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Network Working Group                                  D. McPherson, Ed.Request for Comments: 5311                                Arbor NetworksObsoletes:3786                                              L. Ginsberg                                                              S. Previdi                                                                M. Shand                                                           Cisco Systems                                                           February 2009Simplified Extension of Link State PDU (LSP) Space for IS-ISStatus of This Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Copyright Notice   Copyright (c) 2009 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document.   Please review these documents carefully, as they describe your rights   and restrictions with respect to this document.Abstract   This document describes a simplified method for extending the Link   State PDU (LSP) space beyond the 256 LSP limit.  This method is   intended as a preferred replacement for the method defined inRFC3786.McPherson, et al.           Standards Track                     [Page 1]

RFC 5311      Simplified Extension of LSP Space for IS-IS  February 2009Table of Contents1. Overview ........................................................22. Specification of Requirements ...................................33. Definition of Commonly Used Terms ...............................34. Utilizing Additional System IDs .................................44.1. Additional Information in Extended LSPs ....................44.2. Extended LSP Restrictions ..................................44.2.1. TLVs That MUST NOT Appear ...........................44.2.2. Leaf Advertisements in Extended LSPs ................54.2.3. IS Neighbor Advertisement Restrictions ..............54.2.4. Area Addresses ......................................64.2.5. Overload, Attached, Partition Repair Bits ...........64.3. Originating LSP Requirements ...............................64.4. IS Alias ID TLV (IS Alias ID) ..............................74.5. New TLVs in Support of IS Neighbor Attributes ..............75. Comparison with theRFC 3786 Solution ...........................86. Deployment Considerations .......................................86.1. Advertising New TLVs in Extended LSPs ......................96.2. Reachability and Non-SPF TLV Staleness .....................96.3. Normal LSP OL State and Use of Extended LSPs ...............96.4. Moving Neighbor Attribute INFO LSPs ........................96.5. Advertising Leaf INFO Extended LSPs .......................107. Security Considerations ........................................108. IANA Considerations ............................................109. References .....................................................119.1. Normative References ......................................119.2. Informative References ....................................111.  Overview   [IS-IS] defines the set of LSPs that may be originated by a system at   each level.  This set is limited to 256 LSPs.  [IS-IS] also defines a   maximum value for an LSP (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., multi-topology 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   [RFC3786].  However, that solution suffers from restrictions required   to maintain interoperability with systems that do not support the   extensions.McPherson, et al.           Standards Track                     [Page 2]

RFC 5311      Simplified Extension of LSP Space for IS-IS  February 2009   This document defines extensions that allow a system to exceed the   256 LSP limit and do so in a way that has no interoperability issues   with systems that 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 inRFC 2119 [BCP14].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 inRFC 3786.   Originating System: A physical IS running the IS-IS protocol.  As   this document describes a method that 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   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 LSPs.  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: All LSPs of a given level having the same system ID and   Pseudonode ID.  (The LSPID field then only varies in the LSP number   octet.) This constitutes the complete set of link state information   at a given level originated using that system ID/Pseudonode ID.  This   term is defined to resolve the ambiguity between a logical LSP and a   single Link State PDU -- which is sometimes called an LSP fragment.   The latter is the unit of information handled by the update process.   Extended LSP set: An LSP set consisting of LSPs using an Additional   system-id.   Extension-capable IS: An IS implementing the mechanisms described in   this document.McPherson, et al.           Standards Track                     [Page 3]

RFC 5311      Simplified Extension of LSP Space for IS-IS  February 2009   Virtual IS: The system, identified by an Additional system-id,   advertised as originating the Extended LSPs.  These LSPs specify the   Additional system-id in their LSP IDs.4.  Utilizing Additional System IDs   This extension allows an Originating System to be assigned additional   system-ids that 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   The LSP number zero of an Extended LSP set MUST include the new IS   alias ID TLV defined inSection 4.4.  This allows the Extended LSP   set to be associated with the Originating System that generated the   LSP(s).4.2.  Extended LSP Restrictions   The following restrictions on the information that may appear in an   Extended LSP are defined in order to avoid interoperability issues   with systems that 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 That MUST NOT Appear   The following TLVs MUST NOT appear in an Extended LSP:      TLV Name (#)      -----------      ES Neighbors (3)      Part. DIS (4)      Prefix Neighbors (5)McPherson, et al.           Standards Track                     [Page 4]

RFC 5311      Simplified Extension of LSP Space for IS-IS  February 2009   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.   SeeSection 4.2.3.   When leaf advertisements for multiple topologies (see [RFC5120]) are   included in an Extended LSP set, the multi-topology TLV (229) MUST   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 Neighbor 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 [RFC5120]   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 (#)      -----------      IIS Neighbors (2)      The extended IS reachability TLV (22)      MT-ISN (222)McPherson, et al.           Standards Track                     [Page 5]

RFC 5311      Simplified Extension of LSP Space for IS-IS  February 20094.2.4.  Area Addresses   LSP number zero 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 number zero at the   corresponding level.  Preferably, the advertisement SHOULD be   syntactically identical to that included in the normal LSP number   zero 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 LSPs.   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 [RFC5120] 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.McPherson, et al.           Standards Track                     [Page 6]

RFC 5311      Simplified Extension of LSP Space for IS-IS  February 20094.4.  IS Alias ID TLV (IS Alias ID)   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.      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 sub-TLVs are defined in this document.  Should future      extensions define sub-TLVs, the sub-TLVs MUST be formatted as      described in [RFC5305].4.5.  New TLVs in Support of IS Neighbor Attributes   One of the major sources of additional information in LSPs is the   sub-TLV information associated with the extended IS reachability TLV   (22) and MT-ISN TLV (222).  This includes (but is not limited to)   information required in support of Traffic Engineering (TE) as   defined in [RFC5305] and [RFC5307].  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 sub-TLV   information.McPherson, et al.           Standards Track                     [Page 7]

RFC 5311      Simplified Extension of LSP Space for IS-IS  February 2009   Two new TLVs are therefore defined.   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-ISN 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 that do not   support these extensions.5.  Comparison with theRFC 3786 Solution   This document utilizes the same basic mechanism (additional system-   ids) asRFC 3786 to allow an originating system to generate more than   256 LSPs.  It differs fromRFC 3786 in that it restricts the content   of Extended LSPs to information that 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 that is reachable only via the Originating   System.  As no other systems are reachable via the Virtual ISs, the   Shortest Path First (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 inRFC 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 inSection 5 of RFC 3786.6.  Deployment Considerations   There are a number of deployment considerations that limit the   usefulness of Extended LSPs unless all systems are extension-capable   ISs.McPherson, et al.           Standards Track                     [Page 8]

RFC 5311      Simplified Extension of LSP Space for IS-IS  February 20096.1.  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 inSection 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 that define new TLVs/sub-TLVs 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 that 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 LSPsSection 4.4 defines new TLVs that MAY be used to advertise neighbor   attribute information in Extended LSPs.  In cases where neighbor   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 isMcPherson, et al.           Standards Track                     [Page 9]

RFC 5311      Simplified Extension of LSP Space for IS-IS  February 2009     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 that 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 that 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 [RFC5120].     When leaf information is advertised in Extended LSPs, these LSPs     now contain information that MUST be processed in order to     correctly update the forwarding plane of an IS.  This may increase     the frequency of events that 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.7.  Security Considerations     This document raises no new security issues for IS-IS.  For general     security considerations for IS-IS, see [RFC5304].8.  IANA Considerations     This document defines the following new ISIS TLVs that are     reflected in the ISIS TLV codepoint 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     nMcPherson, et al.           Standards Track                    [Page 10]

RFC 5311      Simplified Extension of LSP Space for IS-IS  February 20099.  References9.1.  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.   [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic             Engineering",RFC 5305, October 2008.   [RFC5307] Kompella, K., Ed., and Y. Rekhter, Ed., "IS-IS Extensions             in Support of Generalized Multi-Protocol Label Switching             (GMPLS)",RFC 5307, October 2008.   [BCP14]   Bradner, S., "Key words for use in RFCs to Indicate             Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi             Topology (MT) Routing in Intermediate System to             Intermediate Systems (IS-ISs)",RFC 5120, February 2008.9.2.  Informative References   [RFC3786] Hermelin, A., Previdi, S., and M. Shand, "Extending the             Number of Intermediate System to Intermediate System (IS-             IS) Link State PDU (LSP) Fragments Beyond the 256 Limit",RFC 3786, May 2004.   [RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic             Authentication",RFC 5304, October 2008.McPherson, et al.           Standards Track                    [Page 11]

RFC 5311      Simplified Extension of LSP Space for IS-IS  February 2009Authors' Addresses   Danny McPherson (editor)   Arbor Networks, Inc.   EMail:  danny@arbor.net   Les Ginsberg   Cisco Systems   EMail: ginsberg@cisco.com   Stefano Previdi   Cisco Systems   EMail: sprevidi@cisco.com   Mike Shand   Cisco Systems   EMail: mshand@cisco.comMcPherson, et al.           Standards Track                    [Page 12]