Apollo Drive Chelmsford, Massachusetts, 01824 Email: tappan@cisco.com Der-Hwa Gan Juniper Networks 385 Ravendale Drive Mountain View, California 94043 Email: dhg@juniper.net