Network Working Group Naiming Shen INTERNET DRAFT Albert Tian Expiration Date: October 2004 Redback Networks Derek Yeung Procket Networks April 2004 Inter-Area IP Route Attribute in IS-IS 1. 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/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. 2. Abstract This document describes an extension to the IS-IS protocol to allow some routing attributes to be associated with advertised inter-area prefixes. The extension allows routers to learn this routing information without the knowledge of the link-state topology in another IS-IS level. The initial applications for this extension are inter-area IP MPLS fast reroute for node protection and inter-area TE LSPs. 3. Introduction An IS-IS [1][2] routing domain can be partitioned into multiple levels with L1/L2 border routers redistributing routes between levels. When routes are leaked into another level most of the routing or topology information is lost. However, certain Shen, Tian, Yeung Expires October 2004 [Page 1] Internet Draft Inter-Area Route Attr April 2004 applications requiring network topology information may not be bounded by the IGP area/level. This document proposes to add additional routing attributes during the inter-area route redistribution in inter-area prefix advertisement. IP fast re-route for node protection [3][4] uses the link-state topology information to compute alternative paths to reach next-nexthop IP nodes. When the nexthop node is a border router and the next-nexthop router resides in another IS-IS level, the PLR node won't have the topology information needed to select an inter-area next-nexthop node for node protection. This IS-IS inter-area route attribute extension provides a mechanism for IS-IS border routers to include the required topology information along with intra-area prefixes. 4. Terminology FRR Fast Reroute. Level IS-IS routing level, it is inter-changeable with "area" in this document. Next-Nexthop Node The router is the Nexthop node of PLR's Nexthop node. PLR Point of Local Repair. This node detects the link or nexthop node failure and performs the fast reroute operation. TE LSP MPLS traffic engineer LSP or label switched path. 5. Inter-Area Route Attribute Sub-TLV This document proposes a new "Inter-Area Route Attribute" sub-TLV to be added to TLVs 135 and 235 [5][6]. This sub-TLV includes a list of "Attribute Flag" and a "Router ID". This sub-TLV is only used for IS-IS L1/L2 border router for advertising leaked IP prefixes. The Inter-Area Route Attribute sub-TLV has the following structure: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Attr Flag 1 | Router-ID 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Router-ID 1 (continued) | Attr Flag 2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Shen, Tian, Yeung Expires October 2004 [Page 2] Internet Draft Inter-Area Route Attr April 2004 | Router-ID 2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // // Attr Flag N | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Router-ID N | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type An 8 bit field. The Sub-TLV code value is 4. Length An 8 bit field and the value is 5 * N. N is the number of route attributes in the list. Each route attribute contains an 8-bit attribute flag and a 32-bit Router-ID. Attribute Flag This is a 8-bit field with three bits currently defined. 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |N|O|B| reserved| +-+-+-+-+-+-+-+-+ Bits Description N Nexthop Bit. If set, the router advertising this IP prefix with this sub-TLV uses router specified in the Router-ID field as the nexthop node. O Origination Bit. If set, the router advertising this IP prefix with this sub-TLV had learnt this prefix from the router specified in the Router-ID field. B Non-Best Path Bit. The N bit and B bit are mutually exclusive. If set, the border router advertising this this sub-TLV does not consider router specified in the Router-ID field to be on the IGP best path to reach the IP prefix. For some applications such as traffic engineering, the LSP path setup may not follow the shortest path. Router-ID This is a 32-bit unsigned number representing the router which can be used to forward traffic towards the destination for the prefixes. The list may contain multiple (Attribute Flag, Router-ID) tuples to handle ECMP or non-ECMP cases. Shen, Tian, Yeung Expires October 2004 [Page 3] Internet Draft Inter-Area Route Attr April 2004 6. Applications Determination of when to advertise route attribute associated with an IP prefix using the proposed sub-TLV is application dependent. This document only describes the mechanism for node protection of IP fast reroute. Other applications, such as inter-area TE LSP setup mechanism, are beyond the scope of this document. 6.1. Inter-Area IP node protection using FRR In the IP fast reroute for node protection case, the IS-IS border router can be configured to advertise Inter-Area Route Attribute sub-TLVs along with inter-area prefixes. This can be used by the adjacent PLR nodes to fast reroute traffic to inter-area next-nexthop nodes when the IS-IS border router fails. The Router-ID is the TE router-id [5] advertised by the nexthop router. The Nexthop bit in the Attribute Flag must be set. Whether an inter-area prefix should include this Inter-Area Route Attribute sub-TLV can be determined based on local policy or on the administrative route tags associated with the prefix. The sub-TLV may contain a list of the route attributes in ECMP case. When the IS-IS node (PLR) adjacent to the area border router has an alternative path to a next-nexthop node (in another area) which does not go through the area border router, it can pre-build an alternative IP path for the prefixes and perform the node protection fast switchover when the area border router fails. 7. Security Considerations This document raises no new security issues. 8. Acknowledgments The authors would like to thank Tony Li and Acee Lindem for their comments to this document. 9. IANA Considerations The authors have chosen "4" as the type code for this sub-TLV. This value must be allocated by IANA. 10. Full Copyright Statement Copyright (C) The Internet Society (2002). 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 Shen, Tian, Yeung Expires October 2004 [Page 4] Internet Draft Inter-Area Route Attr April 2004 or assist in its implementation 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 languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS 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. 11. References [1] "Intermediate System to Intermediate System Intra-Domain Routeing Exchange Protocol for use in Conjunction with the Protocol for Providing the Connectionless-mode Network Service (ISO 8473)", ISO 10589. [2] Callon, R., RFC 1195, "Use of OSI IS-IS for routing in TCP/IP and dual environments", RFC 1195, December 1990. [3] Shen, N., Pan, P., "Nexthop Fast ReRoute for IP and MPLS", Internet draft, draft-shen-nhop-fastreroute-00.txt, work in progress. [4] Smit, H., Shen, N., "Calculating IGP Routes Over Traffic Engineering Tunnels", draft-ietf-rtgwg-igp-shortcut-00.txt, Work In Progress. [5] Li, T., and Smit, H., "IS-IS extensions for Traffic Engineering", draft-ietf-isis-traffic-05.txt, Work in Progress, August 2003. [6] Przygienda, Shen, Sheth, "Multi Topology (MT) Routing in IS-IS", draft-ietf-isis-wg-multi-topology-06.txt, Work in progress. 12. Authors' Addresses Naiming Shen Redback Networks, Inc. Shen, Tian, Yeung Expires October 2004 [Page 5] Internet Draft Inter-Area Route Attr April 2004 300 Holger Way San Jose, CA 95134 Email: naiming@redback.com Albert Tian Redback Networks, Inc. 300 Holger Way San Jose, CA 95134 Email: tian@redback.com Derek M. Yeung Procket Networks, Inc. 1100 Cadillac Court Milpitas, CA 95035 USA Email: myeung@procket.com Shen, Tian, Yeung Expires October 2004 [Page 6]