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IS-IS Extensions for Advertising Router Info

The information below is for an old version of the document.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 7981.
Authors Les Ginsberg , Stefano Previdi , Mach Chen
Last updated 2016-03-01 (Latest revision 2016-01-29)
Replaces draft-ginsberg-isis-rfc4971bis
RFC stream Internet Engineering Task Force (IETF)
Additional resources Mailing list discussion
Stream WG state In WG Last Call
Document shepherd Christian Hopps
IESG IESG state I-D Exists
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Responsible AD (None)
Send notices to "Christian Hopps" <>
Networking Working Group                                     L. Ginsberg
Internet-Draft                                                S. Previdi
Intended status: Standards Track                           Cisco Systems
Expires: August 1, 2016                                          M. Chen
                                            Huawei Technologies Co., Ltd
                                                        January 29, 2016

              IS-IS Extensions for Advertising Router Info


   This document defines a new optional Intermediate System to
   Intermediate System (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.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at

   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."

   This Internet-Draft will expire on August 1, 2016.

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents

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   ( 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.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  IS-IS Router CAPABILITY TLV . . . . . . . . . . . . . . . . .   3
   3.  Elements of Procedure . . . . . . . . . . . . . . . . . . . .   4
   4.  Interoperability with Routers Not Supporting the Capability
       TLV . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     8.2.  Informational References  . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   There are several situations where it is useful for the IS-IS
   [ISO10589] [RFC1195] routers to learn the capabilities of the other
   routers of their IS-IS level, area, or routing domain.  For the sake
   of illustration, three examples related to MPLS Traffic Engineering
   (TE) are described here:

   1.  Mesh-group: the setting up of a mesh of TE Label Switched Paths
       (LSPs) [RFC5305] requires some significant configuration effort.
       [RFC4972] proposes an auto-discovery mechanism whereby every
       Label Switching Router (LSR) of a mesh advertises its mesh-group
       membership by means of IS-IS extensions.

   2.  Point to Multipoint TE LSP (RFC4875).  A specific sub-TLV
       [RFC5073] allows an LSR to advertise its Point To Multipoint
       capabilities ([RFC4875] and [RFC4461]).

   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.

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   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 that is not limited to MPLS Traffic

   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.


   The IS-IS Router CAPABILITY TLV is composed of 1 octet for the type,
   1 octet that specifies the number of bytes in the value field, and a
   variable length value field that starts 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 [RFC5305].

    TYPE: 242
      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.

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   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 TLV 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

   The Router ID SHOULD be identical to the value advertised in the
   Traffic Engineering Router ID TLV [RFC5305].  If no Traffic
   Engineering Router ID is assigned the Router ID SHOULD be identical
   to an IP Interface Address [RFC1195] advertised by the originating
   IS.  If the originating node does not support IPv4, then the reserved
   value MUST be used in the Router ID field and the IPv6 TE
   Router ID sub-TLV [RFC5316] MUST be present in the TLV.  Router
   CAPABILITY TLVs which have a Router ID of and do NOT have the
   IPv6 TE Router ID sub-TLV present MUST be ignored.

   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, a system MUST NOT
   use a Capability TLV present in an LSP of a system that 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 or not the sending system is the

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   originator of the Capabilities TLV.  Note that leaking a Capabilities
   TLV is one of the uses that is prohibited under these conditions.

      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 that allow multiple entries to appear
   in the value field (e.g., IS-neighbors), the atomic unit is 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 that had the old
   advertisement and the fragment that 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 that
   it replaces.  Where this is not possible, the two affected LSP
   fragments should be flooded as an atomic action.

   Systems that 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 that have different settings for a given attribute,
   the procedure used to choose which copy shall be used is undefined.

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4.  Interoperability with Routers Not Supporting the Capability TLV

   Routers that do not support the Router CAPABILITY TLV MUST silently
   ignore the TLV(s) and continue processing other TLVs in the same LSP.
   Routers that 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 that are supported in the Router
   CAPABILITY TLV.  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 CAPABILITY TLV is required, the entire CAPABILITY
   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 the one
   defined in [RFC5304] or [RFC5310], should be applied if there is high
   risk resulting from modification of capability information.

6.  IANA Considerations

   IANA assigned 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.  The assigned value is 242.

7.  Acknowledgements

   For the original version of RFC 4971 the authors thanked Jean-Louis
   Le Roux, Paul Mabey, Andrew Partan, and Adrian Farrel for their
   useful comments.

   For this new version the authors would like to thank Kris Michielsen
   for calling the problem associated w an IPv6 only router to our

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8.  References

8.1.  Normative References

              International Organization for Standardization,
              "Intermediate system to Intermediate system intra-domain
              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, Nov 2002.

   [RFC1195]  Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
              dual environments", RFC 1195, DOI 10.17487/RFC1195,
              December 1990, <>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC5073]  Vasseur, J., Ed. and J. Le Roux, Ed., "IGP Routing
              Protocol Extensions for Discovery of Traffic Engineering
              Node Capabilities", RFC 5073, DOI 10.17487/RFC5073,
              December 2007, <>.

   [RFC5304]  Li, T. and R. Atkinson, "IS-IS Cryptographic
              Authentication", RFC 5304, DOI 10.17487/RFC5304, October
              2008, <>.

   [RFC5305]  Li, T. and H. Smit, "IS-IS Extensions for Traffic
              Engineering", RFC 5305, DOI 10.17487/RFC5305, October
              2008, <>.

   [RFC5310]  Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
              and M. Fanto, "IS-IS Generic Cryptographic
              Authentication", RFC 5310, DOI 10.17487/RFC5310, February
              2009, <>.

   [RFC5316]  Chen, M., Zhang, R., and X. Duan, "ISIS Extensions in
              Support of Inter-Autonomous System (AS) MPLS and GMPLS
              Traffic Engineering", RFC 5316, DOI 10.17487/RFC5316,
              December 2008, <>.

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8.2.  Informational References

   [RFC4461]  Yasukawa, S., Ed., "Signaling Requirements for Point-to-
              Multipoint Traffic-Engineered MPLS Label Switched Paths
              (LSPs)", RFC 4461, DOI 10.17487/RFC4461, April 2006,

   [RFC4875]  Aggarwal, R., Ed., Papadimitriou, D., Ed., and S.
              Yasukawa, Ed., "Extensions to Resource Reservation
              Protocol - Traffic Engineering (RSVP-TE) for Point-to-
              Multipoint TE Label Switched Paths (LSPs)", RFC 4875,
              DOI 10.17487/RFC4875, May 2007,

   [RFC4972]  Vasseur, JP., Ed., Leroux, JL., Ed., Yasukawa, S.,
              Previdi, S., Psenak, P., and P. Mabbey, "Routing
              Extensions for Discovery of Multiprotocol (MPLS) Label
              Switch Router (LSR) Traffic Engineering (TE) Mesh
              Membership", RFC 4972, DOI 10.17487/RFC4972, July 2007,

Authors' Addresses

   Les Ginsberg
   Cisco Systems
   510 McCarthy Blvd.
   Milpitas, CA  95035


   Stefano Previdi
   Cisco Systems
   Via Del Serafico 200
   Rome  0144


   Mach (Guoyi) Chen
   Huawei Technologies Co., Ltd
   KuiKe Building, No. 9 Xinxi Rd. Hai-Dian District
   Beijing  100085
   P.R. China


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