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Versions: (draft-berger-ccamp-assoc-info) 00 01 02 03 RFC 6689

Internet Draft                                         Lou Berger (LabN)
Category: Informational
Expiration Date: April 25, 2012

                                                        October 25, 2011

                  Usage of The RSVP Association Object

                   draft-ietf-ccamp-assoc-info-03.txt

Abstract

   The RSVP ASSOCIATION object was defined in the context of GMPLS
   (Generalized Multi-Protocol Label Switching) controlled label
   switched paths (LSPs).  In this context, the object is used to
   associate recovery LSPs with the LSP they are protecting.  This
   document reviews how association is to be provided in the context
   of GMPLS recovery.  No new procedures or mechanisms are
   defined by this document and it is strictly informative in nature.

Status of this Memo

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Copyright and License Notice

   Copyright (c) 2011 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



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   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  ...........................................   3
    2      Background  .............................................   3
    2.1    LSP Association  ........................................   3
    2.2    End-to-End Recovery LSP Association  ....................   5
    2.3    Segment Recovery LSP Association  .......................   8
    2.4    Resource Sharing LSP Association  .......................   8
    3      Association of GMPLS Recovery LSPs  .....................   9
    4      Security Considerations  ................................  10
    5      IANA Considerations  ....................................  10
    6      Acknowledgments  ........................................  10
    7      References  .............................................  10
    7.1    Normative References  ...................................  10
    7.2    Informative References  .................................  11
    8      Author's Addresses  .....................................  11


























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1. Introduction

   End-to-end and segment recovery are defined for GMPLS (Generalized
   Multi-Protocol Label Switching) controlled label switched paths
   (LSPs) in [RFC4872] and [RFC4873] respectively.  Both definitions use
   the ASSOCIATION object to associate recovery LSPs with the LSP they
   are protecting.  This document provides additional narrative on how
   such associations are to be identified.  This document does not
   define any new procedures or mechanisms and is strictly informative
   in nature.

   It may not be immediately obvious to the informed reader why this
   document is necessary, however questions were repeatedly raised in
   the Common Control and Measurement Plane (CCAMP) working group on the
   proper interpretation of the ASSOCIATION object in the context of
   end-to-end and segment recovery, and the working group agreed that
   this document should be produced in order to close the matter.  This
   document formalizes the explanation provided in an e-mail to the
   working group authored by Adrian Farrel, see [AF-EMAIL].  This
   document in no way modifies the normative definitions of end-to-end
   and segment recovery, see [RFC4872] or [RFC4873].


2. Background

   This section reviews the definition of LSP association in the
   contexts of end-to-end and segment recovery as defined in [RFC4872]
   and [RFC4873].  This section merely reiterates what has been defined,
   if differences exist between this text and [RFC4872] or [RFC4873],
   the earlier RFCs provide the authoritative text.


2.1. LSP Association

   [RFC4872] introduces the concept and mechanisms to support the
   association of one LSP to another LSP across different RSVP-TE
   sessions.  Such association is enabled via the introduction of the
   ASSOCIATION object.  The ASSOCIATION object is defined in Section 16
   of [RFC4872].  It is explicitly defined as having both general
   application and specific use within the context of recovery.  End-to-
   end recovery usage is defined in [RFC4872] and is covered in Section
   2.2.  Segment recovery usage is defined in [RFC4873] and is covered
   in Section 2.3.  Resource sharing LSP association is also defined in
   [RFC4873], while strictly speaking such association is beyond the
   scope of this document, for completeness it is covered in Section
   2.4.  The remainder of this section covers generic usage of the
   ASSOCIATION object.

   In general, LSP association using the ASSOCIATION object can take
   place based on the values carried in the ASSOCIATION object.  This
   means that association between LSPs can take place independent from



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   and across different sessions.  This is a significant enhancement
   from the association of LSPs that is possible in base MPLS [RFC3209]
   and GMPLS [RFC3473].

   When using ASSOCIATION object, LSP association is always initiated by
   an upstream node that inserts appropriate ASSOCIATION objects in the
   Path message of LSPs that are to be associated.  Downstream nodes
   then correlate LSPs based on received ASSOCIATION objects.  Multiple
   types of LSP association is supported by the ASSOCIATION object, and
   downstream correlation is made based on the type.

   [RFC4872] defines C-Types 1 and 2 of the ASSOCIATION object.  Both
   objects have essentially the same semantics, only differing in the
   type of address carried (IPv4 and IPv6). The defined objects carry
   multiple fields. The fields, taken together, enable the
   identification of which LSPs are association with one another.  The
   [RFC4872] defined fields are:

     o Association Type:
       This field identifies the usage, or application, of the
       association object.  The currently defined values are Recovery
       [RFC4872] and Resource Sharing [RFC4873].  This field also scopes
       the interpretation of the object. In other words, the type field
       is included when matching LSPs (i.e., the type fields must
       match), and the way associations are identified may be type
       dependent.

     o Association Source:
       This field is used to provide global scope (within the address
       space) to the identified association.  There are no specific
       rules in the general case for which address should be used by a
       node creating an ASSOCIATION object beyond that the address is
       "associated to the node that originated the association", see
       [RFC4872].

     o Association ID:
       This field provides an "identifier" that further scopes an
       association.  Again, this field is combined with the other
       ASSOCIATION object fields to support identification of associated
       LSPs.  The generic definition does not provide any specific rules
       on how matching is to be done, so such rules are governed by the
       Association Type. Note that the definition permits the
       association of an arbitrary number of LSPs.

   As defined, the ASSOCIATION object may only be carried in a Path
   message, so LSP association takes place based on Path state.  The
   definition permits one or more objects to be present.  The support
   for multiple objects enables an LSP to be associated with other LSPs
   in more than one way at a time.  For example, an LSP may carry one
   ASSOCIATION object to associate the LSP with another LSP for end-to-
   end recovery, and at the same time carry a second ASSOCIATION object



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   to associate the LSP with another LSP for segment recovery, and at
   the same time carry a third ASSOCIATION object to associate the LSP
   with yet another LSP for resource sharing.


2.2. End-to-End Recovery LSP Association

   The association of LSPs in support of end-to-end LSP recovery is
   defined in Section 16.2 of [RFC4872].  There are also several
   additional related conformance statements (i.e., use of [RFC2119]
   defined key words) in Sections 7.3, 8.3, 9.3, 11.1.  When analyzing
   the definition, as with any Standards Track RFC, it is critical to
   note and differentiate which statements are made using [RFC2119]
   defined key words, which relate to conformance, and which statements
   are made without such key words, which are only informative in
   nature.

   As defined in Section 16.2, end-to-end recovery related LSP
   association may take place in two distinct forms:

      a. Between multiple (one or more) working LSPs and a single shared
         (associated) recovery LSP.  This form essentially matches the
         shared 1:N (N >= 1) recovery type described in the other
         sections of [RFC4872].

      b. Between a single working LSP and multiple (one or more)
         recovery LSPs.  This form essentially matches all other
         recovery types described in [RFC4872].

   Both forms share the same Association Type (Recovery) and the same
   Association Source (the working LSP's tunnel sender address).  They
   also share the same definition of the Association ID, which is
   (quoting [RFC4872]):

      "The Association ID MUST be set to the LSP ID of the LSP being
      protected by this LSP or the LSP protecting this LSP.  If unknown,
      this value is set to its own signaled LSP ID value (default).
      Also, the value of the Association ID MAY change during the
      lifetime of the LSP."

   The interpretation of the above is fairly straightforward.  The
   Association ID carries one of 3 values:
     - The LSP ID of the LSP being protected.
     - The LSP ID of the LSP protecting an LSP.
     - In the case where the matching LSP is not yet known (i.e.,
       initiated), the LSP ID value of the LSP itself.

   The text also explicitly allows for changing the Association ID
   during the lifetime of an LSP.  But this is only an option, and is
   neither required (i.e., "MUST") nor recommended (i.e., "SHOULD").  It
   should be noted that the document does not describe when such a



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   change should be initiated, or the procedures for such a change.
   Clearly care needs to be taken when changing the Association ID to
   ensure that the old association is not lost during the transition to
   a new association.

   The text does not preclude, and it is therefore assumed, that one or
   more ASSOCIATION objects may also be added to an LSP that was
   originated without any ASSOCIATION objects.  Again this is a case
   that is not explicitly discussed in [RFC4872].

   From the above, this means that the following combinations may occur:

      Case 1. When the ASSOCIATION object of the LSP being protected is
              initialized before the ASSOCIATION objects of any recovery
              LSPs are initialized, the Association ID in the LSP being
              protected and any recovery LSPs will carry the same value
              and this value will be the LSP ID value of the LSP being
              protected.

      Case 2. When the ASSOCIATION object of a recovery LSP is
              initialized before the ASSOCIATION object of any protected
              LSP is initialized, the Association ID in the recovery LSP
              and any LSPs being protected by that LSP will carry the
              same value and this value will be the LSP ID value of the
              recovery LSP.

      Case 3. When the ASSOCIATION objects of both the LSP being
              protected and the recovery LSP are concurrently
              initialized, the value of the Association ID carried in
              the LSP being protected is the LSP ID value of the
              recovery LSP, and the value of the Association ID carried
              in the recovery LSP is the LSP ID value of the LSP being
              protected.  As this case can only be applied to LSPs with
              matching tunnel sender addresses, the scope of this case
              is limited to end-to-end recovery.  Note that this is
              implicit in [RFC4872] as its scope is limited to end-to-
              end recovery.

   In practical terms, case 2 will only occur when using the shared 1:N
   (N >= 1) end-to-end recovery type and case 1 will occur with all
   other end-to-end recovery types.  Case 3 is allowed, and it is
   subject to interpretation how often it will occur.  Some believe that
   this case is the common case and, furthermore, that working and
   recovery LSPs will often first be initiated without any ASSOCIATION
   objects and then case 3 objects will be added once the LSPs are
   established.  Others believe that case 3 will rarely if ever occur.
   Such perspectives have little impact on interoperability as a
   [RFC4872] compliant implementation needs to properly handle (identify
   associations for) all three cases.

   It is important to note that Section 16.2 of [RFC4872] provides no



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   further requirements on how or when the Association ID value is to be
   selected. The other sections of the document do provide further
   narrative and 3 additional requirements.  In general, the narrative
   highlights case 3 identified above but does not preclude the other
   cases.  The 3 additional requirements are, by [RFC4872] Section
   number:

     o Section 7.3 -- "The Association ID MUST be set by default to the
       LSP ID of the protected LSP corresponding to N = 1."

       When considering this statement together with the 3 cases
       enumerated above, it can be seen that this statement clarifies
       which LSP ID value should be used when a single shared protection
       LSP is established simultaneously with (case 3), or after (case
       2), and more than one LSP to be protected.

     o Section 8.3 -- "Secondary protecting LSPs are signaled by setting
       in the new PROTECTION object the S bit and the P bit to 1, and in
       the ASSOCIATION object, the Association ID to the associated
       primary working LSP ID, which MUST be known before signaling of
       the secondary LSP."

       This requirement clarifies that when using the Rerouting without
       Extra-Traffic type of recovery it is required to follow either
       case 1 or 3, but not 2, as enumerated above.

     o Section 9.3 -- "Secondary protecting LSPs are signaled by setting
       in the new PROTECTION object the S bit and the P bit to 1, and in
       the ASSOCIATION object, the Association ID to the associated
       primary working LSP ID, which MUST be known before signaling of
       the secondary LSP."

       This requirement clarifies that when using the Shared-Mesh
       Restoration type of recovery it is required to follow either case
       1 or 3, but not 2, as enumerated above.

     o Section 11.1 -- "In both cases, the Association ID of the
       ASSOCIATION object MUST be set to the LSP ID value of the
       signaled LSP."

       This requirement clarifies that when using the LSP Rerouting type
       of recovery it is required to follow either case 1 or 3, but not
       2, as enumerated above.











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2.3. Segment Recovery LSP Association

   GMPLS segment recovery is defined in [RFC4873]. Segment recovery
   reuses the LSP association mechanisms, including the Association Type
   field value, defined in [RFC4872].  The primary text to this effect
   in [RFC4873] is:

      3.2.1.  Recovery Type Processing

      Recovery type processing procedures are the same as those
      defined in [RFC4872], but processing and identification occur
      with respect to segment recovery LSPs.  Note that this means
      that multiple ASSOCIATION objects of type recovery may be
      present on an LSP.

   This statement means that case 2 as enumerated above is to be
   followed and furthermore that Association Source is set to the tunnel
   sender address of the segment recovery LSPs.  The explicit exclusion
   of case 3 is not listed as its non-applicability was considered
   obvious to the informed reader.  (Perhaps having this exclusion
   explicitly identified would have obviated the need for this
   document.)


2.4. Resource Sharing LSP Association

   Section 3.2.2 of [RFC4873] defines an additional type of LSP
   association which is used for "Resource Sharing".  Resource sharing
   enables the sharing of resources across LSPs with different SESSION
   objects. Without this object only sharing across LSPs with a shared
   SESSION object was possible, see [RFC3209].

   Resource sharing is indicated using a new Association Type value.  As
   the Association Type field value is not the same as is used in
   Recovery LSP association, the semantics used for the association of
   LSPs using an ASSOCIATION object containing the new type differs from
   Recovery LSP association.

   Section 3.2.2 of [RFC4873] states the following rules for the
   construction of an ASSOCIATION object in support of resource sharing
   LSP association:

     o The Association Type value is set to "Resource Sharing".

     o Association Source is set to the originating node's router
       address.

     o The Association ID is set to a value that uniquely identifies the
       set of LSPs to be associated.

       The setting of the Association ID value to the working LSP's LSP



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       ID value is mentioned, but using the "MAY" key word.  Per
       [RFC2119], this translates to the use of LSP ID value as being
       completely optional and that the choice of Association ID is
       truly up to the originating node.

   Additionally, the identical ASSOCIATION object is used for all LSPs
   that should be associated using Resource Sharing.  This differs from
   recovery LSP association where it is possible for the LSPs to carry
   different Association ID fields and still be associated (see case 3
   in Section 2.2).


3. Association of GMPLS Recovery LSPs

   The previous section reviews the construction of an ASSOCIATION
   object, including the selection of the value used in the Association
   ID field, as defined in [RFC4872] and [RFC4873]. This section reviews
   how a downstream receiver identifies that one LSP is associated
   within another LSP based on ASSOCIATION objects.  Note that this
   section in no way modifies the normative definitions of end-to-end
   and segment recovery, see [RFC4872] or [RFC4873].

   As the ASSOCIATION object is only carried in Path messages, such
   identification only takes place based on Path state.  In order to
   support the identification of the recovery type association between
   LSPs, a downstream receiver needs to be able to handle all three
   cases identified in Section 2.2.  Cases 1 and 2 are simple as the
   associated LSPs will carry the identical ASSOCIATION object.  This is
   also always true for resource sharing type LSP association, see
   Section 2.4. Case 3 is more complicated as it is possible for the
   LSPs to carry different Association ID fields and still be
   associated. The receiver also needs to allow for changes in the set
   of ASSOCIATION objects included in an LSP.

   Based on the [RFC4872] and [RFC4873] definitions related to the
   ASSOCIATION object, the following behavior can be followed to ensure
   that a receiver always properly identifies the association between
   LSPs:

     o Covering cases 1 and 2 and resource sharing type LSP association:

       For ASSOCIATION objects with the Association Type field values of
       "Recovery" (1) and "Resource Sharing" (2), the association
       between LSPs is identified by comparing all fields of each of the
       ASSOCIATION objects carried in the Path messages associated with
       each LSP.  An association is deemed to exist when the same values
       are carried in all fields of an ASSOCIATION object carried in
       each LSP's Path message.  As more than one association may exist
       (e.g., in support of different association types or end-to-end
       and segment recovery), all carried ASSOCIATION objects need to be
       examined.



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     o Covering case 3:

       Any ASSOCIATION object with the Association Type field value of
       "Recovery" (1) that does not yield an association in the prior
       comparison needs to be checked to see if a case 3 association is
       indicated. As this case only applies to end-to-end recovery, the
       first step is to locate any other LSPs with the identical SESSION
       object fields and the identical tunnel sender address fields as
       the LSP carrying the ASSOCIATION object.  If such LSPs exist, a
       case 3 association is identified by comparing the value of the
       Association ID field with the LSP ID field of the other LSP.  If
       the values are identical, then an end-to-end recovery association
       exists.  As this behavior only applies to end-to-end recovery,
       this check need only be performed at the egress.

   No additional behavior is needed in order to support changes in the
   set of ASSOCIATION objects included in an LSP, as long as the change
   represents either a new association or a change in identifiers made
   as described in Section 2.2.


4. Security Considerations

   This document reviews procedures defined in [RFC4872] and [RFC4873]
   and does not define any new procedures.  As such, no new security
   considerations are introduced in this document.


5. IANA Considerations

   There are no new IANA considerations introduced by this document.


6. Acknowledgments

   This document formalizes the explanation provided in an e-mail to the
   working group authored by Adrian Farrel, see [AF-EMAIL]. This
   document was written in response to questions raised in the CCAMP
   working group by Nic Neate <nhn@dataconnection.com>.  Valuable
   comments and input was also received from Dimitri Papadimitriou,
   Francois Le Faucheur and Ashok Narayanan.


7. References

7.1. Normative References

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





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   [RFC4872]  Lang, J., Rekhter, Y., and Papadimitriou, D., "RSVP-TE
              Extensions in Support of End-to-End Generalized Multi-
              Protocol Label Switching (GMPLS) Recovery", RFC 4872,
              May 2007.

   [RFC4873]  Berger, L., Bryskin, I., Papadimitriou, D., Farrel, A.,
              "GMPLS Segment Recovery", RFC 4873, May 2007.

   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan,
              V., and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
              Tunnels", RFC 3209, December 2001.

   [RFC3473]  Berger, L., "Generalized Multi-Protocol Label Switching
              (GMPLS) Signaling Resource ReserVation Protocol-Traffic
              Engineering (RSVP-TE) Extensions", RFC 3473, January
              2003.


7.2. Informative References

   [AF-EMAIL] Farrel, A. "Re: Clearing up your misunderstanding of
       the Association ID", CCAMP working group mailing list,
       http://www.ietf.org/mail-archive/web/ccamp/current/msg00644.html,
       November 18, 2008.


8. Author's Addresses

   Lou Berger
   LabN Consulting, L.L.C.
   Phone: +1-301-468-9228
   Email: lberger@labn.net






















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