Internet Draft MPLS Working Group R.Bonica Internet Draft MCIWorldCom Document: draft-ietf-mpls-icmp-02.txt D.Tappan Cisco Systems D.Gan Juniper Networks August 2000 ICMP Extensions for MultiProtocol Label Switching 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 Label Switching Routers 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" in this document 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 diagnose routing problems. Bonica, Tappan, Hwa Draft-Expires February 2001 1 ICMP Extensions for MPLS August 2000 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". In this document, the term "original datagram" refers to the datagram to which the ICMP message is a response. MPLS Label Switching Routers (LSR) 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 encapsulated datagram, it removes the entire MPLS label stack, exposing the previously encapsulated IP datagram. The LSR then submits the IP datagram to a network-forwarding module for error processing. 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, includes 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 routed the original datagram based upon information contained by the MPLS label stack. The current memo proposes extensions to ICMP that permit an LSR to append MPLS label stack information to ICMP messages. ICMP messages regarding 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 octets of the original datagram. Network operators will use this information to diagnose routing problems. 4. Motivation ICMP extensions defined in the current memo support enhancements to TRACEROUTE. The enhanced TRACEROUTE, like older implementations, indicates which nodes the original datagram visited en route to its ultimate destination. It differs from older implementations in that it also indicates the original datagrams MPLS encapsulation status as it arrived at each node. Figure 1 contains sample output from an enhanced TRACEROUTE implementation. Bonica,Tappan,Gan Draft-Expires February 2001 2 ICMP Extensions for MPLS August 2000 >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 an LSR emits 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. The current memo does not address extensions to ICMPv6. These should be addressed in a separate draft. 6. Formal Syntax This section defines a data structure that an LSR can append to selected ICMP messages. The data structure contains the MPLS label stack that encapsulated the original datagram when it arrived at the LSR. The data structure defined herein can be appended to the following ICMP message types: Bonica,Tappan,Gan Draft-Expires February 2001 3 ICMP Extensions for MPLS August 2000 1) Destination Unreachable 2) Time Exceeded 3) Parameter Problem 4) Source Quench 5) Redirect According to RFC-792, bytes 0 through 19 of any ICMP message contain a header whose format is analogous to that of the IP datagram. Bytes 20 through 23 contain an ICMP message type, code and checksum. Bytes 24 through 27 contain message specific data. Also according to RFC-792, the final field contained by each of the ICMP message types listed above begins at byte 28. It reflects the IP header and leading 64 bits of the original datagram. [RFC-1812] recommends that this final field be extended to include as much of the original datagram as possible. When an LSR appends the data structure defined herein to an ICMP message, the final field of the ICMP message body MUST contain the first 128 octets of the original datagram. At least 20 of these 128 octets represent the IP header of the original datagram. If the original datagram was shorter than 128 octets, the final field MUST be padded with 0's. When an LSR appends the data structure defined herein to an ICMP message, the ICMP "total length" MUST be equal to the data structure length plus 156. The first octet of the data structure must be displaced 156 octets from the beginning of the ICMP message. 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, two object classes are defined. One object class contains an entire MPLS label stack, formatted exactly as it was when it arrived at the LSR that sends the ICMP message. The other contains some portion of the original datagram that could not be included in the final field of the ICMP message body (i.e., the octet 129 and beyond). Both object classes are optional. In the future, additional object classes may be defined. Bonica,Tappan,Gan Draft-Expires February 2001 4 ICMP Extensions for MPLS August 2000 6.1 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 2. 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, the ICMP message does not include the extensions described in this memo. This, however, does not imply that the ICMP message is malformed. It may be in strict compliance with RFC-1812. Reserved: Must be set to 0. 6.2 Object Header Every object consists of one or more 32-bit words with a one-word header, with the following format: +-------------+-------------+-------------+-------------+ | Length | Class-Num | C-Type | +-------------+-------------+-------------+-------------+ | | | // (Object contents) // | | | +-------------+-------------+-------------+-------------+ An object header has the following fields: Length: 16 bits Length of the object, measured in octets, including the object header and object contents. Bonica,Tappan,Gan Draft-Expires February 2001 5 ICMP Extensions for MPLS August 2000 Class-Num: 8 bits Identifies object class. C-Type: 8 bits Identifies object sub-type. 6.3 MPLS Stack Entry Object Class A single 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 In the illustration below, 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. 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 6.4 Extended Payload Object Class An instance of the Extended Payload Object class represents some portion of the original datagram that could not be fit in the final field of the ICMP message body (i.e., octets beyond 128). Bonica,Tappan,Gan Draft-Expires February 2001 6 ICMP Extensions for MPLS August 2000 Syntax follows: MPLS Stack Entry Class = 2, C-Type = 1. 0 1 2 3 +-------------+-------------+-------------+-------------+ | | | // Additional bytes of original datagram // | | | +-------------+-------------+-------------+-------------+ 7. 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. The extensions defined herein are in keeping with the spirit, if not the letter of RFC-1812. In order to support IP-in-IP tunneling, RFC- 1812 extends the final field of selected ICMP messages to include a greater portion of the original datagram. Unfortunately, it extends this field to a variable length without adding a length attribute. This memo binds the length of that final field to an arbitrarily large value (128 octets). Fixing the length of that field facilitates extension of the ICMP message. An additional object is provided through which octets 129 and beyond can be appended to the ICMP message. As few datagrams contain L3 or L4 header information beyond octet 128, it is unlikely that the extensions described herein will disable any applications that rely upon RFC-1812 style ICMP messages. 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, August, 1999 Bonica,Tappan,Gan Draft-Expires February 2001 7 ICMP Extensions for MPLS August 2000 [ENCODE], Rosen, E., Rekhter, Y., Tappan, D, Farinacci, D., Fedorkow, G., Li, T., Conta, A., "MPLS Stack Encoding", Internet Draft, , September 1999. [MPLSATM], Davie, B., Lawrence, J., McCloghrie, K., Rekhter, Y., Rosen, E., Swallow, G, "MPLS using LDP and ATM VC Switching", , June 2000. [MPLSFRAME], Conta, A., Doolan, P., Malis, A., "Use of Label Switching on Frame Relay Networks", <draft-ietf-mpls-fr-06.txt>, June, 2000. [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. Acknowledgments Thanks to Yakov Rekhter and Mike Heard for their contributions to this memo. 11. Author's Addresses Ronald P. Bonica MCI WorldCom 22001 Loudoun County Pkwy Ashburn, Virginia, 20147 Phone: 703 886 1681 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 Bonica,Tappan,Gan Draft-Expires February 2001 8 ICMP Extensions for MPLS August 2000 Email: dhg@juniper.net Bonica,Tappan,Gan Draft-Expires February 2001 9 ICMP Extensions for MPLS August 2000 Full Copyright Statement "Copyright (C) The Internet Society (date). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implmentation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into Bonica,Tappan,Gan Draft-Expires February 2001 10