Network Working Group B Decraene Internet Draft JL Le Roux Document: draft-decraene-mpls-ldp-interarea-01.txt France Telecom Expiration Date: April 2006 I Minei Juniper Networks, Inc. Proposed Status: Informational October 2005 LDP extensions for Inter-Area LSP 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. Abstract To facilitate the establishment of Label Switched Paths (LSP) that would span multiple IGP areas in a given Autonomous System (AS), this document proposes a new optional label mapping procedure for the Label Distribution Protocol (LDP). This procedure allows the use of a label if the Forwarding Equivalence Class (FEC) Element matches an entry in the routing table (RIB). Matching is defined by an IP longest match search and does not mandate an exact match. Decraene Expires April 2005 [Page 1]
Internet Draft LDP extensions for Inter Area LSP October 2005 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 RFC-2119 [1]. IGP Area: OSPF Area or IS-IS level ABR: OSPF Area Border Router or ISIS L1/L2 router 2. Introduction Link state IGP such as OSPF [RFC 2328] and IS-IS [RFC-1195] allows the partition of an autonomous system into areas or levels so as to increase routing scalability within a routing domain. However, LDP requires that the IP address of the FEC Element should *exactly* match an entry in the IP RIB: according to [LDP] section 3.5.7.1 (Label Mapping Messages Procedures) "An LSR receiving a Label Mapping message from a downstream LSR for a Prefix or Host Address FEC Element should not use the label for forwarding unless its routing table contains an entry that exactly matches the FEC Element. Therefore, the establishment of MPLS LSPs between LERs across areas/levels requires the redistribution of the exact (/32 for IPv4) loopback addresses of all the LERs across all areas. As a consequence, the potential benefits that a multi-area domain may yield are diminished since the number of IP entries in the LSDB, RIB and FIB maintained by every LSR of the domain (whatever the area/level it belongs to) cannot be minimized. Note however that IP prefixes and IGP events may still be reduced since IP addresses of links are usually not redistributed outside of their area. In that context, this document extend the Label Mapping Procedure defined in LDP so as to support the setup of inter-area LSPs while maintaining IP prefixes aggregation on the ABRs. This basically consists of extending the Label Mapping procedure so as to allow for "Longest Match Based" Label Mapping. 3. Label Mapping Procedure This document defines a new label mapping procedure for LDP. It MUST be possible to activate/deactivate this procedure by configuration and it SHOULD be deactivated by default. It MAY be possible to activate it on a per prefix basis. Decraene Expires April 2006 [Page 2]
Internet Draft LDP extensions for Inter Area LSP October 2005 With this new label mapping procedure, a LSR receiving a Label Mapping message from a neighbor LSR for a Prefix Address FEC Element SHOULD use the label for MPLS forwarding if its routing table contains an entry that matches the FEC Element and the advertising LSR is a next hop to reach the FEC. If so, it SHOULD advertise the FEC Element and a label to its LDP peers. By "matching FEC Element", one should understand an IP longest match. Note that with this new Label Mapping Procedure, each LSP established by LDP still strictly follows the shortest path(s) defined by the IGP. FECs selected by this "Longest Match" label mapping procedure will be distributed in an ordered way. However this procedure is applicable to both independent and ordered distribution control mode. 4. Application examples 4.1. Inter-area LSPs Consider the following example of an autonomous system with one backbone area and two edge areas: Area "B" Level 2 / Backbone area +---------------------------+ Area "A" | | Area "C" | | Level 1 | | Level 1 / area | P1 | +----------+ +-------------+ | | P2 | PE1 | 10.0.0.1/32 | | | | |PE4 ABR2 ABR1 PE2 | 10.0.0.2/32 | | P3 | | | | | PE3 | 10.0.0.3/32 +----------+ +-------------+ | | +---------------------------+ Figure 1: An IGP domain with two areas attached to the Backbone Area. Note that this applies equally to IS-IS and OSPF. An ABR refers here either to an OSPF ABR or to an ISIS L1/L2 node. Decraene Expires April 2006 [Page 3]
Internet Draft LDP extensions for Inter Area LSP October 2005 All routers are MPLS enabled and MPLS connectivity (LSP) is required between all PE routers. In the "egress" area "C", the records available are: IGP RIB LDP FEC elements: 10.0.0.1/32 10.0.0.1/32 10.0.0.2/32 10.0.0.2/32 10.0.0.3/32 10.0.0.3/32 The area border router ABR1 advertises in the backbone area: - the aggregated IP prefix 10.0.0/24 in the IGP - all the individual IP FEC elements (/32) in LDP In "backbone" area "B", the records available are: IGP RIB LDP FEC elements: 10.0.0.0/24 10.0.0.1/32 10.0.0.2/32 10.0.0.3/32 The area border router ABR2 advertises in the area "A": - an aggregated IP prefix 10.0/16 in the IGP - all the individual IP FEC elements (/32) in LDP In the "ingress" area "A", the records available are: IGP RIB LDP FEC elements: 10.0/16 10.0.0.1/32 10.0.0.2/32 10.0.0.3/32 In this situation, one LSP is established between ingress PE4 and every egress PE of area C. 4.2. Use of static routes Consider the following example where a LER is dual connected to two LSRs: Decraene Expires April 2006 [Page 4]
Internet Draft LDP extensions for Inter Area LSP October 2005 +--------LSR1---- . | | LER | | | +--------LSR2---- . Figure 2: LER dual connected to two LSRs. In some situations, especially on the edge of the network, it is valid to use static IP routes between the LER and the two LSRs. If necessary, the BFD protocol can be used to quickly detect loss of connectivity. The current [LDP] specification would require on the ingress LER the configuration and the maintenance of one IP route per egress LER and per outgoing interface. The new longest match Label Mapping Procedure described in this document would only require one IP route per outgoing interface. 5. Caveats for deployment 5.1. Deployment consideration LSRs compliant with this document are backward compatible with LSRs that comply with [LDP]. For the successful establishment of end to end MPLS LSPs whose FEC are aggregated in the RIB, this new behavior must be implemented on all LSR in all areas where IP aggregation is used. If all IP prefixes are leaked in the backbone area and only stub areas use IP aggregation, LSRs in the backbone area don't need to be compliant with this document. 5.2. Impact on routing convergence time In case of an egress LER failure in an area, performing IP route aggregation on ABRs will change the routing convergence behavior. The IGP will not propagate the notification of the egress LER failure outside of the egress area and failure notification will rely on LDP signaling through the end to end propagation of the LDP withdraw message. This failure notification may be faster or longer depending on the implementations, the IGP timers used and the network topology (network diameter). For link and P (LSR) node failures, the failure notification is unchanged and the convergence time is expected to be improved because RIB and FIBs have fewer entries to update. Decraene Expires April 2006 [Page 5]
Internet Draft LDP extensions for Inter Area LSP October 2005 6. Security Considerations The "Longest Match" Label Mapping procedure described in this document does not introduce any change as far as the Security Consideration section of [LDP] is concerned. 7. Normative References [LDP] L. Andersson, P. Doolan, N. Feldman, A. Fredette, B. Thomas, "LDP Specification", RFC 3036, January 2001 [MPLS] E. Rosen, A. Viswanathan, R. Callon, " Multiprotocol Label Switching Architecture", RFC 3031, January 2001 [MP-BGP] Bates, T., Rekhter, Y, Chandra, R. and D. Katz, "Multiprotocol Extensions for BGP-4", RFC 2858, June 2000. [BGP L3 VPN] E. Rosen, Y. Rekhter, "BGP/MPLS VPNs", RFC 2547, March 1999 [3107] Y. Rekhter, E. Rosen, "Carrying Label Information in BGP-4", RFC 3107, May 2001 [OSPF] J. Moy, "OSPF Version 2", RFC 1583, March 1994 [IS-IS] R. Callon, "Use of OSI IS-IS for Routing in TCP/IP and Dual Environments", RFC 1195, December 1990 8. Informative Reference [BGP L2 VPN] K. Kompella, Y. Rekhter "Virtual Private LAN Service", draft-ietf-l2vpn-vpls-bgp-05.txt April 8, 2005, work in progress. 9. Acknowledgments Authors would like to thank Yakov Rekhter, Stefano Previdi, Benoit Fondeviole, Gilles Bourdon and Christian Jacquenet for the useful discussions on this subject, their review and comments. 10. Author's Addresses Bruno Decraene France Telecom 38-40 rue du General Leclerc 92794 Issy Moulineaux cedex 9 France bruno.decraene@francetelecom.com Decraene Expires April 2006 [Page 6]
Internet Draft LDP extensions for Inter Area LSP October 2005 Jean-Louis Le Roux France Telecom 2, avenue Pierre-Marzin 22307 Lannion Cedex France jeanlouis.leroux@francetelecom.com Ina Minei Juniper Networks 1194 N. Mathilda Ave. Sunnyvale, CA 94089 ina@juniper.net Intellectual Property Considerations The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf- ipr@ietf.org. Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Decraene Expires April 2006 [Page 7]
Internet Draft LDP extensions for Inter Area LSP October 2005 Copyright Statement Copyright (C) The Internet Society (2005). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Decraene Expires April 2006 [Page 8]