[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits] [IPR]

Versions: (draft-vasseur-ccamp-loose-path-reopt) 00 01 02 RFC 4736

   CCAMP Working Group                            Jean-Philippe Vasseur
   IETF Internet Draft                                         (Editor)
   Proposed status: Informational                         Cisco Systems
                                                         Yuichi Ikejiri
                                                     NTT Communications
                                                            Corporation
                                                          Raymond Zhang
                                            Infonet Service Corporation

   Expires: November 2005                                      May 2005


       Reoptimization of Multiprotocol Label Switching (MPLS) Traffic
            Engineering (TE) loosely routed Label Switch Path (LSP)

                draft-ietf-ccamp-loose-path-reopt-01.txt


Status of this Memo

  By submitting this Internet-Draft, each author represents that any
  applicable patent or other IPR claims of which he or she is aware
  have been or will be disclosed, and any of which he or she becomes
  aware will be disclosed, in accordance with Section 6 of BCP 79.

  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-Drafts.

  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
  http://www.ietf.org/ietf/1id-abstracts.txt.

  The list of Internet-Draft Shadow Directories can be accessed at
  http://www.ietf.org/shadow.html.

Copyright Notice

   Copyright (C) The Internet Society (2005). All Rights Reserved.









draft-ietf-ccamp-loose-path-reopt-01.txt                  January 2005

Abstract

   This document defines a mechanism for the reoptimization of loosely
   routed MPLS and GMPLS (Generalized Multiprotocol Label Switching)
   Traffic Engineering LSPs. A loosely routed LSP is defined as one
   that does not contain a full explicit route identifying each LSR
   along the path of the LSP at the time it is signaled by the ingress
   LSR. Such an LSP is signaled with no ERO, with an ERO that contains
   at least one loose hop, or with an ERO that contains an abstract
   node that is not a simple abstract node (that is, an abstract node
   that identifies more than one LSR). This document proposes a
   mechanism that allows a TE LSP head-end LSR to trigger a new path re-
   evaluation on every hop having a next hop defined as a loose or
   abstract hop and a mid-point LSR to signal to the head-end LSR that a
   better path exists (compared to the current path in use) or that the
   TE LSP must be reoptimized because of some maintenance required on
   the TE LSP path.

   The proposed mechanism applies to the cases of intra and inter-domain
   (IGP area or Autonomous System) packet and non-packet TE LSPs
   following a loosely routed path.

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 RFC-2119.

Table of contents

   1. Notice.........................................................3
   2. Introduction...................................................3
   3. Establishment of a loosely routed TE LSP.......................4
   4. Reoptimization of a loosely routed TE LSP path.................5
   5. Signalling extensions..........................................6
      5.1 Path re-evaluation request.................................6
      5.2 New error value sub-codes..................................6
   6. Mode of operation..............................................7
      6.1 Head-end reoptimization control............................7
      6.2 Reoptimization triggers....................................7
      6.3 Head-end request versus mid-point explicit notification
      modes..........................................................7
   5.3.1 Head-end request mode.......................................7
   5.3.2 Mid-point explicit notification mode........................9
   5.3.3 ERO caching.................................................9
   7. Interoperability..............................................10
   8. Security considerations.......................................10
   9. IANA considerations...........................................10
   10. Acknowledgments..............................................10
   11. Intellectual property considerations.........................11


Vasseur, Ikejiri and Zhang                                    [Page 2]

draft-ietf-ccamp-loose-path-reopt-01.txt                  January 2005

   12. References...................................................11
   11.1 Normative references........................................11
   11.2 Informative references......................................11
   13. Authors' Addresses...........................................12
   14. Full Copyright Statement.....................................12

1. Notice

   The procedures described in this document are entirely optional
   within an MPLS or GMPLS network. Implementations that do not support
   the procedures described in this document will interoperate
   seamlessly with those that do. Further, an implementation that does
   not support the procedures described in this document will not be
   impacted or implicated by a neighboring implementation that does
   implement the procedures.

   An ingress implementation that chooses not to support the procedures
   described in this document may still achieve re-optimization by
   periodically issuing a speculative make-before-break replacement of
   an LSP without trying to discovery whether a more optimal path is
   available in a downstream domain. Such a procedure would not be in
   conflict with any mechanisms not already documented in [RFC3209] and
   [RFC3473].

2. Introduction

   The Traffic Engineering Work Group has specified a set of
   requirements for inter-area [INTER-AREA-TE-REQ] and inter-AS [INTER-
   AS-TE-REQ] MPLS Traffic Engineering. Both requirements documents
   specify the need for some mechanism providing an option for the head-
   end to control the reoptimization process, should a more optimal path
   exist in a downstream domain (IGP area or Autonomous System).

   This document defines a solution to meet this requirement and
   proposes a set of mechanisms that allow:

      - The TE LSP head-end LSR to trigger a new path re-evaluation on
     every hop having a next hop defined as a loose hop or abstract
     node,

      - A mid-point LSR to signal to the head-end LSR that either a
     better path exists to reach a loose/abstract hop (compared to the
     current path in use) or that the TE LSP must be reoptimized because
     of some maintenance required on the TE LSP path. A better path is
     defined as a lower cost path, where the cost is determined by the
     metric used to compute the path.






Vasseur, Ikejiri and Zhang                                    [Page 3]

draft-ietf-ccamp-loose-path-reopt-01.txt                  January 2005

3. Establishment of a loosely routed TE LSP

   In the context of this document, a loosely routed LSP is defined as
   one that does not contain a full explicit route identifying each LSR
   along the path of the LSP at the time it is signaled by the ingress
   LSR. Such an LSP is signaled with no ERO, with an ERO that contains
   at least one loose hop, or with an ERO that contains an abstract
   node that is not a simple abstract node (that is, an abstract node
   that identifies more than one LSR). As defined in [RFC3209], loose
   hops are listed in the Explicit Route Object (ERO) of the RSVP Path
   message with the L flag of the IPv4 or the IPv6 prefix sub-object
   set.

   Each LSR along the path whose next hop is specified as a loose hop or
   a non-specific abstract node triggers a path computation (also
   referred to as an ERO expansion), before forwarding the RSVP Path
   message downstream. The computed path may either be partial (up to
   the next loose hop) or complete (set of strict hops up to the TE LSP
   destination).

   Note that the examples in the rest of this document are provided in
   the context of MPLS inter-area TE but the proposed mechanism equally
   applies to loosely routed paths within a single routing domain and
   across multiple Autonomous Systems.

   The examples below are provided with OSPF as the IGP but the
   described set of mechanisms similarly apply to IS-IS.

   An example of an explicit loosely routed TE LSP signaling.

   <---area 1--><-area 0--><-area 2->

    R1---R2----R3---R6    R8---R10
     |          |    |   / | \  |
     |          |    |  /  |  \ |
     |          |    | /   |   \|
    R4---------R5---R7----R9---R11

   Assumptions
   - R3, R5, R8 and R9 are ABRs
   - The path of an inter-area TE LSP T1 from R1 (head-end LSR) to R11
   (tail-end LSR) is defined on R1 as the following loosely routed path:
   R1-R3(loose)-R8(loose)-R11(loose). R3, R8 and R11 are defined as
   loose hops.

   Step 1: R1 determines that the next hop (R3) is a loose hop (not
   directly connected to R1) and then performs an ERO expansion
   operation to reach the next loose hops R3. The new ERO becomes:
   R2(S)-R3(S)-R8(L)-R11(L) where:
      S: Strict hop (L=0)


Vasseur, Ikejiri and Zhang                                    [Page 4]

draft-ietf-ccamp-loose-path-reopt-01.txt                  January 2005

      L: Loose hop (L=1)

   The R1-R2-R3 path obeys T1's set of constraints.

   Step 2: the RSVP Path message is then forwarded by R1 following the
   ERO path and reaches R3 with the following content: R8(L)-R11(L)

   Step 3: R3 determines that the next hop (R8) is a loose hop (not
   directly connected to R3) and then performs an ERO expansion
   operation to reach the next loose hops R8. The new ERO becomes:
   R6(S)-R7(S)-R8(S)-R11(L).

   Note: in this example, the assumption is made that the path is
   computed on a per loose hop basis, also referred to a partial route
   computation. Note that some path computation techniques may result in
   complete paths (set of strict hops up to the final destination).

   Step 4: the same procedure applies at R8 to reach T1's destination
   (R11).

4. Reoptimization of a loosely routed TE LSP path

   Once a loosely routed explicit TE LSP is set up, it is maintained
   through normal RSVP procedures. During TE LSP life time, a more
   optimal path might appear between an LSR and its next loose hop (for
   the sake of illustration, suppose in the example above that a link
   between R6 and R8 is added or restored that provides a preferable
   path between R3 and R8 (R3-R6-R8) than the existing R3-R6-R7-R8
   path). Since a preferable (e.g. shorter) path might not be visible
   from the head-end LSR by means of the IGP if it does not belong to
   the head-end IGP area, the head-end cannot make use of this shorter
   path (and reroute the LSP using a make before break) when
   appropriate. Hence, some mechanism is required to detect the
   existence of such a preferable path and to notify the head-end
   accordingly.

   This document defines a mechanism that allows:

        - A head-end LSR to trigger on every LSR whose next hop is a
        loose hop or an abstract node the re-evaluation of the current
        path in order to detect a potential more optimal path,

        - A mid-point LSR whose next hop is a loose-hop or an abstract
        node to signal (using a new Error value sub-code carried in a
        RSVP PathErr message) to the head-end that a more preferable
        path exists (a path with a lower cost, where the cost definition
        is determined by some metric).

   Then once the existence of such a preferable path is notified to the
   head-end LSR, the head-end LSR can decide (depending on the TE LSP


Vasseur, Ikejiri and Zhang                                    [Page 5]

draft-ietf-ccamp-loose-path-reopt-01.txt                  January 2005

   characteristics) whether to perform a TE LSP graceful reoptimization
   such as the "Make Before Break" procedure defined in [RFC3209].

   There is another scenario whereby notifying the head-end of the
   existence of a better path is desirable: if the current path is about
   the fail due to some (link or node) required maintenance.

   This allows the head-end to reoptimize a TE LSP making use of the non
   disruptive make before break procedure if and only if a preferable
   path exists and if such a reoptimization is desired.

5. Signalling extensions

   A new flag in the SESSION ATTRIBUTE object and new Error value sub-
   codes in the ERROR SPEC object are proposed in this document (to be
   assigned by IANA).

5.1 Path re-evaluation request

   The following new flag of the SESSION_ATTRIBUTE object (C-Type 1 and
   7) is defined (suggested value to be confirmed by IANA):

           Path re-evaluation request:  0x20

   This flag indicates that a path re-evaluation (of the current path in
   use) is requested. Note that this does not trigger any LSP Reroute
   but instead just signals the request to evaluate whether a preferable
   path exists.

   Note: in case of link bundling for instance, although the resulting
   ERO might be identical, this might give the opportunity for a mid-
   point LSR to locally select another link within a bundle, although
   strictly speaking, the ERO has not changed.

5.2 New error value sub-codes

   As defined in [RFC3209], the ERROR-CODE 25 in ERROR SPEC object
   corresponds to a Notify Error.

   This document adds three new error value sub-codes (suggested values
   to be confirmed by IANA):

      6  Preferable path exists
      7  Local link maintenance required
      8  Local node maintenance required

   The details about the local maintenance required modes are detailed
   in section 5.3.2




Vasseur, Ikejiri and Zhang                                    [Page 6]

draft-ietf-ccamp-loose-path-reopt-01.txt                  January 2005

6. Mode of operation

6.1 Head-end reoptimization control

   The notification process of a preferable path (shorter path or new
   path due to some maintenance required on the current path) is by
   nature de-correlated from the reoptimization operation. In other
   words, the location where a potentially preferable path is discovered
   does not have to be where the TE LSP is actually reoptimized. This
   document applies to the context of a head-end reoptimization.

6.2 Reoptimization triggers

   There are three possible reoptimization triggers:

   - Timer-based: a reoptimization is triggered (process evaluating
   whether a more optimal path can be found) when a configurable timer
   expires,
   - Event-driven: a reoptimization is triggered when a particular
   network event occurs (such as a "Link-UP" event),
   - Operator-driven: a reoptimization is manually triggered by the
   Operator.

   It is RECOMMENDED for an implementation supporting the extensions
   proposed in this document to support the aforementioned modes as path
   re-evaluation triggers.

6.3 Head-end request versus mid-point explicit notification modes

   This document defines two modes:

        1) "Head-end requesting mode": the request for a new path
        evaluation of a loosely routed TE LSP is requested by the head-
        end LSR.

        2) "Mid-point explicit notification": a mid-point LSR having
        determined that a preferable path (than the current path is use)
        exists or having the need to perform a link/node local
        maintenance explicitly notifies the head-end LSR which will in
        turn decide whether to perform a reoptimization.

6.3.1 Head-end request mode

   In this mode, when a timer-based reoptimization is triggered on the
   head-end LSR or the operator manually requests a reoptimization, the
   head-end LSR immediately sends an RSVP Path message with the "Path
   re-evaluation request" bit of the SESSION-ATTRIBUTE object set. This
   bit is then cleared in subsequent RSVP path messages sent downstream.
   In order to handle the case of a lost Path message, the solution



Vasseur, Ikejiri and Zhang                                    [Page 7]

draft-ietf-ccamp-loose-path-reopt-01.txt                  January 2005

   consists of relying on the reliable messaging mechanism described in
   [REFRESH-REDUCTION].

   Upon receiving a Path message with the "Path re-evaluation request"
   bit set, every LSR for which the next abstract node contained in the
   ERO is defined as a loose hop/abstract node, performs the following
   set of actions:

   A path re-evaluation is triggered and the newly computed path is
   compared to the existing path:

        - If a preferable path can be found, the LSR performing the path
        re-evaluation MUST immediately send an RSVP PathErr to the head-
        end LSR (Error code 25 (Notify), Error sub-code=6 (better path
        exists)). At this point, the LSR MAY decide to not propagate
        such bit in subsequent RSVP Path messages sent downstream for
        the re-evaluated TE LSP: this mode is the RECOMMENDED mode for
        the reasons described below.

        The sending of an RSVP PathErr Notify message "Preferable path
        exists" to the head-end LSR will notify the head-end LSR of the
        existence of a preferable path (e.g in a downstream area/AS or
        in another location within a single domain). Hence, triggering
        additional path re-evaluations on downstream nodes is
        unnecessary. The only motivation to forward subsequent RSVP Path
        messages with the "Path re-evaluation request" bit of the
        SESSION-ATTRIBUTE object set would be to trigger path re-
        evaluation on downstream nodes that could in turn cache some
        potentially better paths downstream with the objective to reduce
        the signaling setup delay, should a reoptimization be performed
        by the head-end LSR.

        - If no preferable path can be found, the recommended mode is
        for an LSR to relay the request (by setting the "Path re-
        evaluation" bit of the SESSION-ATTRIBUTE object in RSVP path
        message sent downstream).

   Note that, by preferable path, we mean a path having a lower cost.

   If the RSVP Path message with the "Path re-evaluation request" bit
   set is lost, then the next request will be sent when the next
   reoptimization trigger will occur on the head-end LSR. The solution
   to handle RSVP reliable messaging has been defined in [REFRESH-
   REDUCTION].

   The network administrator may decide to establish some local policy
   specifying to ignore such request or to consider those requests not
   more frequently than a certain rate.




Vasseur, Ikejiri and Zhang                                    [Page 8]

draft-ietf-ccamp-loose-path-reopt-01.txt                  January 2005

   The proposed mechanism does not make any assumption of the path
   computation method performed by the ERO expansion process.

6.3.2 Mid-point explicit notification mode

   In this mode, a mid-point LSR whose next hop is a loose hop or an
   abstract node can locally trigger a path re-evaluation when a
   configurable timer expires, some specific events occur (e.g. link-up
   event for example) or the user explicitly requests it. If a
   preferable path is found compared to the existing one, the LSR sends
   an RSVP PathErr to the head-end LSR (Error code 25 (Notify), Error
   sub-code=6 ("preferable path exists").

   There are other circumstances whereby any mid-point LSR MAY send an
   RSVP PathErr message with the objective for the TE LSP to be rerouted
   by its head-end LSR: when a link or a node will go down for local
   maintenance reasons. In this case, the LSR where a local maintenance
   must be performed is responsible for sending an RSVP PathErr message
   with Error code 25 and Error sub-code=7 or 8 depending on the
   affected network element (link or node). Then the first upstream node
   having performed the ERO expansion MUST perform the following set of
   actions:

        - The link (sub-code=7) or the node (sub-code=8) MUST be
        locally registered for further reference (the TE database must
        be updated)

        - The RSVP PathErr message MUST be immediately forwarded
        upstream to the head-end LSR. Note that in the case of TE LSP
        spanning multiple administrative domains, it may be desirable
        for the boundary LSR to modify the RSVP PathErr message and
        insert its own address for confidentiality reason.

   Upon receiving an RSVP PathErr message with Error code 25 and Error
   sub-code 7 or 8, the Head-end LSR MUST perform a TE LSP
   reoptimization.

   Note that those modes are not exclusive: both the timer and event-
   driven reoptimization triggers can be implemented on the head-end
   and/or any mid-point LSR with potentially different timer values for
   the timer driven reoptimization case.

   A head-end LSR MAY decide upon receiving an explicit mid-point
   notification to delay its next path re-evaluation request.

6.3.3 ERO caching

   Once a mid-point LSR has determined that a preferable path exists
   (after a reoptimization request has been received by the head-end LSR
   or the reoptimization timer on the mid-point has fired), the more


Vasseur, Ikejiri and Zhang                                    [Page 9]

draft-ietf-ccamp-loose-path-reopt-01.txt                  January 2005

   optimal path MAY be cached on the mid-point LSR for a limited amount
   of time to avoid having to recompute a path once the head-LSR
   performs a make before break. This mode is optional. A default value
   of 5 seconds is suggested.

7. Interoperability

   An LSR not supporting the "Path re-evaluation request" bit of the
   SESSION-ATTRIBUTE object SHALL forward it unmodified.

   A head-end LSR not supporting an RSVP PathErr with Error code 25
   message and Error sub-code = 6, 7 or 8 MUST just silently ignore such
   RSVP PathErr message.


8. Security considerations

   This document defines a mechanism for a mid-point LSR to notify the
   head-end LSR of this existence of a preferable path or the need to
   reroute the TE LSP for maintenance purposes. Hence, in case of a TE
   LSP spanning multiple administrative domains, it may be desirable for
   a boundary LSR to modify the RSVP PathErr message (Code 25, Error
   sub-code=6,7 or 8) so as to preserve confidentiality across domains.
   Furthermore, a head-end LSR may decide to ignore explicit
   notification coming from a mid-point residing in another domain.
   Similarly, an LSR may decide to ignore (or accept but up to a pre-
   defined rate) path re-evaluation requests originated by a head-end
   LSR of another domain.

9. IANA considerations

   IANA will assign a new flag named "Path re-evaluation request" in the
   SESSION-ATTRIBUTE object (C-Type 1 and 7) specified in [RFC3209].
   Suggested value is (to be confirmed by IANA) 0x20.

   IANA will also assign three new error sub-code values for the RSVP
   PERR Notify message (Error code=25). Suggested values are (to be
   confirmed by IANA):

      6  Preferable path exists
      7  Local link maintenance required
      8  Local node maintenance required

10. Acknowledgments

   The authors would like to thank Carol Iturralde, Miya Kohno, Francois
   Le Faucheur, Philip Matthews, Jim Gibson, Jean-Louis Le Roux, Kenji
   Kumaki, Anca Zafir, Dimitri Papadimitriou for their useful comments.
   A special thank to Adrian Farrel for his very valuable inputs.



Vasseur, Ikejiri and Zhang                                   [Page 10]

draft-ietf-ccamp-loose-path-reopt-01.txt                  January 2005


11. 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
   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
   http://www.ietf.org/ipr.

   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-ipr@ietf.org.

12. References

12.1 Normative references

   [RFC] Bradner, S., "Key words for use in RFCs to Indicate Requirement
   Levels," RFC 2119.

   [RFC3209] Awduche et al, "RSVP-TE: Extensions to RSVP for LSP
   Tunnels",  RFC3209, December 2001.

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

   [REFRESH-REDUCTION] Berger et al, "RSVP Refresh Overhead Reduction
   Extensions", RFC2961, April 2001.

12.2 Informative references

   [TE-REQ] Awduche et al, "Requirements for Traffic Engineering over
   MPLS", RFC2702, September 1999.

   [INTER-AREA-TE-REQ], Le Roux, Vasseur, Boyle et al. "Requirements
   for Inter-area MPLS Traffic Engineering", draft-ietf-tewg-interarea-
   mpls-te-req-03, November 2004.


Vasseur, Ikejiri and Zhang                                   [Page 11]

draft-ietf-ccamp-loose-path-reopt-01.txt                  January 2005


   [INTER-AS-TE-REQ] Zhang et al, "MPLS Inter-AS Traffic Engineering
   requirements", draft-ietf-tewg-interas-mpls-te-req-09.txt, September
   2004, Work in progress.

   [INTER-DOMAIN-FW] Farrel A., Vasseur JP. and Ayyangar A., "A
   Framework for Inter-Domain MPLS Traffic Engineering", draft-ietf-
   ccamp-inter-domain-framework-02.txt, May 2005. Work in progress.

   [INTER-DOMAIN-SIG] Ayyangar A. and Vasseur JP., "Inter domain GMPLS
   Traffic Engineering - RSVP-TE extensions", draft-ietf-ccamp-inter-
   domain-rsvp-te-00.txt", February 2005. Work in progress.

   [INTER-DOMAIN-PATH-COMP] Vasseur JP., Ayyangar A., "A Per-domain
   path computation method for computing Inter-domain Traffic
   Engineering (TE) Label Switched Path (LSP)", draft-ietf-ccamp-inter-
   domain-pd-path-comp-00.txt, February 2005. Work in progress.

13. Authors' Addresses

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

      Yuichi Ikejiri
      NTT Communications Corporation
      1-1-6, Uchisaiwai-cho, Chiyoda-ku
      Tokyo 100-8019
      JAPAN
      Email: y.ikejiri@ntt.com

      Raymond Zhang
      Infonet Services Corporation
      2160 E. Grand Ave.
      El Segundo, CA 90025
      USA
      Email: raymond_zhang@infonet.com


14. 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
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS


Vasseur, Ikejiri and Zhang                                   [Page 12]

draft-ietf-ccamp-loose-path-reopt-01.txt                  January 2005

   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR
   IMPLIED,INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.















































Vasseur, Ikejiri and Zhang                                   [Page 13]


Html markup produced by rfcmarkup 1.108, available from http://tools.ietf.org/tools/rfcmarkup/