Network Working Group S. Previdi Internet Draft D. Ward L. Ginsberg Expires: February, 2006 A. Roy Cisco Systems, Inc August, 2005 IS-IS Multi-instance Multi-topology draft-previdi-isis-mi-mt-00.txt 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/1id-abstracts.html The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html Previdi, et al [Page 1] Internet Draft Multi-Instance IS-IS August, 2005 Abstract This draft describes a mechanism that allows a single router to share one or more links among multiple IS-IS routing protocol instances. Multiple instances allow the deployment of multiple address-families as well as multiple instances of the same address-family and it is an alternative to Multi-Topology IS-IS. Routers supporting the same instance will form adjacencies, exchange routing updates and compute paths. Each PDU will contain a new TLV identifying the instance to which the PDU belongs. This allows a network operator to deploy multiple IS-IS topologies in parallel, using the same set of links when required and still have the capability of computing topology specific paths. This draft does not address the forwarding paradigm that needs to be used in order to ensure data PDUs are forwarded according to the topology to which they belong. 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 [KEYWORDS]. 2. Introduction IS-IS has been already extended in order to support multiple topologies [MT-ISIS] through the use of additional TLVs in IIH/LSP PDUs. MT-ISIS specifies that a single adjacency, single flooding scheme, and single LSDB are to be shared across all topologies to which a router belongs. This draft describes an alternative approach where multiple topologies are supported by the use of multiple instances of the IS-IS protocol. Routers which support this extension are referred to as "multi-instance capable routers" (MI-RTR). 3. Proposed Solution The solution is based on a new TLV called the Instance Identifier (IID) that is used to mark each routing PDU originated by the router. Routers form adjacencies and exchange routing updates only if their IIDs correspond. Each topology is therefore processed within a separate instance of the IS-IS protocol. This also implies an instance specific flooding scheme, instance specific LSDBs and Instance specific routing calculations. It MAY also imply instance specific routing and forwarding tables. However, Previdi, et al [Page 2] Internet Draft Multi-Instance IS-IS August, 2005 this aspect is outside the scope of this specification. When multiple instances share the same link each instance will have a separate set of adjacencies. Each IS-IS PDU is associated with only one IS-IS instance. How multiple instances are implemented is outside the scope of this specification. 3.1. Instance Identifier (IID) A new TLV is defined in order to convey an instance identifier (IID). The scope of the IID is to mark each IS-IS instance running on a router with a unique 16-bit number. The IID TLV is carried in all IS-IS PDUs (IIH, SNP, LSP) originated by the router. Routers have to exchange and agree on instance numbers so that IIDs can be understood consistently across adjacencies and flooding domain. The following format is used for the IID: TLV: Type: TBD Length: 2 Value: <16-bit number IID> 3.2 Instance Membership Each router can be configured as part of one or more instances of IS-IS. Each instance the router belongs to will correspond to the value advertised in the IID TLV of IS-IS PDUs originated by that instance. Only one IID can be advertised in an IIH, LSP, or SNP PDU. PDUs with multiple IID TLVs MUST be ignored. 3.3 Adjacency Establishment In order to establish adjacencies, IS-IS routers exchange IIH PDUs. Two types of adjacencies exist in IS-IS: point-to-point and broadcast. The following sub-sections describe the additional rules an MI-RTR MUST follow in order to establish adjacencies. 3.3.1 Point-to-Point Adjacencies A new IID TLV is inserted into the p2p hello PDUs originated by an MI-RTR. Upon reception of an IIH, an MI-RTR inspects the received IID TLV and if it matches any of the IIDs configured on that link, normal adjacency establishment procedures are used to establish an instance specific adjacency. Previdi, et al [Page 3] Internet Draft Multi-Instance IS-IS August, 2005 This extension allows an MI-RTR to establish multiple adjacencies to the same neighbor over a p2p link. This differs from the generic behavior of p2p links where only one adjacency is formed. However, in this case IS-IS instances are "ships-in-the-night" and from a logical perspective only one adjacency per instance is formed on p2p links. 3.3.2 Multi-Access Adjacencies Multi-Access (broadcast) networks behave differently than p2p in the sense that a DIS is elected. MI-RTRs will establish adjacencies and elect a DIS per IS-IS instance. Upon reception of an IIH each MI-RTR will form adjacencies only with routers advertising the same IID in their IIH PDUs. Since an MI-RTR is not required to participate in all IIDs on a LAN, it's possible to elect a different DIS for different instances. 3.3.3 Interoperability Considerations It is assumed that any TLV that is not understood is silently ignored without compromising the processing of the whole IS-IS PDU (IIH, LSP, SNP). To a router not implementing this extension, all IS-IS PDUs received will appear to be associated with the standard topology regardless of any IID TLVs which may be contained in those PDUs. This can cause interoperability issues, not all of which can be resolved. Therefore deployment/configuration of MI-RTRs must be done prudently. MI-RTRs may be configured to accept or not to form an adjacency with a router not supporting this extension. In any case, only the IID zero instance can seamlessly interoperate with routers not supporting this extension. 3.3.3.1 Interoperability using p2p networks MI-RTRs supporting IID #0 may interoperate over a p2p link with a router which does NOT support this extension. To do so, an MI-RTR must refrain from sending LSPs and SNPs for instances other than IID #0 over the p2p link. It MUST also refrain from sending IIHs for instance IDs other than zero as these IIHs may affect the state of the adjacency for IID #0 in the neighbor. The presence/absence of the IID TLV in an IIH indicates that the neighbor does/does not support this extension. Once it is determined that the neighbor does not support this extension, an MI-RTR MUST NOT send PDUs (including IIHs) for instances other than IID #0. Previdi, et al [Page 4] Internet Draft Multi-Instance IS-IS August, 2005 Until such time as the capability of the neighbor are known, an implementation MAY send IIHs for any IID on a p2p link. 3.3.3.2 Interoperability using Multi-Access networks The presence on a multi-access network of one or more MI-RTRs supporting one or more non-zero IIDs is incompatible with the presence of any routers which do not support this extension. This is because the necessary transmission of IS-IS PDUs associated with non-zero IIDs will be interpreted as being associated with IID #0 by the routers not supporting this extension. Therefore, use of this extension on a multi-access network requires that all routers are upgraded to a software version supporting this extension. This restriction MAY be applied independently for each level of routing supported on the network. 4. IANA considerations IANA will assign a new codepoint for the MI-MT IID defined in this document and carried within the IIH PDU. Suggest value is XX (to be assigned by IANA). 5. Acknowledgments The authors would like to thank Mike Shand for his valuable input. 6. Normative References [RFC] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels," RFC 2119. [IS-IS] "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. [IS-IS-IP] Callon, R., RFC 1195, "Use of OSI IS-IS for routing in TCP/IP and dual environments", RFC 1195, December 1990. [HMAC-MD5] Li, T. and R. Atkinson, "Intermediate System to Intermediate System (IS-IS) Cryptographic Authentication", RFC 3567, July 2003. [MT-IS-IS] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi Topology (MT) Routing in IS-IS", draft-ietf-isis-wg-multi-topology- 10.txt, May 2005. Previdi, et al [Page 5] Internet Draft Multi-Instance IS-IS August, 2005 7. Security Considerations Security concerns for IS-IS are addressed in the IS-IS specification [IS-IS], and accompanying specifications on [HMAC-MD5]. No additional considerations need to be made for the extension. 8. Authors' Addresses Stefano Previdi Cisco Systems Via Del Serafico, 200 00142 Rome, Italy sprevidi@cisco.com Dave Ward Cisco Systems 170 W. Tasman Dr. San Jose, CA 95134 USA dward@cisco.com Les Ginsberg Cisco Systems 170 W. Tasman Dr. San Jose, CA 95134 USA ginsberg@cisco.com Abhay Roy Cisco Systems 170 W. Tasman Dr. San Jose, CA 95134 USA akr@cisco.com 9. IPR Disclaimer 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 Previdi, et al [Page 6] Internet Draft Multi-Instance IS-IS August, 2005 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. 10. Full 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. 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. 11. Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society. This document expires in February, 2006. Previdi, et al [Page 7]