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Versions: 00 01 02 03 draft-ietf-mpls-p2mp-loose-path-reopt

MPLS Working Group                                       Tarek Saad, Ed.
Internet-Draft                                        Rakesh Gandhi, Ed.
Intended status: Standards Track                               Zafar Ali
Expires: September 11, 2014                          Cisco Systems, Inc.
                                                       Robert H. Venator
                                      Defense Information Systems Agency
                                                             Yuji Kamite
                                          NTT Communications Corporation
                                                          March 10, 2014


       Reoptimization of Point-to-Multipoint Traffic Engineering
                          Loosely Routed LSPs
               draft-tsaad-mpls-p2mp-loose-path-reopt-01


Abstract

   This document defines Resource Reservation Protocol - Traffic
   Engineering (RSVP-TE) signaling extensions for reoptimizing loosely
   routed Point-to-Multipoint (P2MP) Traffic Engineered (TE) Label
   Switched Paths (LSPs) in an Multi-Protocol Label Switching (MPLS) and
   Generalized MPLS (GMPLS) networks.

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."













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Copyright Notice

   Copyright (c) 2014 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
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   described in the Simplified BSD License.












Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
     2.1.  Conventions used in this document  . . . . . . . . . . . .  4
   3.  Signaling Procedure For Loosely Routed P2MP-TE LSP
       Reoptimization . . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  RSVP Signaling Extensions  . . . . . . . . . . . . . . . . . .  6
     4.1.  P2MP-TE Tree Re-evaluation Request Flag  . . . . . . . . .  6
     4.2.  Preferable P2MP-TE Tree Exists Path Error sub-code . . . .  6
   5.  Compatibility  . . . . . . . . . . . . . . . . . . . . . . . .  6
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . .  6
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  7
     7.1.  P2MP-TE Tree Re-evaluation Request Flag  . . . . . . . . .  7
     7.2.  Preferable P2MP-TE Tree Exists Path Error sub-code . . . .  7
   8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . .  7
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     9.1.  Normative References . . . . . . . . . . . . . . . . . . .  8
     9.2.  Informative References . . . . . . . . . . . . . . . . . .  8
   Author's Addresses . . . . . . . . . . . . . . . . . . . . . . . .  9





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1.  Introduction

   This document defines Resource Reservation Protocol (RSVP) signaling
   extensions for reoptimizing loosely routed Point-to-Multipoint (P2MP)
   Multi-Protocol Label Switching (MPLS) and Generalized MPLS (GMPLS)
   Traffic Engineered (TE) Label Switched Paths (LSPs) [RFC4875].

   A P2MP-TE LSP is comprised of one or more source-to-leaf (S2L)
   sub-LSPs.  A loosely routed P2MP-TE S2L sub-LSP is defined as one
   whose path does not contain the full explicit route identifying each
   node along the path to the egress node at the time of its signaling
   by the ingress node.  Such an S2L sub-LSP is signaled with no
   Explicit Route Object (ERO) [RFC3209], or 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 node).  This is often the case with inter-
   domain P2MP-TE LSPs where Path Computation Element (PCE) is not used
   [RFC5440].

   As per [RFC4875], an ingress node may reoptimize the entire P2MP-TE
   LSP by resignaling all its S2L sub-LSP(s) or may reoptimize
   individual S2L sub-LSP(s) i.e. individual destination(s).

   [RFC4736] defines RSVP signaling extensions for reoptimizing loosely
   routed P2P TE LSP(s).  Specifically, an ingress node sends a "Path
   Re-evaluation Request" to a border node by setting a flag (0x20) in
   SESSION_ATTRIBUTES object in the Path message.  A border node sends a
   PathErr code 25 (notify error defined in [RFC3209]) with sub-code 6
   to indicate "Preferable Path Exists" to the ingress node which may be
   solicited or unsolicited.  The ingress node upon receiving this
   PathErr either solicited or unsolicited initiates reoptimization of
   the LSP.

   [RFC4736] does not define signaling extensions specific for
   reoptimizing entire P2MP-TE LSP tree.  Mechanisms defined in
   [RFC4736] can be used for signaling the reoptimization of individual
   S2L sub- LSP(s).  However, to use [RFC4736] mechanisms for
   reoptimizing an entire P2MP-TE LSP tree, an ingress node needs to
   send the query on all (typically 100s of) S2L sub-LSPs and a border
   node needs to notify PathErrs for all S2L sub-LSPs.  Such requirement
   can lead to the following issues.

   - A border node has to accumulate the received queries on all S2L
   sub-LSPs (using a wait timer) and interpret them as a reoptimization
   request for the P2MP-TE LSP tree.  A border node may prematurely
   notify "Preferable Path Exists" for a sub-set of S2L sub-LSPs.

   - When the ingress node gradually receives unsolicited PathErr



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   notifications for individual S2L sub-LSPs, it may prematurely start
   reoptimizing a sub-set of S2L sub-LSPs.  However, as mentioned in
   [RFC4875] Section 14.2, such reoptimization procedure may result in
   data duplication that can be avoided if the entire P2MP-TE LSP tree
   is reoptimized, especially if the ingress node eventually receives
   PathErr notifications for all S2L sub-LSPs of the P2MP-TE LSP tree.

   - The ingress node may have to heuristically determine when to
   perform entire P2MP-TE LSP tree reoptimization versus per S2L sub-LSP
   reoptimization, for example, to delay reoptimization long enough time
   to accumulate all PathErr(s) to be received.  Such requirements may
   produce undesired results due to timing related issues which can be
   easily avoided by the RSVP signaling messages defined in this
   document.

   This document defines RSVP signaling extensions to query and notify a
   preferable path for reoptimizing loosely routed P2MP-TE LSP tree.

2.  Terminology

   ABR: Area Border Router.

   ERO: Explicit Route Object.

   TE LSP: Traffic Engineering Label Switched Path.

   TE LSP ingress: head/source of the TE LSP.

   TE LSP egress: tail/destination of the TE LSP.

   S2L: Source-to-leaf.

   Interior Gateway Protocol Area (IGP Area): OSPF Area or IS-IS level.

   Inter-area TE LSP: A TE LSP whose path transits across at least two
   different IGP areas.

   Inter-AS MPLS TE LSP: A TE LSP whose path transits across at least
   two different Autonomous Systems (ASes) or sub-ASes (BGP
   confederations).

2.1.  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].  The reader
   is assumed to be familiar with the terminology in [RFC4875] and
   [RFC4736].



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3.  Signaling Procedure For Loosely Routed P2MP-TE LSP Reoptimization

   As per [RFC4875], an ingress node may prefer to reoptimize the entire
   P2MP-TE LSP by resignaling all its S2L sub-LSP(s) (Section 14.1,
   "Make-before- Break") or reoptimize individual S2L sub-LSP(s) i.e.
   individual destination(s) (Section 14.2 "Sub-Group-Based Re-
   Optimization").

   An ingress node uses procedures defined in [RFC4736] to individually
   reoptimize the S2L sub-LSP(s) i.e. destination(s) of a P2MP-TE LSP.

   To reoptimize an entire P2MP-TE LSP tree, in order to query border
   nodes to check if a preferable P2MP-TE LSP tree exists, an ingress
   node sends a Path message with "P2MP-TE Tree Re-evaluation Request"
   defined in this document.  An ingress node may select one or more S2L
   sub-LSP of the P2MP-TE LSP tree transiting through the border node to
   send the query to that border node.

   A border node receiving the "P2MP-TE Tree Re-evaluation Request"
   checks for a preferable P2MP-TE LSP tree by re-evaluating loosely
   expanded paths for all S2L sub-LSP(s) of the P2MP-TE LSP.  If a
   preferable P2MP-TE LSP tree is found, the border node immediately
   sends an RSVP PathErr to the ingress node with Error code 25 (Notify
   defined in [RFC3209] and Error sub-code defined in this document
   "Preferable P2MP-TE Tree Exists".  At this point, the border node
   does not propagate this bit in subsequent RSVP Path messages sent
   downstream for the re-evaluated P2MP-TE LSP.  The sending of an RSVP
   PathErr Notify message "Preferable P2MP-TE Tree Exists" to the
   ingress node will notify the ingress node of the existence of a
   preferable P2MP-TE LSP tree.

   If no preferable path for P2MP-TE LSP tree can be found, the
   recommended mode is for the border node to relay the request
   downstream by setting the "P2MP-TE Tree Re-evaluation Request" bit in
   the LSP_ATTRIBUTES TLV of RSVP Path message.

   A border node may send "Preferable P2MP-TE Tree Exists" with PathErr
   code 25 to the ingress node to notify an existence of a preferred
   path for the P2MP-TE LSP tree with an unsolicited PathErr message.
   The border node may select one or more S2L sub-LSP(s) of the P2MP-TE
   LSP tree to send this PathErr message to the ingress node.










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4.  RSVP Signaling Extensions

4.1.  P2MP-TE Tree Re-evaluation Request Flag

   In order to query border nodes to check if a preferable P2MP-TE LSP
   tree exists, a new flag is defined in Attributes Flags TLV of the
   LSP_ATTRIBUTES object [RFC5420] as follows:

      Bit Number (to be assigned by IANA): P2MP-TE Tree Re-evaluation
            Request flag

   The "P2MP-TE Tree Re-evaluation Request" flag is meaningful in a Path
   message of a P2MP-TE S2L sub-LSP and is inserted by the ingress node.


4.2.  Preferable P2MP-TE Tree Exists Path Error sub-code

   In order to indicate to an ingress node that a preferable P2MP-TE LSP
   tree is available, following new sub-code for PathErr code 25 (Notify
   Error) [RFC3209] is defined:

      Sub-code (to be assigned by IANA):  Preferable P2MP-TE Tree Exists
            sub-code


   When a preferable path for P2MP-TE LSP tree is found, the border node
   sends a solicited or unsolicited "Preferable P2MP-TE Tree Exists"
   PathErr notification to the ingress node of the P2MP-TE LSP.

5.  Compatibility

   The LSP_ATTRIBUTES TLV has been defined in [RFC5420] with class
   numbers in the form 11bbbbbb, which ensures compatibility with
   non-supporting nodes.  Per [RFC2205], nodes not supporting this
   extension will ignore the new flag defined in this document but
   forward it without modification.

6.  Security Considerations

   This document does not introduce any additional security issues above
   those identified in [RFC3209] and [RFC4875].










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7.  IANA Considerations

   IANA maintains a name space for RSVP-TE TE parameters "Resource
   Reservation Protocol-Traffic Engineering (RSVP-TE) Parameters".  From
   the registries in this name space "Attribute Flags" allocation of new
   flag is requested (Section 4.1).

   IANA also maintains a name space for RSVP protocol parameters
   "Resource Reservation Protocol (RSVP) Parameters".  From the sub-
   registry "Sub-Codes - 25 Notify Error" in registry "Error Codes and
   Globally-Defined Error Value Sub-Codes" allocation of a new error
   code is requested (Section 4.2).

7.1.  P2MP-TE Tree Re-evaluation Request Flag

   The following new flag is defined for the Attributes Flags TLV in the
   LSP_ATTRIBUTES object [RFC5420].  The numeric values are to be
   assigned by IANA.

   o  P2MP-TE Tree Re-evaluation Request Flag:

        - Bit Number: To be assigned by IANA.

        - Attribute flag carried in Path message: Yes

        - Attribute flag carried in Resv message: No


7.2.  Preferable P2MP-TE Tree Exists Path Error sub-code

   As defined in [RFC3209], the Error Code 25 in the ERROR SPEC object
   corresponds to a Notify Error PathErr.  This document adds a new sub-
   code as follows for this PathErr:

   o  Preferable P2MP-TE Tree Exists sub-code:

        - Sub-code for Notify PathErr code 25. To be assigned by IANA.


8.  Acknowledgments

   TBA.









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9.  References

9.1.  Normative References

   [RFC2205]  Braden, R., Ed., Zhang, L., Berson, S., Herzog, S., and S.
              Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
              Functional Specification", RFC 2205, September 1997.

   [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.

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

   [RFC5420]  Farrel, A., Papadimitriou, D., Vasseur, JP., and A.
              Ayyangarps, "Encoding of Attributes for MPLS LSP
              Establishment Using Resource Reservation Protocol Traffic
              Engineering (RSVP-TE)", RFC 5420, February 2009.

9.2.  Informative References

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

   [RFC4736]  Vasseur, JP., Ikejiri, Y. and Zhang, R, "Reoptimization of
              Multiprotocol Label Switching (MPLS) Traffic Engineering
              (TE) Loosely Routed Label Switched Path (LSP)", RFC 4736,
              November 2006.

   [RFC5440]  Vasseur, JP., Ed., and JL. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol (PCEP)", RFC 5440,
              March 2009.
















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Author's Addresses


   Tarek Saad (editor)
   Cisco Systems

   Email: tsaad@cisco.com


   Rakesh Gandhi (editor)
   Cisco Systems

   Email: rgandhi@cisco.com


   Zafar Ali
   Cisco Systems

   Email: zali@cisco.com


   Robert H. Venator
   Defense Information Systems Agency

   Email: robert.h.venator.civ@mail.mil


   Yuji Kamite
   NTT Communications Corporation

   Email: y.kamite@ntt.com




















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