Network Working Group George Swallow Internet Draft Cisco Systems, Inc. Expiration Date: December 2003 Dan Tappan Cisco Systems, Inc. June 2003 LSR Self-Test draft-swallow-mpls-lsr-self-test-00.txt Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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/1id-abstracts.html The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html Copyright (C) The Internet Society (2003). All Rights Reserved. Abstract Abstract This document defines a means of self test for a Label-Switched Router (LSR) to verify that its dataplane is functioning for certain key Multi-Protocol Label Switching (MPLS) applications including unicast forwarding based on LDP [LDP] and traffic engineering tunnels based on [RSVP-TE]. A new Loopback FEC type is defined to allow an upstream neighbor to assist in the testing at very low cost. MPLS Echo Request and MPLS Echo Reply messages [LSP-Ping] messages are extended to do the actually probing. Swallow & Tappan [Page 1] Internet Draft draft-swallow-mpls-lsr-self-test-01.txt June 2003 Contents 1 Introduction ........................................... 4 1.1 Conventions ............................................ 4 2 Loopback FEC ........................................... 5 2.1 Loopback FEC Element ................................... 5 2.2 LDP Procedures ......................................... 6 3 Data Plane Self Test ................................... 6 3.1 Next Hop Verification Object ........................... 7 3.2 Additional Error Codes ................................. 9 3.3 Sending procedures ..................................... 9 3.4 Receiving procedures ................................... 10 3.5 Upstream Neighbor Verification ......................... 11 4 Security Considerations ................................ 11 5 IANA Considerations .................................... 12 6 Acknowledgments ........................................ 12 7 References ............................................. 12 7.1 Normative References ................................... 12 7.2 Informative References ................................. 12 8 Authors' Addresses ..................................... 13 0. Sub-IP ID Summary (This section to be removed before publication.) (See Abstract above.) RELATED DOCUMENTS May be found in the "references" section. WHERE DOES IT FIT IN THE PICTURE OF THE SUB-IP WORK Fits in the MPLS box. WHY IS IT TARGETED AT THIS WG MPLS WG is currently looking at MPLS-specific error detection and recovery mechanisms. The mechanisms proposed here are for packet- based MPLS LSPs, which is why the MPLS WG is targeted. JUSTIFICATION The WG should consider this document, as it allows network Swallow & Tappan [Page 2] Internet Draft draft-swallow-mpls-lsr-self-test-01.txt June 2003 operators to detect MPLS LSP data plane failures in the network. This type of failures have occurred, and are a source of concern to operators implementing MPLS networks. Swallow & Tappan [Page 3] Internet Draft draft-swallow-mpls-lsr-self-test-01.txt June 2003 1. Introduction This document defines a means of self test for a Label-Switched Router (LSR) to verify that its dataplane is functioning for certain key Multi-Protocol Label Switching (MPLS) applications including unicast forwarding based on LDP [LDP] and traffic engineering tunnels based on [RSVP-TE]. MPLS Echo Request and MPLS Echo Reply messages [LSP-Ping] messages are extended to do the actually probing. The pings are sent to an upstream neighbor, looped back through the LSR under test and intercepted, by means of TTL expiration by a downstream neighbor. Extensions to LSP-Ping are defined to allow the down stream neighbor to verify the test results. In order to minimize the load on upstream LSRs a new loopback FEC is defined. Receipt of a packet labeled with a loopback label will cause the advertising LSR to pop the label off the label stack and send the packet out the advertised interface. Note that use of a loopback allows an LSR to label entries for which the LSR is not currently its potential upstream neighbor's next hop. In this way label entries can be verified prior to the occurrence of a routing change. Some routing protocls, most notably OSPF have no means of exchanging "Link Local Identifiers" used to identify unnumbered links and components of bundled links. These same test procedures can be used to associate the neighbor's interfaces with the probing LSRs interfaces. This is achieved by simply having the TTL of the MPLS Ping expire one hop sooner, i.e. at the testing LSR itself. 1.1. Conventions 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 [KEYWORDS]. Swallow & Tappan [Page 4] Internet Draft draft-swallow-mpls-lsr-self-test-01.txt June 2003 2. Loopback FEC The Loopback FEC type is defined to enable an upstream neighbor to assist in the LSR self-testing at very low cost. This FEC allows the loopback to occur in the dataplane without control plane involvement beyond the initial LDP exchange and dataplane setup. An LSR uses the Loopback FEC to selectively advertise loopback labels to its neighbor LSRs. Each loopback label is bound to a particular interface. For multiaccess links, one label per neighbor is required since the link-level address is derived from the label lookup. When an MPLS packet with its top label set to a loopback label is received from an interface over which that label was advertised, the loopback label is popped and the packet is sent on the interface to which the loopback label was bound. TTL treatment for loopback labels follows the Uniform model. I.e. the TTL carried in the loopback label is decremented and copied to the exposed label or IP header as the case may be. 2.1. Loopback FEC Element FEC element type 130 is used. The FEC element is encoded as follows: (note: 130 is provisionally assigned, the actual value will be assigned by IANA.) 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 130 | Res | Interface Type| Id Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Interface Identifier | | " | | " | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Reserved Must be set to zero on transmission and ignored on receipt. Swallow & Tappan [Page 5] Internet Draft draft-swallow-mpls-lsr-self-test-01.txt June 2003 Interface Type # Type Interface Identifier --- ---- -------------------- 0 Unnumbered A 32 bit Link Identifier as defined in [RFC3477] 1 IPv4 Numbered IPv4 Address 2 IPv6 Numbered IPv6 Address Identifier Length Length of the interface identifier in octets. Address An identifier encoded according to the Identifier Type field. The length is 4 bytes for Unnumbered and IPv4, 16 bytes for IPv6. 2.2. LDP Procedures It is RECOMMENDED that loopback labels only be distributed in response to a Label Request message, irrespective of the label advertisement mode of the LDP session. However it is recognized that in certain cases such as OSPF with unnumbered links, the upstream LSR may not have sufficiently detailed information of the neighbors link identifier to form the request. In these cases, the downstream LSR will need to be configured to make unsolicited advertisements. 3. Data Plane Self Test A self test operation involves three LSRs, the LSR doing the test, an upstream neighbor and a downstream neighbor. We refer to these as LSRs T, U, and D respectively. The packet flow is shown below. Although the figure shows LSRD adjacent to LSRT it may in some cases be an arbitrary number of hops away. Swallow & Tappan [Page 6] Internet Draft draft-swallow-mpls-lsr-self-test-01.txt June 2003 +------+ +------+ +------+ | ,-|-------|- | | | | <-|-------|- | | | | | | | | | +------+ +------+ +------+ LSRU LSRT LSRD Figure 2: Upstream Neighbor Verification No TLVs need to be included in the MPLS Echo Request. By noting the Sender's Handle and Sequence Number, as well as the loopback label, LSRT is able to detect that a) the packet was looped, and b) determine (or verify) the interface on which the packet was received. A Next Hop Verification TLV may be included to assist in verification. This may be particularly useful in a system where control is distributed over multiple processor. 4. Security Considerations Were loopback labels widely known, they might be subject to abuse. It is therefore RECOMMENDED that loopback labels only be shared between trusted neighbors. Further, if the loopback labels are drawn from the Global Label Space, or any other label space shared across multiple LDP sessions, it is RECOMMENDED that all loopback label be filtered from a session except those labels pertaining to interfaces directly connected to the neighbor participating in that session. Swallow & Tappan [Page 11] Internet Draft draft-swallow-mpls-lsr-self-test-01.txt June 2003 5. IANA Considerations TBD 6. Acknowledgments The authors would like to thank Kireeti Kompella, Vanson Lim, Tom Nadeau, and Bob Thomas for their comments and suggestions. 7. References 7.1. Normative References [RFC3036] Andersson, L. et al., "LDP Specification", January 2001. [LSP-Ping] Bonica, R. et al., "Detecting MPLS Data Plane Liveness", work-in-progress. [RFC3477] Kompella, K. & Y. Rekhter, "Signalling Unnumbered Links in Resource ReSerVation Protocol - Traffic Engineering (RSVP-TE)", January 2003. [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 7.2. Informative References [RSVP-TE] Awduche, D., et al, "RSVP-TE: Extensions to RSVP for LSP tunnels", RFC 3209, December 2001. Swallow & Tappan [Page 12] Internet Draft draft-swallow-mpls-lsr-self-test-01.txt June 2003 8. Authors' Addresses George Swallow Cisco Systems, Inc. 1414 Massachusetts Ave Boxborough, MA 01719 Email: swallow@cisco.com Dan Tappan Cisco Systems, Inc. 1414 Massachusetts Ave Boxborough, MA 01719 Email: tappan@cisco.com Swallow & Tappan [Page 13]