MPLS Working Group R. Bonica Internet-Draft D. Gan Expires:
February 3,March 24, 2006 Juniper Networks D. Tappan Cisco Systems, Inc. August 2,September 20, 2005 ICMP Extensions for MultiProtocol Label Switching draft-ietf-mpls-icmp-03draft-ietf-mpls-icmp-04 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. 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. This Internet-Draft will expire on February 3,March 24, 2006. Copyright Notice Copyright (C) The Internet Society (2005). Abstract This memo proposes extensionsdefines an extension to ICMP that permitpermits Label Switching Routers to append MPLS information to ICMP messages. This extension has already been widely deployed and this memo is introduced to describe existing practice. Table of Contents 1. Conventions Used In This Document . . . . . . . . . . . . . . . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 43 3. Application to TRACEROUTE .Architectural Considerations . . . . . . . . . . . . . . . . . 54 4. Disclaimer . . . . . . .Application to TRACEROUTE . . . . . . . . . . . . . . . . . . . 64 5. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 5.1 Common Header . . . . . . . . . . . . . . . . . .Disclaimer . . . . 8 5.2 Object Header. . . . . . . . . . . . . . . . . . . . . . 8 5.34 6. MPLS Stack Entry Object Class . . . . . . . . . . . . . . 9 5.4 Extended Payload Object Class . . . . . . . . . . . . . . 10 6. Backward Compatibility. . . . . . . . . . . . . . . . . . . . 115 7. Security Considerations . . . . . . . . . . . . . . . . . . . 12. 6 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13. 6 9. Normative References . . . . . . . . . . . . . . . . . . . . . 136 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 13. . 7 Intellectual Property and Copyright Statements . . . . . . . . 15. . 8 1. 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 RFC2119 . 2. Introduction IP routers use the Internet Control Message Protocol (ICMP)  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". In this document, the term "originaldatagram" refers to the datagramto 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 RFC 3032  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 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 routed the original datagram based upon information contained by the MPLS label stack. This memo proposes extensionsdefines an extension to ICMP that permitpermits 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. The ICMP extensions defined in this document must be preceded by by an ICMP Extension Structure Header and an ICMP Object Header. Both are defined in . 3. Architectural Considerations Only layer 3 information should be included in ICMP messages. MPLS information can be included only in so much as MPLS participates in layer 3 routing. Layer 2 information (e.g., ethernet, PPP) should not be included in ICMP messages. 4. Application to TRACEROUTE ICMP extensions defined in this memo support enhancements to TRACEROUTE. The enhanced TRACEROUTE,TRACEROUTE application, like older implementations, indicates which nodes the original datagram visited en route to its destination. It differs from older implementations in that it also indicatesreflects the original datagramsdatagram's MPLS encapsulation status as it arrived at each node. Figure 1 contains sample output from an enhanced TRACEROUTE implementation. > traceroute 100.100.6.110.100.6.1 traceroute to 100.100.6.1 (100.100.6.1),10.100.6.1 (10.100.6.1), 30 hops max, 40 byte packets 1 10.1.1.2 (10.1.1.2) 0.661 ms 0.618 ms 0.579 ms 2 10.1.12.2 (10.1.12.2) 0.861 ms 0.718 ms 0.679 ms MPLS Label=100048 Exp=0 TTL=1 S=1 3 10.1.24.2 (10.1.24.2) 0.822 ms 0.731 ms 0.708 ms MPLS Label=100016 Exp=0 TTL=1 S=1 4 10.100.6.1 (10.100.6.1) 0.961 ms 8.676 ms 0.875 ms Figure 1: Enhanced TRACEROUTE Sample Output 4.5. Disclaimer This memo does not define the general relationship between ICMP and MPLS. Sections 2.3 and 2.4 of RFC3032 define this relationship. Specifically, this document defers to RFC3032 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 addressesThe current memo does not define encapsulation specific TTL manipulation procedures. It defers to Section 5.4 of RFC 3034  and Section 10 of RFC 3035  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. 5. 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. In theory, the data structure defined herein can be appended to the following ICMP message types: Destination Unreachable Time Exceeded Parameter Problem Source Quench Redirect However, in practice, it would only be useful when appended to the Destination Unreachable and Time Exceeded messages. 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 adjusted appropriately to include the data structure. 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. 5.1 Common Header 0 1 2 3 +-------------+-------------+-------------+-------------+ | Vers | (Reserved) | Checksum | +-------------+-------------+-------------+-------------+ Figure 2: Common Header 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. 5.2 Object Header Every object consists of one or more 32-bit words with a one-word header. The following is the format of the one-word header: +-------------+-------------+-------------+-------------+ | Length | Class-Num | C-Type | +-------------+-------------+-------------+-------------+ | | | // (Object contents) // | | | +-------------+-------------+-------------+-------------+ Figure 3: Object Header An object header has the following fields: Length: 16 bits Length of the object, measured in octets, including the object header and object contents. Class-Num: 8 bits Identifies object class. C-Type: 8 bits Identifies object sub-type. 5.36. MPLS Stack Entry Object ClassThis section defines an ICMP extention object that can be appended to the ICMP Time Exceeded and Destination Unreachable messages. 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 Figure 2 depicts the MPLS Stack Entry Object. It must be preceded by an ICMP Extension Structure Header and an ICMP Object Header. Both are defined in . In the illustration below,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. Syntax follows:MPLS Stack Entry Class = 1, C-Type = 1. 0 1 2 3 +-------------+-------------+-------------+-------------+ | Label |EXP |S| TTL | +-------------+-------------+-------------+-------------+ | | | // Remaining MPLS Stack Entries // | | | +-------------+-------------+-------------+-------------+ Figure 4:2: MPLS Stack Entry Object ClassLabel: 20 bits Exp: Experimental Use, 3 bits S: Bottom of Stack, 1 bit TTL: Time to Live, 8 bits 5.4 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). Syntax follows: MPLS Stack Entry Class = 2, C-Type = 1. 0 1 2 3 +-------------+-------------+-------------+-------------+ | | | // Additional bytes of original datagram // | | | +-------------+-------------+-------------+-------------+ Figure 5: Extended Payload Object Class 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. 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.7. Security Considerations This memo presents no security considerations beyond those already presented by current ICMP applications (e.g., traceroute). 8. IANA Considerations IANA should establish a registry of ICMP extention classesshould reserve an object class and class- sub-types.object type for the MPLS Stack Entry Object from the ICMP Extension Object registry. 9. Normative References  Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.  Postel, J., "Internet Control Message Protocol", STD 5, RFC 792, September 1981.  Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack Encoding", RFC 3032, January 2001.  Bonica, R., "Extending the Internet Control Message Protocol (ICMP)", draft-bonica-internet-icmp-00 (work in progress), September 2005.  Conta, A., Doolan, P., and A. Malis, "Use of Label Switching on Frame Relay Networks Specification", RFC 3034, January 2001.  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.  Baker, F., "Requirements for IP Version 4 Routers", RFC 1812, June 1995.Authors' Addresses Ronald P. Bonica Juniper Networks 2251 Corporate Park Drive Herndon, VA 20171 US Email: firstname.lastname@example.org Der-Hwa Gan Juniper Networks 1194 N. Mathilda Ave. Sunnyvale, CA 94089 US Email: email@example.com Daniel C. 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