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Versions: (draft-ginsberg-isis-genapp) 00 01 02 03 04 RFC 6823

Network Working Group                                        L. Ginsberg
Internet-Draft                                                S. Previdi
Intended status: Standards Track                                M. Shand
Expires: December 22, 2008                                 Cisco Systems
                                                           June 20, 2008


                Advertising Generic Information in IS-IS
                     draft-ietf-isis-genapp-01.txt

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
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   This Internet-Draft will expire on December 22, 2008.

Abstract

   This draft describes the manner in which generic application
   information (i.e. information not directly related to the operation
   of the IS-IS protocol) SHOULD be advertised in IS-IS LSPs and defines
   guidelines which SHOULD be used when flooding such information.










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Table of Contents

   1.  Conventions used in this Document  . . . . . . . . . . . . . .  3
   2.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Encoding Format for GENINFO  . . . . . . . . . . . . . . . . .  3
     3.1.  GENINFO TLV  . . . . . . . . . . . . . . . . . . . . . . .  4
     3.2.  Use of subTLVs in GENINFO TLV  . . . . . . . . . . . . . .  6
     3.3.  Standardization Requirements . . . . . . . . . . . . . . .  6
   4.  GENINFO Flooding Procedures  . . . . . . . . . . . . . . . . .  6
     4.1.  Leaking Procedures . . . . . . . . . . . . . . . . . . . .  7
     4.2.  Minimizing Update Confusion  . . . . . . . . . . . . . . .  8
     4.3.  Interpreting Attribute Information . . . . . . . . . . . .  8
   5.  Use of a Separate Protocol Instance  . . . . . . . . . . . . .  8
   6.  Applicability of GENINFO TLV . . . . . . . . . . . . . . . . .  9
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 10
     10.2. Informative References . . . . . . . . . . . . . . . . . . 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
   Intellectual Property and Copyright Statements . . . . . . . . . . 12





























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1.  Conventions used in this Document

   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 [RFC2119].


2.  Overview

   [ISO10589] defines the format of TLVs which may be sent in IS-IS
   PDUs.  The first octet of a TLV encodes the "type" or "codepoint"
   which provides a scope for the information and information format
   which follows.  The protocol is therefore limited to 256 different
   codepoints which may be assigned.  This number has proved generous as
   regards the information required for correct operation of the IS-IS
   protocol.  However, the increasing use of IS-IS LSPs for
   advertisement of generic information (GENINFO) not directly related
   to the operation of the IS-IS protocol places additional demands on
   the TLV encoding space which has the potential to consume a
   significant number of TLV codepoints.  This document therefore
   defines an encoding format for GENINFO which minimizes the
   consumption of TLV codepoints and also maximizes the flexibility of
   the formats which can be used to represent GENINFO.

   This document also discusses optimal behavior associated with the
   advertisement and flooding of LSPs containing GENINFO in order to
   avoid the advertisement of stale information and minimize the
   presence of duplicate or conflicting information when advertisements
   are updated.

   The manner in which the information contained in GENINFO TLVs is
   exchanged between an instance of the IS-IS protocol and the
   application which generates/consumes the GENINFO is outside the scope
   of this specification.

   In order to minimize the impact advertisement of GENINFO may have on
   the operation of routing, such advertisements SHOULD occur in the
   context of a non-zero instance of the IS-IS protocol as defined in
   [I-D.previdi-isis-mi].


3.  Encoding Format for GENINFO

   The encoding format defined below has the following goals regarding
   the advertisement of GENINFO in IS-IS LSPs:






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   o  Minimize the number of codepoints required

   o  Minimize the depth of subTLV levels required

   In order to support these goals, a new IANA registry is required.
   This registry is required to manage the assignment of IS-IS GENINFO
   Application Identifiers.  These numbers are unsigned 16 bit numbers
   ranging in value from 1 to 65535.  The registry is also required to
   manage the assignment of application specific subTLV codepoints.
   These numbers are unsigned 8 bit numbers ranging in value from 0 to
   255.  The assignment of the subTLV codepoints is scoped by the
   Application Identifier.

3.1.  GENINFO TLV

   The GENINFO TLV supports the advertisement of application specific
   information which is not directly related to the operation of the
   IS-IS protocol.

   Type   251
   Length # of octets in the value field (3 to 255)
   Value

                                        No. of octets
              +-----------------------+
              | Flags                 |     1
              +-----------------------+
              | Application ID        |     2
              +-----------------------+
              | Application           |
              | IP Address Info       |     0 to 20
              +-----------------------+
              | Additional Application|     0 to (252 -
              |  Specific Information |     len of IP Address info)
              +-----------------------+


            Flags

                  0 1 2 3 4 5 6 7
                 +-+-+-+-+-+-+-+-+
                 |  Rsvd |V|I|D|S|
                 +-+-+-+-+-+-+-+-+


                 The following bit flags are defined.

                 S bit (0x01): If the S bit is set(1), the GENINFO TLV



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                 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 GENINFO TLV is leaked from
                 level-2 to level-1, the D bit MUST be set. Otherwise
                 this bit MUST be clear. GENINFO TLVs with the D bit set
                 MUST NOT be leaked from level-1 to level-2. This is to
                 prevent TLV looping.

                 I bit (0x04): When the I bit is set the 4 octet IPv4
                 address associated with the application immediately
                 follows the Application ID.

                 V bit (0x08): When the V bit is set, the 16 octet IPv6
                 address associated with the application immediately
                 follows either the Application ID (if I bit is clear)
                 or the IPv4 address (if I bit is set).

            Application ID

                 An identifier assigned to this application via the
                 GENINFO-REG.

            Application IPv4 Address Info

                 The IPv4 address associated with the application. This
                 is not necessarily an address of a router running the
                 IS-IS protocol.

            Application IPv6 Address Info

                 The IPv6 address associated with the application. This
                 is not necessarily an address of a router running the
                 IS-IS protocol.

            Additional Application Specific Information

                 Each application may define additional information to
                 be encoded in a GENINFO TLV following the fixed
                 information. Definition of such information is beyond
                 the scope of this document.


   The Application ID in combination with the Application IPv4/IPv6
   Address Information uniquely identifies the GENINFO Application
   Context (GENINFO-CTX).



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3.2.  Use of subTLVs in GENINFO TLV

   [RFC3784] introduced the definition and use of subTLVs.  One of the
   advantages of using subTLVs rather than fixed encoding of information
   inside a TLV is to allow for the addition of new information in a
   backwards compatible manner i.e. just as with TLVs, implementations
   are required to ignore subTLVs which they do not understand.

   GENINFO TLVs MAY include subTLVs in the application specific
   information as deemed necessary and appropriate for each application.
   The scope of the codepoints used in such subTLVs is defined by the
   GENINFO TLV codepoint AND the Application ID i.e. the subTLV
   codepoints are private to the application.  Such subTLVs are referred
   to as APPSUBTLVs and MUST be assigned via the GENINFO-REG IANA
   registry.

   Additional levels of APPSUBTLVs may be required when there is
   variable information which is scoped by a specific APPSUBTLV.  These
   "nested" subTLVs MUST be encoded in the same manner as subTLVs i.e.
   with a one-octet Type field, a one-octet Length field, and zero or
   more octets of Value.  These types MUST also be assigned via the
   GENINFO-REG IANA registry.

   The use of additional levels of subTLVs is discouraged due to the
   inherent inefficiency in encoding introduced because the parent
   subTLV must encode the nested subTLV length.  While this inefficiency
   is small (one additional octet), it may be sufficient to extend the
   total information about a single application object beyond the
   carrying capacity of a single GENINFO TLV.  Given that each
   Application ID can utilize the full range of subTLV codepoints (0 to
   255) without conflict with any other application, the need to be
   frugal in the use of APPSUBTLV codepoints is greatly reduced.

3.3.  Standardization Requirements

   GENINFO is intended to advertise information on behalf of
   applications whose operations have been defined in public documents.
   Therefore the uses of GENINFO MUST be standardized.

   GENINFO is NOT intended to be used for proprietary or experimental
   purposes.


4.  GENINFO Flooding Procedures

   This section describes procedures which apply to the propagation of
   LSPs which contain GENINFO TLVs.  These procedures have been
   previously discussed in [RFC4971].  This section is intended to serve



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   as a reference specification for future documents which define the
   use of GENINFO TLV(s) for a specific application - eliminating the
   need to repeat the definition of these procedures in the application
   specific documents.

   Each GENINFO TLV contains information regarding exactly one
   application instance as identified by the GENINFO-CTX.  When it is
   necessary to advertise sets of information with the same GENINFO-CTX
   which have different flooding scopes, a router MUST originate a
   minimum of one GENINFO TLV for each required flooding scope.  GENINFO
   TLVs which contain information having area/level scope will have the
   S bit clear.  These TLVs MUST NOT be leaked into another level.
   GENINFO TLVs which contain information which has domain scope will
   have the S bit set.  These TLVs MUST be leaked into other IS-IS
   levels.  When a TLV is leaked from level-2 to level-1, the D bit MUST
   be set in the level-1 LSP advertisement.

4.1.  Leaking Procedures

   When leaking GENINFO 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.  A router performing
   downward leaking MUST check for such duplication by comparing the
   contents of the TLVs.  The set of LSPs generated by a router for a
   given level MUST NOT contain two or more copies of the same GENTLV.

   In order to prevent the use of stale GENINFO information, a system
   MUST NOT use a GENINFO 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) associated with the LSP in which the GENINFO TLV appears.  Note
   that leaking a GENINFO TLV is one of the uses which is prohibited
   under these conditions.  The following example illustrates what might
   occur in the absence of this restriction.

   Example: If Level-1 router A generates a GENINFO TLV and floods it to
   two L1/L2 routers S and T, they will flood it into the Level-2 sub-
   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
   GENINFO 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 GENINFO TLV 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



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   stale information from A.

4.2.  Minimizing Update Confusion

   If an update to a TLV is advertised in an LSP with a different number
   than the LSP 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 which had the
   old advertisement and the LSP which has the new advertisement arrive
   at other systems.

   Whenever possible, an implementation SHOULD advertise the update to a
   GENINFO TLV in the LSP with the same number as the advertisement
   which it replaces.  Where this is not possible, the two affected LSPs
   SHOULD be flooded as an atomic action.

   Systems which receive an update to an existing GENINFO 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 LSPs associated with the same
   update prior to beginning processing.

4.3.  Interpreting Attribute Information

   Where a receiving system has two copies of a GENINFO TLV with the
   same GENINFO-CTX, attribute information in the two TLVs which does
   not conflict MUST be considered additive.  When information in the
   two GENINFO TLVs conflicts i.e there are different settings for a
   given attribute, the procedure used to choose which copy shall be
   used is undefined.


5.  Use of a Separate Protocol Instance

   The use of the IS-IS flooding mechanism as a means of reliably and
   efficiently propagating information is understandably attractive.
   However, it is prudent to remember that the primary purpose of that
   mechanism is to flood information necessary for the correct operation
   of the IS-IS protocol.  Flooding of information not directly related
   to the use of the IS-IS protocol in support of routing degrades the
   operation of the protocol.  Degradation occurs because the frequency
   of LSP updates is increased and because the processing of non-routing
   information in each router consumes resources whose primary
   responsibility is to efficiently respond to reachability changes in
   the network.

   Advertisement of GENINFO therefore SHOULD occur in the context of a



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   non-zero instance of the IS-IS protocol as defined in
   [I-D.previdi-isis-mi].  The use of a separate instance of the
   protocol allows both the flooding and the processing of the non-
   routing information to be decoupled from the information necessary to
   support correct routing of data in the network.  The flooding and
   processing of non-routing information can then be prioritized
   appropriately.

   Use of a separate protocol instance to advertise GENINFO does not
   eliminate the need to use prudence in the frequency with which such
   information is updated.  One of the most egregious oversights is a
   failure to appropriately dampen changes in the information to be
   advertised, which can lead to flooding storms.  Documents which
   specify the use of the mechanisms defined here MUST define the
   expected rate of change of the information to be advertised.


6.  Applicability of GENINFO TLV

   The GENINFO TLV supports the advertisement of application specific
   information in IS-IS LSPs which is not directly related to the
   operation of the IS-IS protocol.  Information which is not directly
   used by the IS-IS Decision process falls into this category.  The
   Decision Process is defined by [ISO10589] and extended by [RFC1195]
   and [RFC3906].

   The IS-IS WG of the IETF acts as the authority to determine whether
   information proposed to be advertised in IS-IS LSPs falls under this
   definition.

   The applicability statement above is expected to cover some
   information currently being advertised by IS-IS in previously defined
   TLVs.  It is expected and seen as desirable that an effort be made to
   migrate the advertisement of such information to utilize the
   procedures defined in this document.


7.  Security Considerations

   This document raises no new security issues for IS-IS.


8.  IANA Considerations

   This document defines a new ISIS TLV that needs to be reflected in
   the ISIS TLV code-point registry:





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   Type        Description                            IIH   LSP   SNP
   ----        -----------------------------------    ---   ---   ---
   251         Generic Information                     n     y     n

   This document also defines a new registry which needs to be created.

   The new registry is required to manage two types of assigned numbers:

   1)Application Identifiers which may be used in the Generic
   Information TLV.  These identifiers are unsigned 16 bit numbers
   ranging in value from 1 to 65535.

   2)Application specific subTLV codepoints which may be used in a
   GENINFO TLV when a specific Application Identifier is used.  These
   numbers are unsigned 8 bit numbers ranging in value from 0 to 255.


9.  Acknowledgements

   The authors would like to thank JP Vasseur and David Ward for
   providing the need to produce this document and Tony Li for making
   sure it was done with appropriate wisdom and prudence.


10.  References

10.1.  Normative References

   [ISO10589]
              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, December 1990.

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

   [RFC4971]  Vasseur, JP., Shen, N., and R. Aggarwal, "Intermediate
              System to Intermediate System (IS-IS) Extensions for
              Advertising Router Information", RFC 4971, July 2007.






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10.2.  Informative References

   [I-D.previdi-isis-mi]
              Previdi, S., "IS-IS Multi-instance",
              draft-previdi-isis-mi-00 (work in progress), May 2007.

   [RFC3784]  Smit, H. and T. Li, "Intermediate System to Intermediate
              System (IS-IS) Extensions for Traffic Engineering (TE)",
              RFC 3784, June 2004.

   [RFC3906]  Shen, N. and H. Smit, "Calculating Interior Gateway
              Protocol (IGP) Routes Over Traffic Engineering Tunnels",
              RFC 3906, October 2004.


Authors' Addresses

   Les Ginsberg
   Cisco Systems
   510 McCarthy Blvd.
   Milpitas, Ca.  95035
   USA

   Email: ginsberg@cisco.com


   Stefano Previdi
   Cisco Systems
   Via Del Serafico 200
   00142 - Roma,
   Italy

   Email: sprevidi@cisco.com


   Mike Shand
   Cisco Systems
   250, Longwater Avenue.
   Reading, Berks  RG2 6GB
   UK

   Email: mshand@cisco.com









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Full Copyright Statement

   Copyright (C) The IETF Trust (2008).

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   ietf-ipr@ietf.org.











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