GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc6823

Internet Engineering Task Force (IETF) L. Ginsberg Request for Comments: 6823 S. Previdi Category: Standards Track M. Shand ISSN: 2070-1721 Cisco Systems

                                                         December 2010
              Advertising Generic Information in IS-IS

Abstract

 This document describes the manner in which generic application
 information (i.e., information not directly related to the operation
 of the Intermediate System to Intermediate System (IS-IS) protocol)
 should be advertised in IS-IS Link State Protocol Data Units (LSPs)
 and defines guidelines that should be used when flooding such
 information.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc6823.

Copyright Notice

 Copyright (c) 2010 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
 (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.  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.

Ginsberg, et al. Standards Track [Page 1] RFC 6823 Advertising Generic Information in IS-IS December 2010

Table of Contents

 1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  2
 2.  Conventions Used in This Document  . . . . . . . . . . . . . .  3
 3.  Encoding Format for GENINFO  . . . . . . . . . . . . . . . . .  3
   3.1.  GENINFO TLV  . . . . . . . . . . . . . . . . . . . . . . .  3
   3.2.  Use of Sub-TLVs in GENINFO TLV . . . . . . . . . . . . . .  5
 4.  GENINFO Flooding Procedures  . . . . . . . . . . . . . . . . .  5
   4.1.  Leaking Procedures . . . . . . . . . . . . . . . . . . . .  6
   4.2.  Minimizing Update Confusion  . . . . . . . . . . . . . . .  7
   4.3.  Interpreting Attribute Information . . . . . . . . . . . .  7
 5.  Use of a Separate Protocol Instance  . . . . . . . . . . . . .  7
 6.  Applicability of GENINFO TLV . . . . . . . . . . . . . . . . .  8
 7.  Standardization Requirements . . . . . . . . . . . . . . . . .  8
 8.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
 9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  9
 11. Normative References . . . . . . . . . . . . . . . . . . . . . 10

1. Overview

 [ISO10589] defines the format of Type-Length-Values (TLVs) that may
 be sent in IS-IS Protocol Data Units (PDUs).  The first octet of a
 TLV encodes the "type" or "codepoint" that provides a scope for the
 information and information format that follows.  The protocol is
 therefore limited to 256 different codepoints that 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 Link State Protocol Data Units (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 that have the potential to consume a significant
 number of TLV codepoints.  This document therefore defines an
 encoding format for GENINFO that minimizes the consumption of TLV
 codepoints and also maximizes the flexibility of the formats that 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 that generates or consumes the GENINFO is outside the
 scope of this specification.

Ginsberg, et al. Standards Track [Page 2] RFC 6823 Advertising Generic Information in IS-IS December 2010

 In order to minimize the impact that advertisement of GENINFO may
 have on the operation of routing, such advertisements MUST occur in
 the context of a non-zero instance of the IS-IS protocol as defined
 in [RFC6822] except where the rules for the use of the zero instance
 set out later in this document are followed.

2. 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].

3. Encoding Format for GENINFO

 The encoding format defined below has the following goals regarding
 the advertisement of GENINFO in IS-IS LSPs:
 o  Minimize the number of IS-IS top level and sub-TLV codepoints
    required
 o  Minimize the depth of sub-TLV levels required
 In order to support these goals, a new IANA registry has been
 created.  This registry manages the assignment of IS-IS GENINFO
 Application Identifiers.  These numbers are unsigned 16-bit numbers
 ranging in value from 1 to 65535.  Application-specific sub-TLV
 codepoints are unsigned 8-bit numbers ranging in value from 0 to 255.
 The assignment of the sub-TLV codepoints is scoped by the Application
 Identifier.  Management of the application specific sub-TLV
 codepoints is outside the scope of this document.

3.1. GENINFO TLV

 The GENINFO TLV supports the advertisement of application-specific
 information that is not directly related to the operation of the
 IS-IS protocol.
   Type:   251
   Length: Number of octets in the value field (3 to 255)

Ginsberg, et al. Standards Track [Page 3] RFC 6823 Advertising Generic Information in IS-IS December 2010

   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 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 IANA registry
    defined later in this document.

Ginsberg, et al. Standards Track [Page 4] RFC 6823 Advertising Generic Information in IS-IS December 2010

 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.

3.2. Use of Sub-TLVs in GENINFO TLV

 [RFC5305] introduced the definition and use of sub-TLVs.  One of the
 advantages of using sub-TLVs 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 sub-TLVs that they do
 not understand.
 GENINFO TLVs MAY include sub-TLVs in the application specific
 information as deemed necessary and appropriate for each application.
 The scope of the codepoints used in such sub-TLVs is defined by the
 combination of the GENINFO TLV codepoint and the Application ID,
 i.e., the sub-TLV codepoints are private to the application.  Such
 sub-TLVs are referred to as APPsub-TLVs.
 Additional levels of APPsub-TLVs may be required when there is
 variable information that is scoped by a specific APPsub-TLV.  These
 "nested" sub-TLVs MUST be encoded in the same manner as sub-TLVs,
 i.e., with a one-octet Type field, a one-octet Length field, and zero
 or more octets of Value.

4. GENINFO Flooding Procedures

 This section describes procedures that apply to the propagation of
 LSPs that contain GENINFO TLVs.  These procedures have been
 previously discussed in [RFC4971].  This section is intended to serve
 as a reference specification for future documents that 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 Application ID in the
 GENINFO TLV.  When it is necessary to advertise sets of information

Ginsberg, et al. Standards Track [Page 5] RFC 6823 Advertising Generic Information in IS-IS December 2010

 with the same Application ID that have different flooding scopes, a
 router MUST originate a minimum of one GENINFO TLV for each required
 flooding scope.  GENINFO TLVs that contain information having area/
 level scope will have the S bit clear.  These TLVs MUST NOT be leaked
 into another level.  GENINFO TLVs that contain information that 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 GENINFO
 TLV.
 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 that 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 that 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
 stale information from A.

Ginsberg, et al. Standards Track [Page 6] RFC 6823 Advertising Generic Information in IS-IS December 2010

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 that had the
 old advertisement and the LSP that 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 that
 it replaces.  Where this is not possible, the two affected LSPs
 SHOULD be flooded as an atomic action.
 Systems that receive an update to an existing GENINFO TLV can
 minimize the potential disruption associated with the update by
 employing a hold-down 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 Application ID, attribute information in the two TLVs that 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 MUST occur in the context of a
 non-zero instance of the IS-IS protocol as defined in [RFC6822]
 except when the use in the zero instance is defined in a Standards
 Track RFC.

Ginsberg, et al. Standards Track [Page 7] RFC 6823 Advertising Generic Information in IS-IS December 2010

 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; this can lead to flooding storms.  Documents that specify
 the use of the mechanisms defined here MUST define the expected rate
 of change of the information to be advertised.
 If desirable, independent control of the flooding scope for
 information related to two different applications can be achieved by
 utilizing separate non-zero protocol instances for each application
 [RFC6822].

6. Applicability of GENINFO TLV

 The GENINFO TLV supports the advertisement of application-specific
 information in IS-IS LSPs that is not directly related to the
 operation of the IS-IS protocol.  Information advertised in the
 GENINFO TLV MUST NOT alter basic IS-IS protocol operation including
 (but not limited to) the establishment of adjacencies, the update
 process, and the decision process.

7. Standardization Requirements

 GENINFO is intended to advertise information on behalf of
 applications whose operations have been defined in a public
 specification as discussed in [RFC5226].
 The public specification MUST include:
 o  a description of the sub-TLV allocation policy
 o  discussion of security issues
 o  discussion of the rate of change of the information being
    advertised
 o  justification for the use of GENINFO

Ginsberg, et al. Standards Track [Page 8] RFC 6823 Advertising Generic Information in IS-IS December 2010

8. Security Considerations

 The introduction and use of the new TLV codepoint for GENINFO in and
 of itself raises no new security issues for IS-IS.
 It is possible that information advertised in a GENINFO TLV by a
 given application MAY introduce new security issues.  The public
 specification that defines the use of GENINFO by that application
 MUST include a discussion of the security issues.  Where appropriate,
 it is recommended that either [RFC5304] or [RFC5310] be used.

9. IANA Considerations

 Per this document, IANA has registered a new IS-IS TLV in the "IS-IS
 TLV Codepoints" registry:
 Type     Description                           IIH   LSP   SNP  Purge
 ----     ----------------------------------    ---   ---   ---  -----
 251      Generic Information                    n     y     n     n
 IANA has also created a new registry.  The new registry manages the
 assignment of Application Identifiers that may be used in the Generic
 Information TLV.  These identifiers are unsigned 16-bit numbers
 ranging in value from 1 to 65535.  The value 0 is reserved.  The
 registration procedure is "Expert Review" as defined in [RFC5226].
 The expert MUST verify that the public specification that defines the
 use of GENINFO for the application adequately discusses all points
 mentioned in Section 7 of this document.
 The following information MUST be specified in the registry:
 o  ID Value (1-65535)
 o  Description
 o  Allowed in Instance zero (Y/N)
 o  Reference Specification

10. 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.

Ginsberg, et al. Standards Track [Page 9] RFC 6823 Advertising Generic Information in IS-IS December 2010

11. 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.
 [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.
 [RFC5226]   Narten, T. and H. Alvestrand, "Guidelines for Writing an
             IANA Considerations Section in RFCs", BCP 26, RFC 5226,
             May 2008.
 [RFC5304]   Li, T. and R. Atkinson, "IS-IS Cryptographic
             Authentication", RFC 5304, October 2008.
 [RFC5305]   Li, T. and H. Smit, "IS-IS Extensions for Traffic
             Engineering", RFC 5305, October 2008.
 [RFC5310]   Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
             and M. Fanto, "IS-IS Generic Cryptographic
             Authentication", RFC 5310, February 2009.
 [RFC6822]   Previdi, S., Ginsberg, L., Shand, M., Roy, A., and D.
             Ward, "IS-IS Multi-Instance", RFC 6822, December 2012.

Ginsberg, et al. Standards Track [Page 10] RFC 6823 Advertising Generic Information in IS-IS December 2010

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: imc.shand@gmail.com

Ginsberg, et al. Standards Track [Page 11]

/data/webs/external/dokuwiki/data/pages/rfc/rfc6823.txt · Last modified: 2012/12/22 01:21 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki