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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: January 22, 2015                            Cisco Systems, Inc.
                                                       Robert H. Venator
                                      Defense Information Systems Agency
                                                             Yuji Kamite
                                          NTT Communications Corporation
                                                           July 21, 2014


       Reoptimization of Point-to-Multipoint Traffic Engineering
                          Loosely Routed LSPs
               draft-tsaad-mpls-p2mp-loose-path-reopt-03


Abstract

   For a Traffic Engineered (TE) point-to-multipoint (P2MP) Label
   Switched Path (LSP), it is preferable in some cases to re-evaluate
   and re-optimize the entire P2MP-TE LSP by re-signaling all its S2L
   sub-LSP(s). Existing mechanisms allow the path re-evaluation and the
   signaling of a the notification of preferred path exists for a single
   S2L sub-LSP only.

   This document defines RSVP-TE signaling extensions to allow an
   ingress Label Switching Router (LSR) of a P2MP-TE LSP to trigger the
   re-evaluation of the entire LSP tree containing one or more S2L sub-
   LSPs whose paths are loose (or abstract) hop expanded, and for a mid-
   point LSR to signal to the ingress LSR that a better tree exists for
   the entire P2MP-TE LSP.

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
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."





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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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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.









Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
     2.1.  Abbreviations  . . . . . . . . . . . . . . . . . . . . . .  4
     2.2.  Nomenclatures  . . . . . . . . . . . . . . . . . . . . . .  5
     2.3.  Conventions used in this document  . . . . . . . . . . . .  5
   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  . . . . . . . . . . . . . . . . . . . . . . . .  7
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . .  7
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  7
     7.1.  P2MP-TE Tree Re-evaluation Request Flag  . . . . . . . . .  8
     7.2.  Preferable P2MP-TE Tree Exists Path Error sub-code . . . .  8
   8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . .  8
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     9.1.  Normative References . . . . . . . . . . . . . . . . . . .  9
     9.2.  Informative References . . . . . . . . . . . . . . . . . .  9
   Author's Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10






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1.  Introduction

   This document defines Resource Reservation Protocol - Traffic
   Engineering (RSVP-TE) [RFC2205] [RFC3209] signaling extensions for
   re-optimizing loosely routed Point-to-Multipoint (P2MP) Traffic
   Engineered (TE) Label Switched Paths (LSPs) [RFC4875] in an
   Multi-Protocol Label Switching (MPLS) and/or Generalized MPLS (GMPLS)
   networks.

   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 re-optimize the entire P2MP-TE
   LSP by re-signaling all its S2L sub-LSP(s) or may re-optimize
   individual S2L sub-LSP(s) i.e. individual destination(s).

   [RFC4736] defines RSVP signaling extensions for re-optimizing loosely
   routed P2P TE LSP(s) as follows.

   - A mid-point LSR that expands loose next-hop(s) MAY send a solicited
   or unsolicited PathErr with the Notify error code (25 as defined in
   [RFC3209]) with sub-code 6 to indicate "Preferable Path Exists" to
   the ingress node.

   - An ingress node MAY trigger a path re-evaluation request at all
   mid-point LSR(s) that expands loose next-hop(s) by setting the "Path
   Re-evaluation Request" flag (0x20) in SESSION_ATTRIBUTES object in
   the Path message.

   - The ingress node upon receiving this PathErr either solicited or
   unsolicited initiates re-optimization of the LSP.


   [RFC4736] does not define signaling extensions specific for re-
   optimizing entire P2MP-TE LSP tree.  Mechanisms defined in [RFC4736]
   can be used for signaling the re-optimization of individual S2L sub-
   LSP(s). However, to use [RFC4736] mechanisms for re-optimizing an
   entire P2MP-TE LSP tree, an ingress node needs to send the path re-
   evaluation requests on all (typically 100s of) S2L sub-LSPs and the



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   mid-point LSR to notify PathErrs for all S2L sub-LSPs.  Such a
   procedure may lead to the following issues:

   - A mid-point LSR that expands loose next-hop(s) may have to
   accumulate the received path re-evaluation request(s) for all S2L
   sub-LSPs (e.g, by using a wait timer) and interpret them as a re-
   optimization request for the whole P2MP-TE LSP tree.  Otherwise, A
   mid-point LSR may prematurely notify "Preferable Path Exists" for one
   or a sub-set of S2L sub-LSPs.

   - The ingress LSR that receives (un)solicited PathErr notification(s)
   for individual S2L sub-LSP(s), may prematurely start re-optimizing
   the sub-set of S2L sub-LSPs.  However, as mentioned in [RFC4875]
   Section 14.2, such re-optimization procedure may result in data
   duplication that can be avoided if the entire P2MP-TE LSP tree is re-
   optimized, 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 re-optimization versus per S2L sub-
   LSP re-optimization, for example, to delay re-optimization long
   enough to allow all PathErr(s) to be received.  Once all PathErr(s)
   are received, the ingress node has to accumulate them to see if re-
   optimization of the entire P2MP-TE is necessary.  Such procedures may
   produce undesired results due to timing related issues.  This may be
   easily avoided by the RSVP signaling messages defined in this
   document.

   This document defines RSVP-TE signaling extensions for the head-end
   LSR of a P2MP-TE LSP to trigger the re-evaluation of the P2MP tree on
   every hop that has a next hop defined as a loose or abstract hop for
   one or more S2L sub-LSP path, and a mid-point LSR to signal to the
   head-end LSR that a better tree exists (compared to the current path)
   or that the whole P2MP-TE LSP must be re-optimized (because of
   maintenance required on the TE LSP path).


2.  Terminology

2.1.  Abbreviations

   ABR: Area Border Router.

   AS: Autonomous System.

   ERO: Explicit Route Object.

   TE LSP: Traffic Engineering Label Switched Path.



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

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
















































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2.2.  Nomenclatures

   Domain: Routing or administrative domain such as an IGP area and an
   autonomous system.

   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).

   S2L sub-LSP: Source-to-leaf sub Label Switched Path.

2.3.  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].

3.  Signaling Procedure For Loosely Routed P2MP-TE LSP Re-Optimization

   It might be preferable, as per [RFC4875], to re-optimize the entire
   P2MP-TE LSP by re-signaling all of its S2L sub-LSP(s) (Section 14.1,
   "Make-before- Break") or re-optimize individual S2L sub-LSP(s) i.e.
   individual destination(s) (Section 14.2 "Sub-Group-Based Re-
   Optimization"). This can be achieved by using the procedures defined
   in [RFC4736] to individually re-optimize the S2L sub-LSP(s) of a
   P2MP-TE LSP.

   To evaluate an entire P2MP-TE LSP tree on mid-point LSRs that expand
   loose next-hop(s), an ingress node may send 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 to trigger the re-evaluation request(s).

   A mid-point LSR that expands loose next-hop(s) for one or more S2L
   sub-LSP path(s), and that receives a Path message with the "P2MP-TE
   Tree Re-evaluation Request" bit set, checks for a preferable P2MP-TE
   LSP tree by re-evaluating all S2L sub-LSP(s) expanded paths of the
   P2MP-TE LSP.  If a preferable P2MP-TE LSP tree is found, the mid-
   point LSR 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".  The mid-point LSR, in



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   turn, does not propagate the "P2MP-TE Tree Re-evaluation Request" 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. In
   addition, a mid-point LSR may send an unsolicited PathErr message
   with "Preferable P2MP-TE Tree Exists" PathErr code 25 to the ingress
   node to notify of a preferred the P2MP-TE LSP tree when it determines
   it exists. In this case, the mid-point LSR that expands loose next-
   hop(s) for one or more S2L sub-LSP path(s) may select one or more S2L
   sub-LSP(s) of the P2MP-TE LSP tree to send this PathErr message to
   the ingress node.

   If no preferable tree for P2MP-TE LSP can be found, the recommended
   mode is for the mid-point LSR that expands loose next-hop(s) for one
   or more S2L sub-LSP path(s) to propagate the request downstream by
   setting the "P2MP-TE Tree Re-evaluation Request" bit in the
   LSP_ATTRIBUTES object of RSVP Path message.

4.  RSVP Signaling Extensions

4.1.  P2MP-TE Tree Re-evaluation Request Flag

   In order to trigger a tree re-evaluation request, 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 exists, the 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 exists, the mid-point LSR
   sends a solicited or unsolicited "Preferable P2MP-TE Tree Exists"
   PathErr notification to the ingress node of the P2MP-TE LSP.





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5.  Compatibility

   The LSP_ATTRIBUTES object 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 defines a mechanism for a mid-point LSR to notify the
   ingress node of a P2MP-TE LSP of the existence of a preferable tree.
   As per [RFC4736], in the case of a P2MP-TE LSP S2L sub-LSP spanning
   multiple domains, it may be desirable for a a mid-point LSR to modify
   the RSVP PathErr message defined in this document to maintain
   confidentiality across different domains.  Furthermore, an ingress
   node may decide to ignore this PathErr message coming from a mid-
   point LSR residing in another domain.  Similarly, an mid-point LSR
   may decide to ignore the tree re-evaluation request originating from
   another ingress domain.

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).


















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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 value is to be assigned
   by IANA.

   o  P2MP-TE Tree Re-evaluation Request Flag:

   +--------+---------------+---------+---------+---------+------------+
   | Bit No | Attribute     | Carried | Carried | Carried | Reference  |
   |        | Flag Name     | in Path | in Resv | in RRO  |            |
   +--------+---------------+---------+---------+---------+------------+
   | TBA by | P2MP-TE Tree  | Yes     | No      | No      | This       |
   | IANA   | Re-evaluation |         |         |         | document   |
   +--------+---------------+---------+---------+---------+------------+

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 | Sub-code           | PathErr | PathErr | Reference |
   | value    | Name               | Code    | Name    |           |
   +----------+--------------------+---------+---------+-----------+
   | TBA by   | Preferable P2MP-TE | 25      | Notify  | This      |
   | IANA     | Tree Exists        |         | error   | document  |
   +----------+--------------------+---------+---------+-----------+


8.  Acknowledgments

   The authors would like to thank Loa Andersson for reviewing this
   document.














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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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