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Intermediate System to Intermediate System (IS-IS) Extensions for Advertising Router Information

The information below is for an old version of the document that is already published as an RFC.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 4971.
Authors JP Vasseur , Naiming Shen , Rahul Aggarwal
Last updated 2015-10-14 (Latest revision 2007-02-15)
RFC stream Internet Engineering Task Force (IETF)
Intended RFC status Proposed Standard
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IESG IESG state Became RFC 4971 (Proposed Standard)
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Responsible AD Bill Fenner (ˢˣˠ)
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Network Working Group                         Jean-Philippe Vasseur(Ed)
Internet Draft                                        Naiming Shen (Ed)
Proposed status: Standard                           Cisco Systems, Inc.
Expires: August 2007                                 Rahul Aggarwal(Ed)
                                                       Juniper Networks

                                                          February 2007

            IS-IS Extensions for Advertising Router Information 


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 
   The list of Internet-Draft Shadow Directories can be accessed at 

   This Internet-Draft will expire on August 15, 2007.
   This document defines a new optional IS-IS TLV named CAPABILITY, 
   formed of multiple sub-TLVs, which allows a router to announce its 
   capabilities within an IS-IS level or the entire routing domain. 
Conventions used in this document 
   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 
   document are to be interpreted as described in RFC-2119 [RFC-2119]. 

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Table of Contents 
   1. Introduction...................................................2 
   2. IS-IS Router CAPABILITY TLV....................................3 
   3. Element of procedure...........................................3 
   4. Interoperability with routers not supporting the capability TLV.5 
   5. Security considerations........................................5   
   6. Acknowledgment.................................................6 
   7. Intellectual Property Considerations...........................6 
   8. References.....................................................6 
   Normative references..............................................6 
   Informative references............................................6  
   9. Author's Addresses.............................................7 
1. Introduction 
     There are several situations where it is useful for the IS-IS
     [IS-IS, IS-IS-IP] routers to learn the capabilities of the other
     routers of their IS-IS level, area or routing domain. For the sake
     of illustration, two examples related to MPLS Traffic Engineering
     are described here:
     1. Mesh-group: the setting up of a mesh of TE LSPs [IS-IS-TE]
     requires some significant configuration effort. [AUTOMESH]
     proposes an auto-discovery mechanism whereby every LSR of a mesh
     advertises its mesh-group membership by means of IS-IS extensions.
     2. Point to Multi-point TE LSP (P2MP LSP). A specific sub-TLV ([TE-
     NODE-CAP]) allows an LSR to advertise its Point To Multipoint 
     capabilities ([P2MP] and [P2MP-REQS]). 

     3. Inter-area traffic engineering: Advertisement of the IPv4
     and/or the IPv6 Traffic Engineering Router IDs.
   The use of IS-IS for Path Computation Element (PCE) discovery may 
   also be considered and will be discussed in the PCE WG. 
   The capabilities mentioned above require the specification of new 
   sub-TLVs carried within the CAPABILITY TLV defined in this document. 
   Note that the examples above are provided for the sake of 
   illustration. This document proposes a generic capability advertising 
   mechanism not limited to MPLS Traffic Engineering. 
   This document defines a new optional IS-IS TLV named CAPABILITY, 
   formed of multiple sub-TLVs, which allows a router to announce its 
   capabilities within an IS-IS level or the entire routing domain. The 
   applications mentioned above require the specification of new sub-
   TLVs carried within the CAPABILITY TLV defined in this document. 
   Definition of these sub-TLVs is outside the scope of this document. 
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   The IS-IS Router CAPABILITY TLV is composed of 1 octet for the type, 
   1 octet specifying the number of bytes in the value field, and a 
   variable length value field, starting with 4 octets of Router ID, 
   indicating the source of the TLV, and followed by 1 octet of flags. 
   A set of optional sub-TLVs may follow the flag field. Sub-TLVs are
   formatted as described in RFC 3784 [IS-IS-TE].
   TYPE: 242 (To be assigned by IANA) 
   LENGTH: from 5 to 255 
     Router ID (4 octets) 
     Flags (1 octet) 
     Set of optional sub-TLVs (0-250 octets) 
             0 1 2 3 4 5 6 7 
             | Reserved  |D|S| 
   Currently two bit flags are defined. 
   S bit (0x01): If the S bit is set(1), the IS-IS Router CAPABILITY TLV 
   MUST be flooded across the entire routing domain. If the S bit is not 
   set(0), the TLV MUST NOT be leaked between levels. This bit MUST NOT 
   be altered during the TLV leaking. 
   D bit (0x02): When the IS-IS Router CAPABILITY TLV is leaked from 
   level-2 to level-1, the D bit MUST be set. Otherwise this bit MUST be 
   clear. IS-IS Router capability TLVs with the D bit set MUST NOT be 
   leaked from level-1 to level-2. This is to prevent TLV looping. 
   The Router CAPABILITY TLV is OPTIONAL. As specified in section 3, 
   more than one Router CAPABILITY TLVs from the same source MAY be 
   This document does not specify how an application may use the Router 
   Capability TLV and such specification is outside the scope of this 
3. Elements of procedure 
   A router which generates a CAPABILITY TLV MUST have a Router ID
   which is a 32 bit number. The ID MUST be unique within the IS-IS
   area. If the router generates any capability TLVs with domain
   flooding scope then the ID MUST also be unique within the IS-IS
   routing domain.

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   When advertising capabilities with different flooding scopes, a 
   router MUST originate a minimum of two Router CAPABILITY TLVs, each 
   TLV carrying the set of sub-TLVs with the same flooding scope. For 
   instance, if a router advertises two sets of capabilities C1 and C2 
   with an area/level scope and routing domain scope respectively, C1 
   and C2 being specified by their respective sub-TLV(s), the router 
   will originate two Router CAPABILITY TLVs: 
      - One Router CAPABILITY TLV with the S flag cleared, carrying the 
     sub-TLV(s) relative to C1. This Router CAPABILITY TLV will not be 
     leaked into another level. 
      - One Router CAPABILITY TLV with the S flag set, carrying the sub-
     TLV(s) relative to C2. This Router CAPABILITY TLV will be leaked 
     into other IS-IS levels. When the TLV is leaked from level-2 to 
     level-1, the D bit will be set in the level-1 LSP advertisement. 
   In order to prevent the use of stale capabilities information A 
   system MUST NOT use a Capability TLV present in an LSP of a system 
   which is not currently reachable via Level-x paths, where "x" is the 
   level (1 or 2) in which the sending system advertised the TLV. This 
   requirement applies regardless of whether the sending system is the 
   originator of the Capabilities TLV or not. Note that leaking a 
   Capabilities TLV is one of the uses which is prohibited under these 
   Example: If Level-1 router A generates a Capability TLV and floods 
   it to two L1/L2 routers S and T, they will flood it into the Level-2 
   domain. Now suppose the Level-1 area partitions, such that A and S 
   are in one partition and T is in another. IP routing will still 
   continue to work, but if A now issues a revised version of the CAP 
   TLV, or decides to stop advertising it, S will follow suit, but T 
   will continue to advertise the old version until the LSP times out. 
   Routers in other areas have to choose whether to trust T's copy of 
   A's capabilities or S's copy of A's information and they have no 
   reliable way to choose. By making sure that T stops leaking A's 
   information, this removes the possibility that other routers will 
   use stale information from A. 
   In IS-IS, the atomic unit of the update process is a TLV - or more 
   precisely in the case of TLVs which allow multiple entries to appear 
   in the value field (e.g. IS-neighbors) - an entry in the value field 
   of a TLV. If an update to an entry in a TLV is advertised in an LSP 
   fragment different from the LSP fragment associated with the old 
   advertisement, the possibility exists that other systems can 
   temporarily have either 0 copies of a particular advertisement or 2 
   copies of a particular advertisement, depending on the order in which 
   new copies of the LSP fragment which had the old advertisement and 
   the fragment which has the new advertisement arrive at other systems. 
   Wherever possible, an implementation SHOULD advertise the update to a 

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   capabilities TLV in the same LSP fragment as the advertisement which 
   it replaces. Where this is not possible, the two affected LSP 
   fragments should be flooded as an atomic action. 
   Systems which receive an update to an existing capability TLV can 
   minimize the potential disruption associated with the update by 
   employing a holddown time prior to processing the update so as to 
   allow for the receipt of multiple LSP fragments associated with the 
   same update prior to beginning processing. 
   Where a receiving system has two copies of a capabilities TLV from 
   the same system which have different settings for a given attribute, 
   the procedure used to choose which copy shall be used is undefined. 
4. Interoperability with routers not supporting the capability TLV. 
   Routers which do not support the Router CAPABILITY TLV MUST silently 
   ignore the TLV(s) and continue processing other TLVs in the same LSP. 
   Routers which do not support specific sub-TLVs carried within a 
   Router CAPABILITY TLV MUST silently ignore the unsupported sub-TLVs 
   and continue processing those sub-TLVs in the Router CAPABILITY TLV 
   which are supported. How partial support may impact the operation of 
   the capabilities advertised within the Router CAPABILITY TLV is 
   outside the scope of this document. 
   In order for Router CAPABILITY TLVs with domain-wide scope originated 
   by L1 Routers to be flooded across the entire domain at least one 
   L1/L2 Router in every area of the domain MUST support the Router 
   If leaking of the CAP TLV is required, the entire CAP TLV MUST be 
   leaked into another level even though it may contain some of the 
   unsupported sub-TLVs. 
5. Security considerations 
   Any new security issues raised by the procedures in this document
   depend upon the opportunity for LSPs to be snooped and modified,
   the ease/difficulty of which has not been altered. As the LSPs may
   now contain additional information regarding router capabilities,
   this new information would also become available to an attacker.
   Specifications based on this mechanism need to describe the
   security considerations around the disclosure and modification
   of their information. Note that an integrity mechanism, such as
   one defined in RFC3567 or draft-ietf-isis-hmac-sha, should be
   applied if there is high risk resulting from modification of
   capability information.

6. IANA considerations 
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   IANA will assign a new IS-IS TLV code-point for the newly defined IS-
   IS TLV type named the IS-IS Router CAPABILITY TLV and defined in this 
   document. Suggested value is 242 (to be assigned by IANA). 
7. Acknowledgment 
   The authors would like to thank Jean-Louis Le Roux, Paul Mabey, 
   Andrew Partan and Adrian Farrel for their useful comments. 
8. Intellectual Property Considerations 
   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 
   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- 
9. References 
9.1 Normative references 
   [RFC-2119] 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., "Use of OSI IS-IS for routing in TCP/IP and 
       dual environments", RFC 1195, December 1990. 
   [IS-IS-TE] Li, T., Smit, H., "IS-IS extensions for Traffic
       Engineering", RFC 3784, June 2004. 

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9.2 Informative references 

   [AUTOMESH] JP Vasseur, JL. Le Roux et al, "Routing extensions for 
   discovery of Multiprotocol (MPLS) Label Switch Router (LSR) Traffic 
   Engineering (TE) mesh membership", draft-ietf-ccamp-automesh, work in 
   [TE-NODE-CAP] JP Vasseur, JL. Le Roux et al, "Routing extensions for 
   discovery of Traffic Engineering Node Capabilities", draft-ietf-
   ccamp-te-node-cap, work in progress. 
   [P2MP] R. Aggarwal,D. Papadimitriou,S. Yasukawa, et. al. "Extensions 
   to RSVP-TE for Point To Multipoint TE LSPs", draft-ietf-mpls-rsvp-te-
   p2mp, work in progress.  
   [P2MP-REQS] S. Yasukawa et al. "Requirements for point to multipoint 
   extension to RSVP", draft-ietf-mpls-p2mp-sig-requirement, work in 
10. Authors' Addresses 
   Jean-Philippe Vasseur 
   CISCO Systems, Inc. 
   1414 Massachusetts Avenue 
   Boxborough, MA 01719 
   Stefano Previdi 
   CISCO Systems, Inc. 
   Via Del Serafico 200 
   00142 - Roma 
   Mike Shand  
   Cisco Systems  
   250 Longwater Avenue,  
   RG2 6GB  
   Les Ginsberg  
   Cisco Systems  
   510 McCarthy Blvd.  
   Milpitas, Ca. 95035 USA  

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   Acee Lindem 
   Redback Networks
   102 Carric Bend Court
   Cary, NC 27519
   Naiming Shen 
   Cisco Systems 
   225 West Tasman Drive 
   San Jose, CA 95134 
   Rahul Aggarwal 
   Juniper Networks 
   1194 N. Mathilda Avenue 
   San Jose, CA 94089 
   Scott Shaffer 
Full Copyright Statement 
   Copyright (C) The IETF Trust (2007). 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


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