MPLS Working Group Santosh Esale INTERNET-DRAFT Raveendra Torvi Intended Status: Proposed Standard Juniper Networks Expires: September 14, 2017 Luyuan Fang Microsoft Luay Jalil Verizon March 13, 2017 Fast Reroute for Node Protection in LDP-based LSPs draft-esale-mpls-ldp-node-frr-05 Abstract This document describes procedures to support node protection for unicast Label Switched Paths (LSPs) established by Label Distribution Protocol (LDP). In order to protect a node N, the Point of Local Repair (PLR) of N must discover the Merge Points (MPs) of node N such that traffic can be redirected to them in case of node N failure. Redirecting the traffic around the failed node N depends on existing point-to-point LSPs originated from the PLR to the MPs while bypassing the protected node N. The procedures described in this document are topology independent in a sense that they provide node protection in any topology so long as there is a alternate path in the network that avoids the protected node. Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and 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 Esale, et al. Expires September 14, 2017 [Page 1] INTERNET DRAFT March 13, 2017 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 and License Notice Copyright (c) 2017 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1 Abbreviations . . . . . . . . . . . . . . . . . . . . . . . 4 3. Merge Point (MP) Discovery . . . . . . . . . . . . . . . . . . 4 4. Constructing Bypass LSPs . . . . . . . . . . . . . . . . . . . 5 5. Obtaining Label Mapping from MP . . . . . . . . . . . . . . . . 6 6. Forwarding Considerations . . . . . . . . . . . . . . . . . . . 6 7. Synergy with node protection in mLDP . . . . . . . . . . . . . 7 8. Security Considerations . . . . . . . . . . . . . . . . . . . . 7 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7 11. Normative References . . . . . . . . . . . . . . . . . . . . . 7 12. Informative References . . . . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8 1. Introduction This document describes procedures to support node protection for unicast Label Switched Paths (LSPs) established by Label Distribution Protocol (LDP) [RFC5036]. In order to protect a node N, the Point of Local Repair (PLR) of N must discover the Merge Points (MPs) of node N such that traffic can be redirected to them in case of node N Esale, et al. Expires September 14, 2017 [Page 2] INTERNET DRAFT March 13, 2017 failure. Redirecting the traffic around the failed node N depends on existing explicit path Point-to-Point (P2P) LSPs originated from the PLR LSR to the MPs while bypassing node N. The procedures to setup these P2P LSPs are outside the scope of this document, but one option is to use RSVP-TE based techniques [RFC3209] to accomplish it. Finally, sending traffic from the PLR to the MPs requires the PLR to obtain FEC-label bindings from the MPs. The procedures described in this document relies on Targeted LDP (tLDP) session [RFC5036] for the PLR to obtain such FEC-Label bindings. The procedure described in this document assumes the use of platform- wide label space. The procedures for node protection described in this document fall into the category of local protection. The procedures described in this document apply to LDP LSPs bound to either an IPv4 or IPv6 Prefix FEC element. The procedures described in this document are topology independent in a sense that they provide node protection in any topology so long as there is a alternate path in the network that avoids the protected node. Thus these procedures provide topology independent fast reroute. Esale, et al. Expires September 14, 2017 [Page 3] INTERNET DRAFT March 13, 2017 1.1 Abbreviations PLR: Point of Local Repair - the LSR that redirects the traffic to one or more Merge Point LSRs. MP: Merge Point. Any LSR on the LDP-signaled (multi-point to point) LSP, provided that the path from that LSR to the egress of that LSP is not affected by the failure of the protected node. tLDP: A targeted LDP session is an LDP session between non-directly connected LSRs, established using the LDP extended discovery mechanism. FEC: Forwarding equivalence class. IGP: Interior Gateway Protocol. BR: Border Router. 3. Merge Point (MP) Discovery For a given LSP that traverses the PLR, the protected node N, and a particular neighbor of the protected node, we'll refer to this neighbor as the "next next-hop". Note that from the PLR's perspective the protected node N is the next hop for the FEC associated with that LSP. Likewise, from the protected node's perspective the next next- hop is the next hop for that FEC. If for a given triplet the next next-hop is in the same routing subdomain (area) as the PLR, then that next next-hop acts as the MP for that triplet. For a given LSP traversing a PLR and the node protected by the PLR, the PLR discovers its next next-hops (MPs) that are in the same routing subdomain (IGP area) as the PLR from IGP shortest path first (SPF) calculations. The discovery of next next-hop, depending on an implementation, may not involve any additional SPF, above and beyond what will be needed by either ISIS or OSPF anyway, as the next next- hop, just like the next-hop, is a by-product of SPF computation. Also, the PLR may discover all possible MPs from either its traffic engineering database or link state database. Some implementations MAY need appropriate configuration to populate the traffic engineering database. The traffic engineering database is populated by routing protocols such as ISIS and OSPF or configured statically. If for a given triplet the node protected by the PLR is an Border Router (BR), then the PLR and the next next-hop may end up in different routing subdomain. This could happen when an LSP Esale, et al. Expires September 14, 2017 [Page 4] INTERNET DRAFT March 13, 2017 traversing the PLR and the protected node does not terminate in the same routing subdomain as the PLR. In this situation the PLR may not be able to determine the next next-hop from shortest path first (SPF) calculations, and thus may not be able to use the next next-hop as the MP. In this scenario the PLR uses an "alternative" BR as the MP, where an alternative BR is defined as follows. For a given LSP that traverses the PLR and the (protected) BR, an alternative BR is defined as any BR that advertises into PLR's own routing subdomain reachability to the FEC associated with the LSP. Note that even if a PLR protects an BR, for some of the LSPs traversing the PLR and the BR, the next next-hops may be in the same routing subdomain as the PLR, in which case these next next-hops act as MPs for these LSPs. Note that even if the protected node is not an BR, if an LSP traversing the PLR and the protected node does not terminate in the same routing subdomain as the PLR, then for this LSP the PLR MAY use an alternative BR (as defined earlier), rather than the next next-hop as the MP. When there are several candidate BRs for alternative BR, the LSR MUST select one BR. The algorithm used for the alternative BR selection is a local matter but one option is to select the BR per FEC based on shortest path from PLR to the BR. 4. Constructing Bypass LSPs As mentioned before, redirecting traffic around the failed node N depends on existing explicit path Point-to-Point (P2P) LSPs originated from the PLR to the MPs while bypassing node N. Let's refer to these LSPs as "bypass LSPs". While the procedures to signal these bypass LSPs are outside the scope of this document, this document assumes use of RSVP-TE LSPs [RFC3209] to accomplish it. Once a PLR that protects a given node N discovers the set of MPs associated with itself and the protected node, at the minimum the PLR MUST (automatically) establish bypass LSPs to all these MPs. The bypass LSPs MUST be established prior to the failure of the protected node. One could observe that if the protected node is not an BR and the PLR does not use alternative BR(s) as MP(s), then the set of all the IGP neighbors of the protected node forms a superset of the MPs. Thus it would be sufficient for the PLR to establish bypass LSPs with all the IGP neighbors of the protected node, even though some of these neighbors may not be MPs for any of the LSPs traversing the PLR and the protected node. The bypass LSPs MUST avoid traversing the protected node, which means that the bypass LSPs are explicitly routed LSPs. Of course, using Esale, et al. Expires September 14, 2017 [Page 5] INTERNET DRAFT March 13, 2017 RSVP-TE to establish bypass LSPs allows these LSPs to be explicitly routed. As a given router may act as an MP for more than one LSP traversing the PLR, the protected node, and the MP, the same bypass LSP will be used to protect all those LSPs. 5. Obtaining Label Mapping from MP As mentioned before, sending traffic from the PLR to the MPs requires the PLR to obtain FEC-label bindings from the MPs. The solution described in this document relies on Targeted LDP (tLDP) session [RFC5036] for the PLR to obtain such mappings. Specifically, for a given PLR and the node protected by this PLR, at the minimum the PLR MUST (automatically) establish tLDP with all the MPs associated with this PLR and the protected node. These tLDP sessions MUST be established prior to the failure of the protected node. One could observe that if the protected node is not an BR and the PLR does not use alternative BR(s) as MP(s), then the set of all the IGP neighbors of the protected node forms a superset of the MPs. Thus it will be sufficient for the PLR to (automatically) establish tLDP session with all the IGP neighbors of the protected node - except the PLR - that are in the same area as the PLR, even though some of these neighbors may not be MPs for any of the LSPs traversing the PLR and the protected node. At the minimum for a given tLDP peer the PLR MUST obtain FEC-label mapping for the FEC(s) for which the peer acts as an MP. The PLR MUST obtain this mapping before the failure of the protected node. To obtain this mapping for only these FECs and no other FECs that the peer may maintain, the PLR SHOULD rely on the LDP Downstream on Demand (DoD) procedures [RFC5036]. Otherwise, without relying on the DoD procedures, the PLR may end up receiving from a given tLDP peer FEC-label mappings for all the FECs maintained by the peer, even if the peer does not act as an MP for some of these FECs. If the LDP DoD procedures are not used, then for the purpose of the procedures specified in this draft the only label mappings that SHOULD be exchanged are for the Prefix FEC elements whose PreLen value is either 32 (IPv4), or 128 (IPv6); label mappings for the Prefix FEC elements with any other PreLen value SHOULD NOT be exchanged. When a PLR has one or more BRs acting as MPs, the PLR MAY use the procedures specified in [draft-ietf-mpls-app-aware-tldp] to limit the set of FEC-label mappings received from non-BR MPs to only the mappings for the FECs associated with the LSPs that terminate in the PLR's own routing subdomain (area). 6. Forwarding Considerations When a PLR detects failure of the protected node then rather than Esale, et al. Expires September 14, 2017 [Page 6] INTERNET DRAFT March 13, 2017 swapping an incoming label with a label that the PLR received from the protected node, the PLR swaps the incoming label with the label that the PLR receives from the MP, and then pushes the label associated with the bypass LSP to that MP. To minimize micro-loop during the IGP global convergence PLR may continue to use the bypass LSP during network convergence by adding small delay before switching to a new path. 7. Synergy with node protection in mLDP Both the bypass LSPs and tLDP sessions described in this document could also be used for the purpose of mLDP node protection, as described in [draft-ietf-mpls-mldp-node-protection]. 8. Security Considerations The same security considerations apply as those for the base LDP specification, as described in [RFC5036]. 9. IANA Considerations This document introduces no new IANA Considerations. 10. Acknowledgements We are indebted to Yakov Rekhter for many discussions on this topic. We like to thank Hannes Gredler, Aman Kapoor, Minto Jeyananth, Eric Rosen, Vladimir Blazhkun and Loa Andersson for through review of this document. 11. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3209] D. Awduche, et al., "RSVP-TE: Extensions to RSVP for LSP Tunnels", RFC3209, Decembet 2001. [RFC5036] Andersson, L., Minei, I., and B. Thomas, "LDP Specification", RFC 5036, October 2007. [draft-ietf-mpls-app-aware-tldp] Esale, S., et al.,"Application- aware Targeted LDP", draft-esale-mpls-app-aware-tldp, work in progress. 12. Informative References Esale, et al. Expires September 14, 2017 [Page 7] INTERNET DRAFT March 13, 2017 [RFC7715], IJ. Wijnands, et al., "Multipoint LDP (mLDP) Node Protection", RFC7715, January 2016. Authors' Addresses Santosh Esale Juniper Networks EMail: sesale@juniper.net Raveendra Torvi Juniper Networks EMail: rtorvi@juniper.net Luyuan Fang Microsoft Email: lufang@microsoft.com Luay Jalil Verizon Email: luay.jalil@verizon.com Esale, et al. Expires September 14, 2017 [Page 8]