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Versions: 00 01 02 draft-ietf-pce-pcep-domain-sequence

PCE Working Group                                               D. Dhody
Internet-Draft                                                  U. Palle
Intended status: Standard              Huawei Technologies India Pvt Ltd
Expires: September 4, 2011                                 March 3, 2011


               Standard Representation Of Domain Sequence
                draft-dhody-pce-pcep-domain-sequence-00

Abstract

   The ability to compute shortest constrained Traffic Engineering Label
   Switched Paths (TE LSPs) in Multiprotocol Label Switching (MPLS) and
   Generalized MPLS (GMPLS) networks across multiple domains has been
   identified as a key requirement for P2P and P2MP scenarios.  In this
   context, a domain is a collection of network elements within a common
   sphere of address management or path computational responsibility
   such as an IGP area or an Autonomous Systems.  This document
   specifies a standard representation of domain sequence that can be
   utilized in all PCE deployment scenarios.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
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   This Internet-Draft will expire on September 4, 2011.






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Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors. All rights reserved.

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   This Internet-Draft will expire on September 2, 2011.
Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Requirements Language  . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Detail Description . . . . . . . . . . . . . . . . . . . . . .  4
     3.1.  Domains  . . . . . . . . . . . . . . . . . . . . . . . . .  4
     3.2.  Standard Representation  . . . . . . . . . . . . . . . . .  5
     3.3.  Deployment Scenarios . . . . . . . . . . . . . . . . . . .  6
       3.3.1.  Only AS  . . . . . . . . . . . . . . . . . . . . . . .  6
       3.3.2.  Only Area  . . . . . . . . . . . . . . . . . . . . . .  7
       3.3.3.  Mix of AS and Area . . . . . . . . . . . . . . . . . .  9
       3.3.4.  PCE serving multiple domains . . . . . . . . . . . . . 11
       3.3.5.  P2MP . . . . . . . . . . . . . . . . . . . . . . . . . 11
       3.3.6.  HPCE . . . . . . . . . . . . . . . . . . . . . . . . . 11
       3.3.7.  Domain Seq V/s PCE Seq . . . . . . . . . . . . . . . . 13
   4.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 14
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 14
   6.  Manageability Considerations . . . . . . . . . . . . . . . . . 14
   7.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 14
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 14
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 14




























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1.  Introduction

   RFC 5441 [A Backward-Recursive PCE-Based Computation (BRPC) Procedure
   to Compute Shortest Constrained Inter-Domain Traffic Engineering
   Label Switched Paths] mentions -

   "The sequence of domains to be traversed is either administratively
   predetermined or discovered by some means that is outside of the
   scope of this document.  The PCC MAY indicate the sequence of domains
   to be traversed using the Include Route Object (IRO) defined in
   [RFC5440] so that it is available to all PCEs."

   This document proposes a standard way to represent domain sequence
   using IRO in various deployment scenarios.

   It further gives examples of various deployment scenario including
   P2P, P2MP and HPCE.

   The domain sequence (the set of domains traversed to reach the
   destination domain) is either administratively predetermined or
   discovered by some means (H-PCE) that is outside of the scope of this
   document.  Here the focus is only on a standard representation of the
   domain sequence in all possible scenarios.

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.

   ABR:  OSPF Area Border Router.  Routers used to connect two IGP
      areas.

   AS:  Autonomous System.

   ASBR:  Autonomous System Boundary Router.

   BN:  Boundary Node, Can be an ABR or ASBR.

   BRPC:  Backward Recursive Path Computation







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   Domain:  Any collection of network elements within a common sphere of
      address management or path computational responsibility.  Examples
      of domains include Interior Gateway Protocol (IGP) areas and
      Autonomous Systems (ASs).

   Domain-Seq:  The sequence of domains for a path.

   ERO:  Explicit Route Object

   H-PCE:  Hierarchical PCE

   IGP:  Interior Gateway Protocol.  Either of the two routing
      protocols, Open Shortest Path First (OSPF) or Intermediate System
      to Intermediate System (IS-IS).

   IRO:  Include Route Object

   IS-IS:  Intermediate System to Intermediate System.

   OSPF:  Open Shortest Path First.

   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

   TE LSP:  Traffic Engineering Label Switched Path.

3.  Detail Description

3.1.  Domains

   A domain is any collection of network elements within a common sphere
   of address management or path computation responsibility.  Examples
   of domains include IGP areas or Autonomous Systems (ASes).  To
   uniquely identify a domain in the domain sequence both AS and Area-id
   is important.







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3.2.  Standard Representation

   The IRO (Include Route Object) is used to specify the domain sequence
   that the computed inter-domain path MUST traverse.

      IRO Object-Class is 10.
      IRO Object-Type is 1.


       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      //                        (Subobjects)                          //
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Sub-objects:  The IRO is made of sub-objects.
   The following sub-object types are used.
             Type   Sub-object
              32    Autonomous system number
              TBD  OSPF Area id
              TBD  ISIS Area id

   Since the length of Area-id is different for OSPF and ISIS, we
   propose different sub-objects.

   For OSPF, the area-id is a 32 bit number. The Subobject looks
       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |L|    Type     |     Length    |      Area Id (4 bytes)        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Area Id (continued)           |           Resvd               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   The length if fixed.

   For ISIS, the area-id is of variable length and thus the length of
   the Subobject is variable.  The Area-id is as described in ISIS by
   ISO standard.  The Length MUST be at least 4, and MUST be a multiple
   of 4.










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        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |L|    Type     |     Length    |                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
       //                        ISIS Area ID                         //
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

3.3.  Deployment Scenarios

3.3.1.  Only AS

   Considering each AS to be made of a single area, in this scenario the
   area MAY be skipped in the domain sequence.  The domain sequence
   could be represented with just AS numbers.

                                     +---------------------------------+
                                     |AS 200                           |
                                     |            +------+             |
                                     |            |      |             |
      +------------------------+     |            |      |   +------+  |
      | AS 100                 |     |            +------+   |      |  |
      |               +------+ |     | +------+              |      |  |
      |               |      +-+-----+-+      |              +------+  |
      |               |      | |     | |      |                        |
      |               +------+ |     | +------+                        |
      | +------+               |     |              +------+           |
      | |      |               |     |              |      |           |
      | |      |               |     |              |      |           |
      | +------+               |     |              +------+           |
      |                        |     |                                 |
      |               +------+ |     | +------+                        |
      |               |      +-+-----+-+      |               +------+ |
      |               |      | |     | |      |               |      | |
      |               +------+ |     | +------+               |      | |
      |                        |     |                        +------+ |
      |                        |     |                                 |
      |                        |     |                                 |
      |       +------+         |     |              +------+           |
      |       |      |         |     |              |      |           |
      |       |PCE   |         |     |              |PCE   |           |
      |       +------+         |     |              +------+           |
      |                        |     |                                 |
      +------------------------+     |                                 |
                                     +---------------------------------+

  Both AS are made of Area 0.



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   This could be represented as <IRO> as:

       +---------+  +---------+  +---------+
       |IRO      |  |Sub      |  |Sub      |
       |Object   |  |Object As|  |Object As|
       |Header   |  |100      |  |200      |
       |         |  |         |  |         |
       |         |  |         |  |         |
       +---------+  +---------+  +---------+



       +---------+  +---------+  +---------+  +---------+  +---------+
       |IRO      |  |Sub      |  |Sub      |  |Sub      |  |Sub      |
       |Object   |  |Object As|  |Object   |  |Object As|  |Object   |
       |Header   |  |100      |  |Area 0   |  |200      |  |Area 0   |
       |         |  |         |  |         |  |         |  |         |
       |         |  |         |  |         |  |         |  |         |
       +---------+  +---------+  +---------+  +---------+  +---------+
   Area is optional and it MAY be skipped.  PCE should be able to
   understand both notations.

3.3.2.  Only Area

   Consider a case where both end of LSP belong to different area but
   within the same AS, this could be represented in domain sequence
   using the AREA sub-object.  AS number MAYBE skipped.
























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 +-------------------+                            +-------------------+
 |                   |                            |                   |
 |           +--+    |                            |     +--+          |
 |  +--+     |  |    |                            |     |  |          |
 |  |  |     +--+    |                            |     +--+   +--+   |
 |  +--*             +                            +            |  |   |
 |                   |                            |            +--+   |
 |         *--+      +                            +                   |
 |         |  |      |                            |     +--+          |
 |         +--+      |                            |     |  |          |
 |                   |+--------------------------+|     +--+          |
 |                  ++++                       +-++                   |
 |                  ||||         +--+          | ||                   |
 | Area 2           ++++         |  |          +-++  Area 4           |
 +-------------------+|          +--+            |+-------------------+
                      |                          |
                      |                +--+      |
                      |    +--+        |  |      |
                      |    |  |        +--+      |
                      |    +--+                  |
                      |                          |
                      |                          |
                      |                          |
                      |                          |
                      |           +--+           |
                      |           |  |           |
                      |           +--+           |
  +------------------+|                          |+--------------------+
  |                  ++-+                      +-++                    |
  |                  || |                      | ||                    |
  |                  ++-+    Area 0            +-++                    |
  |                  |+--------------------------+|     +--+           |
  |          +--+    |                            |     |  |           |
  |          |  |    |                            |     +--+           |
  | +--+     +--+    |                            |                    |
  | |  |             +                            +            +--+    |
  | +--+             |                            |            |  |    |
  |                  +                            +            +--+    |
  |       +--+       |                            |                    |
  |       |  |       |                            |     +--+           |
  |       +--+       |                            |     |  |           |
  |                  |                            |     +--+           |
  |                  |                            |                    |
  | Area 1           |                            |  Area 5            |
  +------------------+                            +--------------------+

AS Number is 100.




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   This could be represented as <IRO> as:

     +---------+ +---------+ +---------+ +---------+
     |IRO      | |Sub      | |Sub      | |Sub      |
     |Object   | |Object   | |Object   | |Object   |
     |Header   | |Area 2   | |Area 0   | |Area 4   |
     |         | |         | |         | |         |
     |         | |         | |         | |         |
     +---------+ +---------+ +---------+ +---------+


     +---------+ +---------+ +---------+ +---------+ +---------+
     |IRO      | |Sub      | |Sub      | |Sub      | |Sub      |
     |Object   | |Object As| |Object   | |Object   | |Object   |
     |Header   | |100      | |Area 2   | |Area 0   | |Area 4   |
     |         | |         | |         | |         | |         |
     |         | |         | |         | |         | |         |
     +---------+ +---------+ +---------+ +---------+ +---------+

   AS is optional and it MAY be skipped.  PCE should be able to
   understand both notations.

3.3.3.  Mix of AS and Area

   In inter-AS case where an AS is further made up of multiple areas,
   both AS number and area should be a part of domain sequence.

























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                  |
                  |  +-------------+                +----------------+
                  |  |Area 2       |                |Area 4          |
                  |  |         +--+|                |          +--+  |
                  |  |         |  ||                |          |  |  |
                  |  |  +--+   +--+|                |   +--+   +--+  |
                  |  |  |  |       |                |   |  |         |
                  |  |  *--+       |                |   +--+         |
                  |  | /      +--+ |                |          +--+  |
                  |  |/       |  | |                |          |  |  |
                  |  /        +--+ |                |   +--+   +--+  |
                  | /|  +--+       |+--------------+|   |  |         |
                  |/ |  |  |       ++-+          +-++   +--+         |
   +-------------+/  |  +--+       || |          | ||                |
   |             /|  |             ++-+          +-++                |
   |         +--*||  +-------------+|              |+----------------+
   |         |  |||                 |     +--+     |
   |         +--+||                 |     |  |     |
   |    +--+     ||                 |     +--+     |
   |    |  |     ||                 |              |
   |    +--+     ||                 |              |
   |             ||                 |     +--+     |
   |+--+         ||                 |     |  |     |
   ||  |         ||                 |     +--+     |
   |+--+         ||                 |              |
   |             ||                 |     +--+     |
   |    +--+     ||  +------------+ |     |  |     |+----------------+
   |    |  |     ||  |Area 3      +-++    +--+   +-++ Area 5         |
   |    +--+     ||  |            | ||           | ||                |
   |             ||  |            +-++           +-++                |
   |         +--+||  |       +--+ | |  Area 0      ||   +--+         |
   |         |  |||  |       |  | | +--------------+|   |  |         |
   |         +--*||  |       +--+ |                 |   +--+         |
   |             \|  |            |                 |          +--+  |
   |Area 1       |\  |   +--+     |                 |   +--+   |  |  |
   +-------------+|\ |   |  |     |                 |   |  |   +--+  |
                  | \|   +--+  +--+                 |   +--+         |
                  |  \         |  |                 |                |
                  |  |\        +--+                 |          +--+  |
                  |  | \ +--+     |                 |          |  |  |
                  |  |  \|  |     |                 |          +--+  |
                  |  |   *--+     |                 |                |
                  |  |            |                 |                |
                  |  +------------+                 +----------------+
                  |
                  |
       As 100     |  AS 200
                  |



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The domain sequence can be carried in IRO as shown below:

 +-------+ +-------+ +-------+ +-------+ +-------+ +-------+ +-------+
 |IRO    | |Sub    | |Sub    | |Sub    | |Sub    | |Sub    | |Sub    |
 |Object | |Object | |Object | |Object | |Object | |Object | |Object |
 |Header | |As 100 | |Area 1 | |AS 200 | |Area 3 | |Area 0 | |Area 4 |
 |       | |       | |       | |       | |       | |       | |       |
 +-------+ +-------+ +-------+ +-------+ +-------+ +-------+ +-------+
Combination of both AS and Area uniquely identify a domain in the domain
sequence.

3.3.4.  PCE serving multiple domains

   A single PCE maybe responsible for multiple domains; for example PCE
   function deployed on an ABR.  Domain sequence should have no impact
   on this.  PCE which can support 2 adjacent domains can internally
   handle this situation without any impact on the neighboring domains.

3.3.5.  P2MP

   In case of P2MP the path domain tree is nothing but a series of
   Domain-Seq, as shown in the below figure:

      D1-D3-D6, D1-D3-D5 and D1-D2-D4.
                  D1
                 /  \
                D2  D3
               /   /  \
              D4  D5  D6

   The same domain sequence are carried in IRO as explained above.

3.3.6.  HPCE

   Consider a case as shown below consisting of child and parent PCE.
















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                                +--------+
                                | Parent |
                                | PCE    |
                                +--------+

 +-------------------+                            +-------------------+
 |           +--+    |                            |     +--+          |
 |  +--+     |  |    |                            |     |  |          |
 |  |  |     +--+    |                            |     +--+   +--+   |
 |  +--*             +                            +            |  |   |
 |                   |                            |            +--+   |
 |         *--+      +                            +                   |
 |         |  |      |                            |     +--+          |
 |         +--+      |                            |     |  |          |
 |                   |+--------------------------+|     +--+          |
 |                  ++++                       +-++                   |
 |                  ||||         +--+          | ||                   |
 | Area 2           ++++         |  |          +-++  Area 4           |
 +-------------------+|          +--+            |+-------------------+
                      |                +--+      |
                      |    +--+        |  |      |
                      |    |  |        +--+      |
                      |    +--+                  |
                      |                          |
                      |           +--+           |
                      |           |  |           |
                      |           +--+           |
  +------------------+|                          |+--------------------+
  |                  ++-+                      +-++                    |
  |                  || |                      | ||                    |
  |                  ++-+    Area 0            +-++                    |
  |                  |+--------------------------+|     +--+           |
  |          +--+    |                            |     |  |           |
  |          |  |    |                            |     +--+           |
  | +--+     +--+    |                            |                    |
  | |  |             +                            +            +--+    |
  | +--+             |                            |            |  |    |
  |                  +                            +            +--+    |
  |       +--+       |                            |                    |
  |       |  |       |                            |     +--+           |
  |       +--+       |                            |     |  |           |
  |                  |                            |     +--+           |
  | Area 1           |                            |  Area 5            |
  +------------------+                            +--------------------+

   In HPCE implementation PCE(1) can request the parent PCE to determine
   the domain path and return in the PCRep in form of ERO.  The
   Subobject would be AS and Area (OSPF/ISIS).  So in this case, the



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   reply would carry the result as



     +---------+ +---------+ +---------+ +---------+
     |ERO      | |Sub      | |Sub      | |Sub      |
     |Object   | |Object   | |Object   | |Object   |
     |Header   | |Area 2   | |Area 0   | |Area 4   |
     |         | |         | |         | |         |
     |         | |         | |         | |         |
     +---------+ +---------+ +---------+ +---------+


     +---------+ +---------+ +---------+ +---------+ +---------+
     |ERO      | |Sub      | |Sub      | |Sub      | |Sub      |
     |Object   | |Object As| |Object   | |Object   | |Object   |
     |Header   | |100      | |Area 2   | |Area 0   | |Area 4   |
     |         | |         | |         | |         | |         |
     |         | |         | |         | |         | |         |
     +---------+ +---------+ +---------+ +---------+ +---------+

3.3.7.  Domain Seq V/s PCE Seq

   [PCE-P2MP-PROCEDURES] introduces the concept of PCE-Sequence, where a
   sequence of PCE based on the domain sequence should be decided and
   attached in the PCReq at the very beginning of path computation.  It
   is much simpler and advantageous to carry only domain-sequence rather
   than PCE-Sequence.

   Advantages

   o  All PCE must be aware of all other PCEs in all domain for PCE-
      Sequence.  There is no clear method for this.  In domain-sequence
      PCE should be aware of the domains and not all the PCEs serving
      the domain.  PCE needs to be aware of the neighboring PCEs as done
      by discovery protocols.

   o  There maybe multiple PCE in a domain, the selection of PCE
      shouldn't be made at the PCC/PCE(1).  This decision is made only
      at the neighboring PCE which is completely aware of states of PCE
      via notification messages.

   o  Domain sequence would be compatible to P2P inter-domain BRPC
      method as described in RFC 5441.

   There is no need for PCE-Sequence and it doesn't give any benefits
   over Domain Seq.




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4.  IANA Considerations

   IANA has defined a registry for OSPF and ISIS Area sub-object.

              Type   Sub-object
              TBD    OSPF Area id
              TBD    ISIS Area id

5.  Security Considerations

   This document specifies a standard representation of domain sequence,
   which is used in all inter-domain PCE scenarios as explained in other
   RFC and drafts.  It does not introduce any new security
   considerations.

6.  Manageability Considerations

   TBD

7.  Acknowledgments

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

8.  References

8.1.  Normative References

   [ISO]                 "Intermediate System to Intermediate System
                         Intra-Domain Routeing Exchange Protocol for
                         use in Conjunction with the Protocol for
                         Providing the Connectionless-mode Network
                         Service" ISO/IEC 10589:2002 Second Edition

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

8.2.  Informative References

   [PCE-HIERARCHY-FWK]    King, D. and A. Farrel, "The Application of
                          the Path Computation Element Architecture to
                          the Determination of a Sequence of Domains in
                          MPLS and GMPLS", September 2010.

   [PCE-P2MP-PROCEDURES]  Zhao, Q., Ali, Z., Saad,, T., and D. King,
                          "PCE-based Computation Procedure To Compute
                          Shortest Constrained P2MP Inter-domain Traffic




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                          Engineering Label Switched Paths",
                          January 2011.

   [RFC5440]              Ayyangar, A ., Farrel, A ., Oki, E., Atlas,
                          A., Dolganow, A., Ikejiri, Y., Kumaki, K.,
                          Vasseur, J., and J. Roux, "Path Computation
                          Element (PCE) communication Protocol (PCEP)",
                          March 2009.

   [RFC5441]              Vasseur, JP., Zhang, R., Bitar, N., and JL. Le
                          Roux, "A Backward-Recursive PCE-Based
                          Computation (BRPC) Procedure to Compute
                          Shortest Constrained Inter-Domain Traffic
                          Engineering Label Switched Paths", April 2009.

Authors' Addresses

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

   EMail: dhruvd@huawei.com


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

   EMail: udayasreepalle@huawei.com

























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