INTERNET-DRAFT Danny McPherson (Ed.) Arbor Networks Les Ginsberg Stefano Previdi Mike Shand Cisco Systems Expires: December 2008 June 25, 2008 Intended Status: Proposed Standard Simplified Extension of LSP Space for IS-IS 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 Copyright Notice Copyright (C) The IETF Trust (2008). McPherson, et al. [Page 1] INTERNET-DRAFT Expires: December 2008 June 2008 Abstract This draft describes a simplified method for extending the LSP space beyond the 256 Link State PDU (LSP) limit defined in [ISO 10589]. This method is intended as a preferred replacement for the method defined in [RFC 3786]. McPherson, et al. [Page 2] INTERNET-DRAFT Expires: December 2008 June 2008 Table of Contents 1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Specification of Requirements. . . . . . . . . . . . . . . . . 4 3. Definition of Commonly Used Terms. . . . . . . . . . . . . . . 4 4. Utilizing Additional System IDs. . . . . . . . . . . . . . . . 5 4.1. Additional Information in Extended LSPs . . . . . . . . . . 5 4.2. Extended LSP Restrictions . . . . . . . . . . . . . . . . . 6 4.2.1. TLVs Which MUST NOT Appear . . . . . . . . . . . . . . . 6 4.2.2. Leaf Advertisements in Extended LSPs . . . . . . . . . . 6 4.2.3. IS Neigbor Advertisement Restrictions. . . . . . . . . . 7 4.2.4. Area Adresses. . . . . . . . . . . . . . . . . . . . . . 8 4.2.5. Overload, Attached, Partition Repair Bits. . . . . . . . 8 4.3. Originating LSP Requirements. . . . . . . . . . . . . . . . 8 4.4. IS Alias ID TLV (IS-Alias). . . . . . . . . . . . . . . . . 8 4.5. New TLVs in Support of IS Neighbor Attributes . . . . . . . 9 5. Comparison with the RFC 3786 Solution. . . . . . . . . . . . . 10 6. Deployment Considerations. . . . . . . . . . . . . . . . . . . 10 6.1. Advertising New TLVs in Extended LSPs . . . . . . . . . . . 11 6.2. Reachability and non-SPF TLV Staleness. . . . . . . . . . . 11 6.3. Normal LSP OL State and Use of Extended LSPs. . . . . . . . 11 6.4. Moving Neighbor Attribute INFO LSPs . . . . . . . . . . . . 11 6.5. Advertising Leaf INFO Extended LSPs . . . . . . . . . . . . 12 7. Security Considerations. . . . . . . . . . . . . . . . . . . . 13 8. IANA Considerations. . . . . . . . . . . . . . . . . . . . . . 13 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14 9.1. Normative References. . . . . . . . . . . . . . . . . . . . 14 9.2. Informative References. . . . . . . . . . . . . . . . . . . 14 10. Authors' Addresses. . . . . . . . . . . . . . . . . . . . . . 15 McPherson, et al. [Page 3] INTERNET-DRAFT Expires: December 2008 June 2008 1. Overview [IS-IS] defines the set of LSP fragments which may be originated by a system at each level. This set is limited to 256 fragments. [IS- IS] also defines a maximum value for an LSP fragment (originatingLxLSPBufferSize) as 1492 bytes. The carrying capacity of an LSP set, while bounded, has thus far been sufficient for advertisements associated with an area/domain in existing deployment scenarios. However, the definition of additional information to be included in LSPs (e.g. multitopology support, traffic engineering information, router capabilities, etc.) has the potential to exceed the carrying capacity of an LSP set. This issue first drew interest when traffic engineering extensions were introduced. This interest resulted in the solution defined in RFC 3786. However, that solution suffers from restrictions required to maintain interoperability with systems which do not support the extensions. This document defines extensions which allow a system to exceed the 256 fragment limit and do so in a way which has no interoperability issues with systems which do not support the extension. It is seen as a simpler and therefore preferred solution to the problem. 2. Specification of Requirements 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 [RFC 2119]. 3. Definition of Commonly Used Terms This section provides definitions for terms that are used throughout the text. The terminology is consistent with that used in RFC 3786. Originating System: A physical IS running the IS-IS protocol. As this document describes a method which allows a single physical IS to originate LSPs on behalf of multiple virtual ISs, the Originating System represents the single physical IS. Normal system-id: The system-id of an Originating System as defined McPherson, et al. Section 3. [Page 4] INTERNET-DRAFT Expires: December 2008 June 2008 by [IS-IS]. Additional system-id: A system-id other than the "Normal system-id" that is assigned by the network administrator to an Originating System in order to allow the generation of extended LSP fragments. The Additional system-id, like the Normal system-id, must be unique throughout the routing area (Level-1) or domain (Level-2). Original LSP: An LSP using the Normal system-id in its LSP ID. Extended LSP: An LSP using an Additional system-id in its LSP ID. LSP set: Logical LSP. A group of LSP fragments (for a given level) which have the same LSPID. This term is used to resolve the ambiguity between a logical LSP and an LSP fragment, both of which are sometimes termed "LSP". Extended LSP set: An LSP set consisting of LSP fragments using an Additional system-id. Extension-capable IS: An IS implementing the mechanisms described in this document. 4. Utilizing Additional System IDs This extension allows an Originating System to be assigned additional system-ids which may be used to generate additional LSP sets. The additional system-ids are subject to the same restrictions as normal system-ids i.e. when used at Level-1 the additional system-id MUST be unique within the Level-1 area. When used at Level-2 the additional system-id MUST be unique within the domain. Extended LSPs are treated by the IS-IS Update Process in the same manner as normal LSPs i.e. the same rules as to generation, flooding, purging, etc. apply. In particular, if the Extended LSP with LSP Number zero and remaining lifetime > 0 is not present for a particular additional system-id then none of the extended LSPs in that Extended LSP set shall be processed. 4.1. Additional Information in Extended LSPs Fragment 0 of an Extended LSP Set MUST include the new IS alias ID McPherson, et al. Section 4.1. [Page 5] INTERNET-DRAFT Expires: December 2008 June 2008 TLV defined in Section 4.4. This allows the Extended LSP set to be associated with the Originating System which generated the LSP(s). 4.2. Extended LSP Restrictions The following restrictions on the information which may appear in an Extended LSP are defined in order to avoid interoperability issues with systems which do not support the extensions defined in this document. All TLV references are based on the current definitions in the IANA IS-IS TLV Codepoints Registry. 4.2.1. TLVs Which MUST NOT Appear The following TLVs MUST NOT appear in an Extended LSP: TLV Name (#) ----------- ES Neighbors (3) Part. DIS (4) Prefix Neighbors (5) If any of the TLVs listed above appear in an Extended LSP, an Extension Capable IS MUST ignore those TLVs on receipt and SHOULD report an error. Other TLVs in that extended LSP set MUST be processed normally. 4.2.2. Leaf Advertisements in Extended LSPs Advertisement of leaf information in Extended LSPs is allowed. Inclusion of such information requires the advertisement of a neighbor between the Originating System and the Virtual IS associated with the extended LSP set in which the leaf advertisements appear. See section 4.2.3. When leaf advertisements for multiple topologies (see [M-IS-IS]) are included in an Extended LSP set, the multi-topology TLV (229) MUST McPherson, et al. Section 4.2.2. [Page 6] INTERNET-DRAFT Expires: December 2008 June 2008 include all topologies for which a leaf advertisement is included. The following TLVs fall into this category: TLV Name (#) ----------- IP Int. Reach (128) IP Ext. Address (130) The extended IP reachability TLV (135) MT IP Reach (235) IPv6 IP Reach (236) MT IPv6 IP Reach (237) 4.2.3. IS Neigbor Advertisement Restrictions Advertisement of IS Neighbor Reachability in an Extended LSP is restricted to advertisement of neighbor reachability to the Originating System. A neighbor to the Originating System MUST be advertised in Extended LSPs. If multi-topology capability [M-IS-IS] is supported, an MT IS Neighbor advertisement to the Originating System IS MUST be included for every topology advertised in the Extended LSP set. Neighbor advertisement(s) to the Originating System in an Extended LSP MUST use a non-zero metric and SHOULD use a metric of MaxLinkMetric-1. The restrictions defined here apply to all TLVs used to advertise neighbor reachability. These include the following TLVs: TLV Name (#) ----------- IS Neighbors (2) The extended IS reachability TLV (22) MT-ISN (222) McPherson, et al. Section 4.2.3. [Page 7] INTERNET-DRAFT Expires: December 2008 June 2008 4.2.4. Area Adresses Fragment #0 of an Extended LSP set MUST include an Area Address TLV. The set of area addresses advertised MUST be a subset of the set of Area Addresses advertised in the normal LSP fragment #0 at the corresponding level. Preferably the advertisement SHOULD be syntactically identical to that included in the normal LSP fragment #0 at the corresponding level. 4.2.5. Overload, Attached, Partition Repair Bits The Overload (OL), Attached (ATT), and Partition Repair (P) bits MUST be set to 0 in all Extended LSP fragments. Note that ISs NOT supporting these extensions will interpret these bits normally in Extended LSPs they receive. If the ATT bit were set in an Extended LSP this could indicate that the Virtual IS is attached to other areas when the Originating System is not. This might cause legacy systems to use the Virtual IS as a default exit point from the area. 4.3. Originating LSP Requirements The Original LSP set MUST include a neighbor to the Virtual IS associated with each Extended LSP set generated. If multi-topology capability [M-IS-IS] is supported, an MT IS Neighbor advertisement to the Virtual IS MUST be included for every topology advertised in the Extended LSP set. The neighbor advertisement(s) in the Original LSP MUST specify a metric of zero. This guarantees that the two way connectivity check between Originating System and Virtual IS will succeed and that the cost of reaching the Virtual IS is the same as the cost to reach the Originating System. 4.4. IS Alias ID TLV (IS-Alias) The IS-Alias TLV allows extension-capable ISs to recognize the Originating System of an Extended LSP set. It identifies the Normal system-id of the Originating System. McPherson, et al. Section 4.4. [Page 8] INTERNET-DRAFT Expires: December 2008 June 2008 Type 24 Length # of octets in the value field (7 to 255) Value No. of octets +-----------------------+ | Normal System-id | 6 +-----------------------+ | Sub-TLV length | 1 +-----------------------+ | Sub-TLVs (optional) | 0 to 248 +-----------------------+ Normal system-id The Normal system-id of the Originating System Sub-TLVs length Total length of all sub-TLVs. Sub-TLVs No subTLVs are defined in this document. Should future extensions define subTLVs, the subTLVs MUST be formatted as described in RFC 3784. 4.5. New TLVs in Support of IS Neighbor Attributes One of the major sources of additional information in LSPs is the subTLV information associated with the extended IS reachability TLV (22) and MT IS Neighbor TLV (222). This includes (but is not limited to) information required in support of Traffic Engineering (TE) as defined in RFC 3784 and RFC 4205. The restrictions defined in this document prohibit the presence of TLV 22 and/or TLV 222 in Extended LSPs except to advertise the neighbor relationship to the Originating System. In the event that there is a need to advertise in Extended LSPs such information associated with neighbors of the Originating System, it is necessary to define new TLVs to carry the subTLV information. Two new TLVs are therefore defined. McPherson, et al. Section 4.5. [Page 9] INTERNET-DRAFT Expires: December 2008 June 2008 1) IS Neighbor Attribute TLV (23). It is identical in format to the Extended IS Reachability TLV (22). 2) MT IS Neighbor Attribute TLV (223). It is identical in format to the MT IS Neighbor TLV (222). These new TLVs MAY be included in Original LSPs or Extended LSPs. Regardless of the type of LSP in which the TLVs appear, the information pertains to the neighbor relationship between the Originating System and the IS identified in the TLV. These TLVs MUST NOT be used to infer that a neighbor relationship exists in the absence of TLV 22 or TLV 222 (whichever applies) in the Originating LSP set for the specified neighbor. This restriction is necessary in order to maintain compatibility with systems which do not support these extensions. 5. Comparison with the RFC 3786 Solution This document utilizes the same basic mechanism (additional system- ids) as RFC 3786 to allow an originating system to generate more than 256 LSP fragments. It differs from RFC 3786 in that it restricts the content of Extended LSPs to information which does NOT impact the building of a Shortest Path Tree (SPT). Legacy IS-IS implementations which do not support the extensions defined in this document see the extended LSPs as information associated with a system which is reachable only via the Originating System. As no other systems are reachable via the Virtual ISs, the SPF calculation in legacy ISs is therefore consistent with that performed by extension capable ISs. There is therefore no need for the two different operating modes defined in RFC 3786. There is also no need for the special handling of the original LSP set and the extended LSP set(s) as a single Logical LSP during the SPF as specified in Section 5 of RFC 3786. 6. Deployment Considerations There are a number of deployment considerations which limit the usefulness of extended LSPs unless all systems are extension-capable ISs. McPherson, et al. Section 6. [Page 10] INTERNET-DRAFT Expires: December 2008 June 2008 6.1. Advertising New TLVs in Extended LSPs As extended LSPs MAY be utilized to advertise TLVs associated with other protocol extensions (definition of which is outside the scope of this document) and/or the extensions defined in Section 4.4 of this document, it is obvious that the utilization of the information in extended LSPs by legacy IS-IS implementations will be limited. The implication of this is that as implementations are revised to support the protocol extensions which define new TLVs/subTLVs that MAY be advertised in extended LSPs, the implementation SHOULD also be revised to support the extensions defined in this document so that it is capable of processing the new information whether it appears in normal or extended LSPs. 6.2. Reachability and non-SPF TLV Staleness In cases where non-SPF information is advertised in LSPs, it is necessary to determine whether the system which originated the advertisement is reachable in order to guarantee that a receiving IS does not use or leak stale information. As long as the OL bit is NOT set by the Originating System in normal LSPs, reachability to the Virtual IS will be consistent with reachability to the Originating System. Therefore, no special rules are required in this case. 6.3. Normal LSP OL State and Use of Extended LSPs If the Originating System sets the OL bit in a normal LSP, legacy systems will see the Virtual ISs associated with that Originating System as unreachable and therefore will not use the information in the corresponding Extended LSPs. Under these circumstances, Extension capable ISs MUST also see the Virtual ISs as unreachable. This avoids potential routing loops in cases where leaf information is advertised in Extended LSPs. 6.4. Moving Neighbor Attribute INFO LSPs Section 4.4 defines new TLVs which MAY be used to advertise neighbor attribute information in extended LSPs. In cases where neighbor McPherson, et al. Section 6.4. [Page 11] INTERNET-DRAFT Expires: December 2008 June 2008 attribute information associated with the same context (e.g. the same link) appears in both an Original LSP and in one or more Extended LSP Sets, the following rules apply for each attribute: o If the attribute information does not conflict, it MUST be considered additive o If the attribute information conflicts, then the information in the Original LSP, if present, MUST be used. If no information is in the Original LSP, then the information from the Extended LSP with the lowest system-id SHALL be preferred. o In cases where information about the same neighbor/link/attribute appears in both TLV 22 and TLV 23 (or TLV 222 and TLV 223 for the same MTID) then the information in TLV 22 (or TLV 222) MUST be used and the information in TLV 23 (or TLV 223) MUST be ignored. Utilization of the new TLVs for neighbor attribute information would provide additional benefits which include: o Elimination of the need for redundant IS neighbor TLVs to be processed as part of the SPF. o Easier support for a set of TE information associated with a single link which exceeds the 255 byte TLV limit by allowing the interpretation of multiple TLVs to be considered additive rather than mutually exclusive. 6.5. Advertising Leaf INFO Extended LSPs The need to advertise leaf information in Extended LSPs may arise because of extensive leaking of inter-level information or because of the support of multiple topologies as described in [M-IS-IS]. When leaf information is advertised in Extended LSPs, these LSPs now contain information which MUST be processed in order to correctly update the forwarding plane of an IS. This may increase the frequency of events which trigger forwarding plane updates by ISs in the network. It is therefore recommended that, when possible, leaf information be restricted to the normal LSP set. McPherson, et al. Section 6.5. [Page 12] INTERNET-DRAFT Expires: December 2008 June 2008 7. Security Considerations This document raises no new security issues for IS-IS. 8. IANA Considerations This document defines the following new ISIS TLVs that need to be reflected in the ISIS TLV code-point registry: Type Description IIH LSP SNP ---- ----------------------------------- --- --- --- 23 IS Neighbor Attribute n y n 24 IS Alias ID n y n 223 MT IS Neighbor Attribute n y n McPherson, et al. Section 8. [Page 13] INTERNET-DRAFT Expires: December 2008 June 2008 9. References 9.1. 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. [RFC 3784] Smit, H. and T. Li, "Intermediate System to Intermediate System (IS-IS) Extensions for Traffic Engineering (TE)", RFC 3784, June 2004. [RFC 3786] Hermelin, A., Previdi, S. and Shand, M., "Extending the Number of Intermediate to Intermediate (IS-IS) Link State PDU (LSP) Fragments Beyond the 256 Limit," RFC 3786, May 2004. [RFC 4205] Kompella, K. and Rehkter, Y., "Intermediate System to Intermediate System (IS-IS) Extensions in Support of Generalized Multi-Protocol Label Switching (GMPLS)", RFC 4205, October 2005. [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 9.2. Informative References [M-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. McPherson, et al. Section 9.2. [Page 14] INTERNET-DRAFT Expires: December 2008 June 2008 10. Authors' Addresses Les Ginsberg Cisco Systems Email: ginsberg@cisco.com Stefano Previdi Cisco Systems Email: sprevidi@cisco.com Mike Shand Cisco Systems Email: mshand@cisco.com Danny McPherson Arbor Networks, Inc. Email: danny@arbor.net Intellectual Property Statement 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. McPherson, et al. Section 10. [Page 15] INTERNET-DRAFT Expires: December 2008 June 2008 Copyright Statement Copyright (C) The IETF Trust (2008). 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, THE IETF TRUST 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. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). McPherson, et al. Section 10. [Page 16]