INTERNET DRAFT IS-IS Multi-instance Multi-topology Jun 2006 Network Working Group S. Previdi Internet Draft L. Ginsberg Expiration Date: Dec 2006 M. Shand A. Roy D. Ward Cisco Systems June 2006 IS-IS Multi-instance Multi-topology draft-previdi-isis-mi-mt-01.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 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 Previdi Expires Dec 2006 [Page 1] INTERNET DRAFT IS-IS Multi-instance Multi-topology Jun 2006 an alternative to Multi-Topology IS-IS. Routers will form instance specific adjacencies, exchange instance specific routing updates and compute paths utilizing instance specific LSDB information. 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. Table of Contents 1. Conventions used in this document..............................2 2. Introduction...................................................2 3. Proposed Solution..............................................3 3.1 Instance Identifier..........................................3 3.2 Instance Membership..........................................3 3.3 Adjacency Establishment......................................4 3.3.1 Point-to-Point Adjacencies................................4 3.3.2 Multi-Access Adjacencies..................................4 3.4 Interoperability Considerations..............................4 3.4.1 MI-ISIS Layer 2 multicast address.........................5 3.4.2 Interoperability using p2p networks.......................5 3.4.3 Interoperability using Broadcast networks.................5 4. Security Considerations........................................6 5. IANA Considerations............................................6 6. Normative References...........................................6 7. Acknowledgments................................................6 8. Authors' Addresses.............................................7 9. Full Copyright Statement.......................................7 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 [BCP14]. 2. Introduction "[MT-IS-IS] defines extensions to IS-IS which support multiple topologies through the use of additional TLVs in IIH/LSP PDUs. [MT- IS-IS] specifies that a single adjacency, single flooding scheme, and single LSDB are to be shared across all topologies to which a Previdi Expires Dec 2006 [Page 2] INTERNET DRAFT IS-IS Multi-instance Multi-topology Jun 2006 router belongs. This draft describes an alternative approach where multiple topologies are supported by the use of multiple independent 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 IS-IS 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, 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 A new TLV is defined in order to convey an instance identifier (IID). The purpose 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. Multiple instances of IS-IS may co-exist on the same network and on the same physical router. IIDs MUST be unique within the same routing domain. Instance identifier #0 is reserved for the standard topology supported by legacy systems. The following format is used for the IID: Type TBA by IANA Length 2 Value <16-bit number IID> 3.2 Instance Membership Each router is configured to be participating in one or more instances of IS-IS. For each instance in which it participates, a router labels all IS-IS PDUs (IIH, LSP or SNP) generated pertaining to that instance by including the appropriate IID TLV. Note that this applies for the standard topology (instance identifier #0). A Previdi Expires Dec 2006 [Page 3] INTERNET DRAFT IS-IS Multi-instance Multi-topology Jun 2006 PDU can only be labeled with a single instance identifier. 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 when establishing 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. This extension allows an MI-RTR to establish multiple adjacencies to the same physical neighbor over a p2p link. This differs from the normal behavior on 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 that PDUs sent by one router are visible to all routers and all routers must agree on the election of a DIS. 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. 3.4 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 unless the mechanisms and procedures discussed below are followed. Previdi Expires Dec 2006 [Page 4] INTERNET DRAFT IS-IS Multi-instance Multi-topology Jun 2006 3.4.1 MI-ISIS Layer 2 multicast address In order for routers to correctly interoperate with routers not implementing this extension and in order not to cause disruption, a specific and dedicated MAC address is used for multicasting IS-IS PDUs labeled with any non-zero IID among MI-RTRs. Each level will use a specific layer 2 multicast address. Such an address allows MI- RTRs to exchange IS-IS PDUs with non-zero IIDs without these PDUs being processed by legacy routers and therefore no disruption is caused. An MI-RTR will exchange ISIS PDUs intended for IID #0 using AllL1IS and AllL2IS ISIS mac layer addresses (as defined in [IS-IS]) and will use two new (TBD) dedicated layer 2 multicast addresses (one for each level) when sending IS-IS PDUs for any non-zero IID. MI-RTRs MUST discard IS-IS PDUs received if either of the following is true: . The destination multicast address is AllL1IS or AllL2IS and the PDU contains an IID TLV with non-zero value. . The destination multicast address is one of the two new addresses and the PDU contains an IID TLV with a zero value or has no IID TLV. 3.4.2 Interoperability using p2p networks In order for an instance on an MI-RTR which participates in the standard topology (IID #0) to interoperate over a p2p link with a router which does NOT support this extension, the MI-RTR MUST NOT send IS-IS PDUs for instances other than IID #0 over the p2p link as these PDUs may affect the state of 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. 3.4.3 Interoperability using Broadcast networks If the multicast addresses AllL1IS and/or AllL2IS are improperly used to send IS-IS PDUs for non-zero IIDs, legacy systems will interpret these PDUs as being associated with IID #0. This will cause inconsistencies in the LSDB in those routers, may incorrectly maintain adjacencies, and may lead to inconsistent DIS election. Previdi Expires Dec 2006 [Page 5] INTERNET DRAFT IS-IS Multi-instance Multi-topology Jun 2006 4. 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. 5. IANA Considerations This document requires the definition a new ISIS TLV that needs to be reflected in the ISIS TLV code-point registry: Type Description IIH LSP SNP ---- ----------------------------------- --- --- --- TBA MI-MT IID y y y 6. Normative References [IS-IS] ISO, "Intermediate system to Intermediate system routeing information exchange protocol for use in conjunction with the Protocol for providing the Connectionless-mode Network Service (ISO 8473)," ISO/IEC 10589:2002, Second Edition. [MT-IS-IS] Pryzgienda, T., Shen, N., and Sheth, N., "Multi Topology (MT) Routing in IS-IS", draft-ietf-isis-wg-multi- topology-11.txt (work in progress), October 2005. [HMAC-MD5] Li, T. and R. Atkinson, "Intermediate System to Intermediate System (IS-IS) Cryptographic Authentication", RFC 3567, July 2003. [BCP9] Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9, RFC 2026, October 1996. [BCP14] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997 [BCP26] Narten, T. and Alvestrand, H., "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26 , RFC 2434, October 1998 [BCP79] Bradner, S. Ed., "Intellectual Property Rights in IETF Technology ", BCP 79 , RFC 3979, March 2005 7. Acknowledgments The authors would like to acknowledge contributions made by Dino Farinacci. Previdi Expires Dec 2006 [Page 6] INTERNET DRAFT IS-IS Multi-instance Multi-topology Jun 2006 8. Authors' Addresses Stefano Previdi CISCO Systems, Inc. Via Del Serafico 200 00142 - Roma ITALY Email: sprevidi@cisco.com Les Ginsberg Cisco Systems 510 McCarthy Blvd. Milpitas, Ca. 95035 USA Email: ginsberg@cisco.com Abhay Roy Cisco Systems 170 W. Tasman Dr. San Jose, CA 95134 USA akr@cisco.com Mike Shand Cisco Systems 250 Longwater Avenue, Reading, Berkshire, RG2 6GB UK Email: mshand@cisco.com Dave Ward Cisco Systems 170 W. Tasman Dr. San Jose, CA 95134 USA dward@cisco.com 9. Full Copyright Statement Copyright (C) The Internet Society (2006). 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 Previdi Expires Dec 2006 [Page 7] INTERNET DRAFT IS-IS Multi-instance Multi-topology Jun 2006 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it 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. 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. Previdi Expires Dec 2006 [Page 8]