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PCE Working Group                                               D. Dhody
Internet-Draft                                                  U. Palle
Intended status: Experimental              Huawei Technologies India Pvt
Expires: February 18, 2013                                           Ltd
                                                         August 17, 2012


  Supporting explicit-path per destination in Path Computation Element
        Communication Protocol (PCEP) P2MP Path Request Message.
              draft-dhody-pce-pcep-p2mp-per-destination-02

Abstract

   The ability to determine paths of point-to-multipoint (P2MP)
   Multiprotocol Label Switching (MPLS) and Generalized MPLS (GMPLS)
   Traffic Engineering Label Switched Paths (TE LSPs) is one the key
   requirements for Path Computation Element (PCE).  [RFC6006] and
   [PCE-P2MP-PROCEDURES] describes these mechanisms for intra and inter
   domain environment.

   Explicit Path in this document refers to the configured list of
   network elements that MUST be traversed or MUST be excluded in the
   final path computation.  This should not be confused with the RSVP
   terminology.  Network elements can further be strict or loose hop.

   This document describes extensions to the PCE communication Protocol
   (PCEP) to define explicit-path per destination in P2MP context.

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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   Internet-Drafts are draft documents valid for a maximum of six months
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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."

   This Internet-Draft will expire on February 18, 2013.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the



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   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.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Requirements Language  . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Need to Define Explicit Path Per Destination . . . . . . . . .  4
     3.1.  Inter Domain P2MP Path Computation . . . . . . . . . . . .  4
     3.2.  Intra Domain P2MP Path Computation . . . . . . . . . . . .  6
     3.3.  Backward Compatibility . . . . . . . . . . . . . . . . . .  8
   4.  Detailed Description . . . . . . . . . . . . . . . . . . . . .  8
     4.1.  Objective  . . . . . . . . . . . . . . . . . . . . . . . .  8
     4.2.  Request Message Format . . . . . . . . . . . . . . . . . .  8
     4.3.  Ordering Destinations in END-POINTS Objects  . . . . . . .  9
       4.3.1.  Example  . . . . . . . . . . . . . . . . . . . . . . . 10
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   7.  Manageability Considerations . . . . . . . . . . . . . . . . . 12
     7.1.  Control of Function and Policy . . . . . . . . . . . . . . 12
     7.2.  Information and Data Models  . . . . . . . . . . . . . . . 13
     7.3.  Liveness Detection and Monitoring  . . . . . . . . . . . . 13
     7.4.  Verify Correct Operations  . . . . . . . . . . . . . . . . 13
     7.5.  Requirements On Other Protocols  . . . . . . . . . . . . . 13
     7.6.  Impact On Network Operations . . . . . . . . . . . . . . . 13
   8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 13
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 13
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 13












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1.  Introduction

   The Path Computation Element (PCE) architecture is defined in
   [RFC4655].  [RFC5862] mentions a P2MP PCE MUST be able to provide to
   the path computation a limiting set of nodes that can be used as
   branches for a P2MP path computation, or to provide a list of nodes
   that must not be used as branch points.  This document mention the
   need to specify the branch points (or explict path) per destination.

   [RFC6006] describe a PCE-based path computation procedure to compute
   optimal constrained (G)MPLS P2MP TE LSPs.  It also defines the format
   of path request message used in P2MP, which limits explicit path in
   form of IRO/XRO; to be applied to full P2MP tunnel and thus to only
   the common path to all leaves.

   This document describes the need for supporting explicit-path per
   destination in intra and inter-domain P2MP scenario.  It further
   lists the path request format and mode of operations

1.1.  Requirements Language

   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].

2.  Terminology

   The following terminology is used in this document.

   Explicit-Path:  Set of network elements configured by the
      administrator that MUST be traversed or MUST be excluded.

   IRO:  Include Route Object.

   PCC:  Path Computation Client: any client application requesting a
      path computation to be performed by a Path Computation Element.

   PCE:  Path Computation Element.  An entity (component, application,
      or network node) that is capable of computing a network path or
      route based on a network graph and applying computational
      constraints.

   P2MP:  Point-to-Multipoint

   P2P:  Point-to-Point






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   RRO:  Record Route Object

   RSVP:  Resource Reservation Protocol

   TE LSP:  Traffic Engineering Label Switched Path.

   XRO:  Exclude Route Object.

3.  Need to Define Explicit Path Per Destination

3.1.  Inter Domain P2MP Path Computation

   In the Figure 1 below, D1 is the root domain; D5 and D6 are the
   destination domains.





































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                    |
                    |  +-------------+                +----------------+
                    |  |D 3          |                |D 6             |
                    |  |         +--+|                |          +--+  |
                    |  |         |  ||                |          |  |  |
                    |  |  +--+   +--+|                |   +--+   +--+  |
                    |  |  |  |       |                |   |  |         |
                    |  |  *--+       |                |   +--+         |
                    |  | /      +--+ |                |          +--+  |
                    |  |/       |  | |                |          |  |  |
                    |  /        +--+ |                |   +--+   +--+  |
                    | /|  +--+       |+--------------+|   |  |         |
                    |/ |  |  |       ++-+          +-++   +--+         |
     +-------------+/  |  +--+       || |          | ||                |
     |             /|  |             ++-+          +-++                |
     |         +--*||  +-------------+|              |+----------------+
     |         |  |||                 |     +--+     |
     |         +--+||                 |     |  |     |
     |    +--+     ||                 |     +--+     |
     |    |  |     ||                 |              |
     |    +--+     ||                 |              |
     |             ||                 |     +--+     |
     |+--+         ||                 |     |  |     |
     ||  |         ||                 |     +--+     |
     |+--+         ||                 |              |
     |             ||                 |     +--+     |
     |    +--+     ||  +------------+ |     |  |     |+----------------+
     |    |  |     ||  |D 2         +-++    +--+   +-++ D 5            |
     |    +--+     ||  |            | ||           | ||                |
     |             ||  |            +-++           +-++                |
     |         +--+||  |       +--+ | |  D 4         ||   +--+         |
     |         |  |||  |       |  | | +--------------+|   |  |         |
     |         +--*||  |       +--+ |                 |   +--+         |
     |             \|  |            |                 |          +--+  |
     |D 1          |\  |   +--+     |                 |   +--+   |  |  |
     +-------------+|\ |   |  |     |                 |   |  |   +--+  |
                    | \|   +--+  +--+                 |   +--+         |
                    |  \         |  |                 |                |
                    |  |\        +--+                 |          +--+  |
                    |  | \ +--+     |                 |          |  |  |
                    |  |  \|  |     |                 |          +--+  |
                    |  |   *--+     |                 |                |
                    |  |            |                 |                |
                    |  +------------+                 +----------------+
                    |
                    |
         As 100     |  AS 200
                    |



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                     Figure 1: Domain Topology Example

   [PCE-P2MP-PROCEDURES] defines inter-domain P2MP path computation
   procedure and assumes that the sequence of domains for a path (the
   path domain tree) will be known in advance due to deployment and
   commercial limitations (e.g., inter-AS peering agreements).  In the
   Figure 2 below, the P2MP tree spans 5 domains.  Destination in D6
   would use the domain-sequence: D1-D3-D4-D6; and destination in D5
   would use the domain-sequence: D1-D3-D4-D5.


                               D3    D6
                              /  \  /
                             D1   D4
                                    \
                                     D5

                      Figure 2: Domain Sequence Tree

   Since different destinations will have different domain sequence
   within the domain tree, it requires domain-sequence to be encoded in
   form of IRO to be attached per destination.  It cannot be encoded for
   all destinations.

   Thus domain-sequence encoded in form IRO (as per [DOMAIN-SEQ]) should
   be attached to destinations and not attached to full P2MP tree.

3.2.  Intra Domain P2MP Path Computation

   Administrator at the source can exert stronger control by providing
   explicit path (include, exclude, loose etc) per destination.

   In Figure 3 shows the common path over which a common explicit path
   in form of IRO and/or XRO can be set.

















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                                           +---+
                                           | F |
                                          /*---+
                                        //
                                      //
                                    //
                                  //
        +---+  +---+  +---+  +---*         +---+
        | A +--+ B +--+ C +--+ D +---------+ E |
        +---+  +---+  +---+  +---*\        +---+
        |                        | \\
        |                        |   \\
        |                        |     \\
        |                        |       \\
        |<-----common path------>|         *---+
        |                        |         | G |
        |                        |         +---+
          Explicit Path Here

                             Figure 3: Example

   But as shown in Figure 4, once new destinations are added and branch
   points are much nearer to ingress causing common path to reduce, the
   administrator would not be able to apply the explicit path as before.


                           +---+           +---+
                           | H |           | F |
                           *---+          /*---+
                         //             //
                       //             //
                      /             //
                    //            //
        +---+  +---*  +---+  +---*         +---+
        | A +--+ B +--+ C +--+ D +---------+ E |
        +---+  +---+  +---*  +---*\        +---+
        |          |       \\      \\
        |          |         \\      \\
        |<-------->|           \\      \\
        | Common   |            \\      \\
        |  path    |               *---+   *---+
        |          |               | I |   | G |
        |          |               +---+   +---+
        |          |
        |          |

                             Figure 4: Example




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3.3.  Backward Compatibility

   Basic MPLS TE P2MP Tunnel configurations for various operators
   support the configuration of explicit-path per destination.  In some
   operators where preconfigured path must be setup, during
   configurations the path to each destination is configured as an
   explicit path and attached to each destination.

   It makes sense to apply explict path per destination instead of the
   full P2MP tree.

4.  Detailed Description

4.1.  Objective

   [RFC6006] defines Request Message Format and Objects, along with
   <end-point-rro-pair-list>.  This section introduce the concept of
   <iro-list>, <xro-list> and <metric-list> which are added to the <end-
   point-rro-pair-list> to support 'per destination'.

   Use of <iro-list>, <xro-list> to carry explicit-path per destination
   in intra-domain scenario.

   Use of <iro-list> to carry domain-sequence per destination in inter-
   domain scenario.

   Use of <metric-list> to carry metric value of each calculated path
   encoded in <rro-list>.  In case of reoptimization of a P2MP tree,
   each calculated S2L path MUST be accompanied by metric value.

4.2.  Request Message Format

   To carry explicit path for each destination, <END-POINTS> objects
   need to be ordered and grouped in a way such that IRO object, XRO
   object, RRO object and METRIC object can be associated with each
   destination.















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           The format of PCReq message is modified as follows:

           <PCReq Message>::= <Common Header>
                              <request>
           where:
           <request>::= <RP>
                        <end-point-iro-xro-rro-metric-list>
                        [<OF>]
                        [<LSPA>]
                        [<BANDWIDTH>]
                        [<metric-list>]
                        [<IRO>]
                        [<LOAD-BALANCING>]

           where:
           <end-point-iro-xro-rro-metric-list> ::=
                        <END-POINTS>
                        [<IRO-List>]
                        [<XRO-List>]
                        [<RRO-List>]
                        [<metric-list>]
                        [<end-point-iro-xro-rro-metric-list >]


           <RRO-List>::=<RRO>[<BANDWIDTH>][<RRO-List>]
           <metric-list>::=<METRIC>[<metric-list>]
           <IRO-List>::=<IRO>[<IRO-List>]
           <XRO-List>::=<XRO>[<XRO-List>]

   From [RFC6006] usage of <end-point-rro-pair-list> is changed to <end-
   point-iro-xro-rro-metric-list> in this document.

   Note that the new format is backward compatible to [RFC6006] format.

4.3.  Ordering Destinations in END-POINTS Objects

   Multiple destinations are encoded into a single ENDPOINTS object,
   Each Endpoint maybe followed by multiple lists of IROs, XROs, RROs or
   METRICs.  The first <IRO> object would belong to the first
   destination, the second <IRO> object to the second destination and
   hence forth.  The first <XRO> object would belong to the first
   destination, the second <XRO> object to the second destination and
   hence forth...

   Note that a destination (P2MP tree leaf) MAY have






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   o  both <IRO> and <XRO>

   o  <IRO> only

   o  <XRO> only

   o  No explicit path

   To maintain the ordering between the destination and objects in the
   list, there MAYBE a need to divide a set of destinations into
   multiple ENDPOINTS, this explained in below example.

4.3.1.  Example

   Destination 1 has include IRO1 and exclude XRO1

   Destination 2 has only include IRO2

   Destination 3 has only exclude XRO3

   Destination 4 has only exclude XRO4

   Destination 5 has none

   Here if we try to encode all destinations in one <ENDPOINT> and
   objects in list, we will not map XRO3 to destination 3, the rule is
   to map sequentially and thus XRO3 will belong to destination 2.

   To avoid this we must break the set of destinations into two sets as
   shown below





















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                     +-----------------------------+
                     |           Leaf Type         |
                     +-----------------------------+
                     |           Source IP         |
                     +-----------------------------+
            +------> |         Destination 1       |   <ENDPOINT>
            |        +-----------------------------+
            |    +-> |         Destination 2       |
            |    *   +-----------------------------+
            |    *   |         Destination 5       |
            |    *   +-----------------------------+
            |    *
            |    *   +-----------------------------+
            +----*-> |             IRO1            |
            |    *   +-----------------------------+
            |    *   |            HOPI 1-1         |
            |    *   +-----------------------------+
            |    *   |             ....            |   <IRO-List>
            |    *   +-----------------------------+   with 2 IRO1, IRO2
            |    +-> |              IRO2           |
            |        +-----------------------------+
            |        |            HOPI 2-1         |
            |        +-----------------------------+
            |        |             ....            |
            |        +-----------------------------+
            |
            |        +-----------------------------+
            +----->  |             XRO1            |
                     +-----------------------------+  <XRO-List>
                     |            HOPX 1-1         |  with 1 XRO1
                     +-----------------------------+
                     |             ....            |
                     +-----------------------------+

   ENDPOINT1 carries destination 1, 2 and 5 and corresponding <iro-list>
   and <xro-list>.  Here Destination 1 has IRO1 and XRO1; Destination 2
   has IRO2; and Destination 5 has none.














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                     +-----------------------------+
                     |           Leaf Type         |
                     +-----------------------------+
                     |           Source IP         |
                     +-----------------------------+
            +------> |         Destination 3       |   <ENDPOINT>
            |        +-----------------------------+
            |    +-> |         Destination 4       |
            |    *   +-----------------------------+
            |    *
            |    *   +-----------------------------+
            +----*-> |             XRO3            |
                 *   +-----------------------------+
                 *   |            HOPX 3-1         |
                 *   +-----------------------------+
                 *   |             ....            |   <XRO-List>
                 *   +-----------------------------+   with 2 XRO3, XRO4
                 +-> |              XRO4           |
                     +-----------------------------+
                     |            HOPX 4-1         |
                     +-----------------------------+
                     |             ....            |
                     +-----------------------------+

   ENDPOINT2 carries destination 3 and 4 and corresponding <xro-list>
   only.  Here destination 3 maps to XRO3 and Destination 4 to XRO4.

5.  IANA Considerations

   TBD

6.  Security Considerations

   PCEP security mechanisms as described in [RFC6006] and
   [PCE-P2MP-PROCEDURES] are applicable for this document.  This
   document does not add any new security threat.

7.  Manageability Considerations

7.1.  Control of Function and Policy

   Mechanisms defined in this document do not add any new control
   function/policy requirements in addition to those already listed in
   [RFC6006].







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7.2.  Information and Data Models

   Mechanisms defined in this document do not imply any new MIB
   requirements in addition to those already listed in [PCE-P2MP-MIB].

7.3.  Liveness Detection and Monitoring

   Mechanisms defined in this document do not imply any new liveness
   detection and monitoring requirements in addition to those already
   listed in [RFC6006].

7.4.  Verify Correct Operations

   Mechanisms defined in this document do not imply any new operation
   verification requirements in addition to those already listed in
   [RFC6006].

7.5.  Requirements On Other Protocols

   Mechanisms defined in this document do not imply any requirements on
   other protocols in addition to those already listed in [RFC6006].

7.6.  Impact On Network Operations

   Mechanisms defined in this document do not have any impact on network
   operations in addition to those already listed in [RFC6006].

8.  Acknowledgments

   We would like to thank Pradeep Shastry, Suresh babu, Quintin Zhao,
   Daniel King and Chen Huaimo for their useful comments and
   suggestions.

9.  References

9.1.  Normative References

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

9.2.  Informative References

   [RFC4655]              Farrel, A., Vasseur, J., and J. Ash, "A Path
                          Computation Element (PCE)-Based Architecture",
                          RFC 4655, August 2006.

   [RFC5862]              Yasukawa, S. and A. Farrel, "Path Computation



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                          Clients (PCC) - Path Computation Element (PCE)
                          Requirements for Point-to-Multipoint MPLS-TE",
                          RFC 5862, June 2010.

   [RFC6006]              Zhao, Q., King, D., Verhaeghe, F., Takeda, T.,
                          Ali, Z., and J. Meuric, "Extensions to the
                          Path Computation Element Communication
                          Protocol (PCEP) for Point-to-Multipoint
                          Traffic Engineering Label Switched Paths",
                          RFC 6006, September 2010.

   [PCE-P2MP-PROCEDURES]  Zhao, Q., Dhody, D., Ali, Z., Saad,, T.,
                          Sivabalan,, S., and R. Casellas, "PCE-based
                          Computation Procedure To Compute Shortest
                          Constrained P2MP Inter-domain Traffic
                          Engineering Label Switched Paths (draft-ietf-
                          pce-pcep-inter-domain-p2mp-procedures-02)",
                          May 2012.

   [PCE-P2MP-MIB]         Zhao, Q., Dhody, D., Palle, U., and D. King,
                          "Management Information Base for the PCE
                          Communications Protocol (PCEP) When Requesting
                          Point-to-Multipoint Services
                          (draft-zhao-pce-pcep-p2mp-mib-05)",
                          August 2012.

   [DOMAIN-SEQ]           Dhody, D., Palle, U., and R. Casellas,
                          "Standard Representation Of Domain Sequence
                          (draft-ietf-pce-pcep-domain-sequence-01)",
                          July 2012.

Authors' Addresses

   Dhruv Dhody
   Huawei Technologies India Pvt Ltd
   Leela Palace
   Bangalore, Karnataka  560008
   INDIA

   EMail: dhruv.dhody@huawei.com











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   Udayasree Palle
   Huawei Technologies India Pvt Ltd
   Leela Palace
   Bangalore, Karnataka  560008
   INDIA

   EMail: udayasree.palle@huawei.com












































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