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Versions: 00 01 02 03 04 05 06 07 rfc4971                               
draft-ietf-isis-caps-00.txt                               January 2005
  Internet Draft                         Jean-Philippe Vasseur(Ed)
                                              Cisco Systems, Inc.
                                              Rahul Aggarwal(Ed)
                                                Juniper Networks
                                                Naiming Shen(Ed)
                                                Redback Networks

  Expires: July 2005                                 January 2005

          IS-IS extensions for advertising router information


Status of this Memo

  By submitting this Internet-Draft, I certify that any applicable
  patent or IPR claims of which I am aware have been disclosed, and any
  of which I become aware will be disclosed, in accordance with RFC

  This document is an Internet-Draft and is in full conformance with
  all provisions of Section 10 of RFC2026 [i].

  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-

  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 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.

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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 [ii].

Table of Contents

  1. Introduction............................................2
  2. IS-IS Router CAPABILITY TLV.............................3
  3. Element of procedure....................................4
  4. Interoperability with routers not supporting the
     capability TLV..........................................5
  5. Security considerations.................................5
  6. Acknowledgment..........................................5
  7. Intellectual Property Considerations....................5
  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
    routers to learn the capabilities of the other routers of their IS-
    IS level, area or routing domain. Some applications are described
    in [IS-IS-TE-CAP]. 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 requires some
    significant configuration effort. [IS-IS-TE-CAP] 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 ([IS-
    IS-TE]) allows an LSR to advertise its Point To Multipoint
    capabilities ([P2MP] and [P2MP-REQS]).

  The use of ISIS 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

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  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.


  The IS-IS Router CAPABILITY TLV is composed of 1 octet for the type,
  1 octet specifying the TLV length, 1 octet of bit flags 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.

  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

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3. Elements of procedure

  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
  MUST 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 MUST 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 MUST be leaked
    into other IS-IS levels. When the TLV is leaked from level-2 to
    level-1, the D bit MUST be set in the level-1 LSP advertisement.

  When leaking Capability TLVs downward from Level-2 into Level-1, if
  the originator of the TLV is a Level-1 router in another area, it is
  possible that multiple copies of the same TLV may be received from
  multiple L2 routers in the originating area. To prevent a router from
  leaking multiple copies of the same TLV, the router performing the
  downward leaking MUST check for such duplication by comparing the
  contents of the TLVs.

  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

  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
  capabilities TLV in the same LSP fragment as the advertisement which

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  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

  No new security issues are raised in this document.

6. Acknowledgments

  The authors would like to thank Jean-Louis Le Roux, Paul Mabey and
  Andrew Partan for their useful comments.

7. 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

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  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-

8. References

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., "Use of OSI IS-IS for routing in TCP/IP and
  dual environments", RFC 1195, December 1990.

  [ISIS-TE] Li, T., Smit, H., "IS-IS extensions for Traffic
  Engineering", RFC 3784, June 2004.

Informative references

  [IS-IS-TE-CAP] JP Vasseur, S. Previdi, Paul Mabey and JL. Le Roux,
  ôIS-IS MPLS Traffic Engineering capabilitiesö, draft-vasseur-isis-te-
  caps-00.txt, 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-00.txt, work in progress.

  [P2MP-REQS] S. Yasukawa et al. ½ Requirements for point to multipoint
  extension to RSVP ©, draft-ietf-mpls-p2mp-sig-requirement-00.txt,
  work in progress.

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9. Author's Addresses

  Jean-Philippe Vasseur
  CISCO Systems, Inc.
  300 Beaver Brook
  Boxborough, MA 01719
  Email: jpv@cisco.com

  Stefano Previdi
  CISCO Systems, Inc.
  Via Del Serafico 200
  00142 - Roma
  Email: sprevidi@cisco.com

  Mike Shand
  Cisco Systems
  250 Longwater Avenue,
  RG2 6GB
  Email: mshand@cisco.com

  Les Ginsberg
  Cisco Systems
  510 McCarthy Blvd.
  Milpitas, Ca. 95035 USA
  Email: ginsberg@cisco.com

  Acee Lindem
  Cisco Systems
  7025 Kit Creek Road
  Research Triangle Park, NC 27709
  e-mail: acee@cisco.com

  Naiming Shen
  Cisco Systems
  225 West Tasman Drive
  San Jose, CA 95134
  e-mail: naiming@cisco.com

  Rahul Aggarwal
  Juniper Networks
  1194 N. Mathilda Avenue
  San Jose, CA 94089

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  e-mail: rahul@juniper.net

  Scott Shaffer
  e-mail: sshaffer@bridgeport-networks.com

  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

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