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Versions: (draft-dhody-pce-pcep-domain-sequence) 00 01 02 03 04 05 06 07 08 09 10 11 12 RFC 7897

PCE Working Group                                               D. Dhody
Internet-Draft                                                  U. Palle
Intended status: Experimental                        Huawei Technologies
Expires: July 11, 2014                                       R. Casellas
                                                                    CTTC
                                                         January 7, 2014


               Standard Representation Of Domain-Sequence
                 draft-ietf-pce-pcep-domain-sequence-04

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.  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 Interior
   Gateway Protocol (IGP) area or an Autonomous Systems (AS).  This
   document specifies a standard representation and encoding of a
   Domain-Sequence, which is defined as an ordered sequence of domains
   traversed to reach the destination domain to be used by Path
   Computation Elements (PCEs) to compute inter-domain shortest
   constrained paths across a predetermined sequence of domains . This
   document also defines new subobjects to be used to encode domain
   identifiers.

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."

   This Internet-Draft will expire on July 11, 2014.







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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
   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 . . . . . . . . . . . . . . . . . .   4
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Detail Description  . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  Domains . . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.2.  Domain-Sequence . . . . . . . . . . . . . . . . . . . . .   5
     3.3.  Standard Representation . . . . . . . . . . . . . . . . .   6
     3.4.  Include Route Object (IRO)  . . . . . . . . . . . . . . .   7
       3.4.1.  Subobjects  . . . . . . . . . . . . . . . . . . . . .   7
       3.4.2.  Option (A): New IRO Object Type . . . . . . . . . . .   9
         3.4.2.1.  Handling of the Domain-Sequence IRO object  . . .  11
       3.4.3.  Option B: Existing IRO Object Type  . . . . . . . . .  12
       3.4.4.  Comparison  . . . . . . . . . . . . . . . . . . . . .  13
     3.5.  Exclude Route Object (XRO)  . . . . . . . . . . . . . . .  14
       3.5.1.  Subobjects  . . . . . . . . . . . . . . . . . . . . .  14
         3.5.1.1.  Autonomous system . . . . . . . . . . . . . . . .  14
         3.5.1.2.  IGP Area  . . . . . . . . . . . . . . . . . . . .  15
     3.6.  Explicit Exclusion Route Subobject (EXRS) . . . . . . . .  16
     3.7.  Explicit Route Object (ERO) . . . . . . . . . . . . . . .  17
   4.  Other Considerations  . . . . . . . . . . . . . . . . . . . .  17
     4.1.  Inter-Area Path Computation . . . . . . . . . . . . . . .  18
     4.2.  Inter-AS Path Computation . . . . . . . . . . . . . . . .  20
       4.2.1.  Example 1 . . . . . . . . . . . . . . . . . . . . . .  20
       4.2.2.  Example 2 . . . . . . . . . . . . . . . . . . . . . .  22
     4.3.  Boundary Node and Inter-AS-Link . . . . . . . . . . . . .  24
     4.4.  PCE Serving multiple Domains  . . . . . . . . . . . . . .  24
     4.5.  P2MP  . . . . . . . . . . . . . . . . . . . . . . . . . .  25
     4.6.  Hierarchical PCE  . . . . . . . . . . . . . . . . . . . .  25
     4.7.  Relationship to PCE Sequence  . . . . . . . . . . . . . .  27
     4.8.  Relationship to RSVP-TE . . . . . . . . . . . . . . . . .  27
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  28



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     5.1.  PCEP Objects  . . . . . . . . . . . . . . . . . . . . . .  28
     5.2.  New Subobjects  . . . . . . . . . . . . . . . . . . . . .  28
     5.3.  Error Object Field Values . . . . . . . . . . . . . . . .  28
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  29
   7.  Manageability Considerations  . . . . . . . . . . . . . . . .  29
     7.1.  Control of Function and Policy  . . . . . . . . . . . . .  29
     7.2.  Information and Data Models . . . . . . . . . . . . . . .  29
     7.3.  Liveness Detection and Monitoring . . . . . . . . . . . .  29
     7.4.  Verify Correct Operations . . . . . . . . . . . . . . . .  29
     7.5.  Requirements On Other Protocols . . . . . . . . . . . . .  30
     7.6.  Impact On Network Operations  . . . . . . . . . . . . . .  30
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  30
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  30
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  30
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  30

1.  Introduction

   A PCE may be used to compute end-to-end paths across multi-domain
   environments using a per-domain path computation technique [RFC5152].
   The so called backward recursive path computation (BRPC) mechanism
   [RFC5441] defines a PCE-based path computation procedure to compute
   inter-domain constrained (G)MPLS TE LSPs.  However, both per-domain
   and BRPC techniques assume that the sequence of domains to be crossed
   from source to destination is known, either fixed by the network
   operator or obtained by other means.  Also for inter-domain point-to-
   multi-point (P2MP) tree computation, [PCE-P2MP-PROCEDURES] assumes
   the domain-tree is known in priori.

   The list of domains (domain-sequence) in a point-to-point (P2P) path
   or a point-to-multi-point (P2MP) tree is usually a constraint in the
   path computation request.  The PCE determines the next PCE to forward
   the request based on the domain-sequence.  In a multi-domain path
   computation, a PCC MAY indicate the sequence of domains to be
   traversed using the Include Route Object (IRO) defined in [RFC5440].

   When the sequence of domains is not known in advance, the
   Hierarchical PCE (H-PCE) [RFC6805] architecture and mechanisms can be
   used to determine the end-to-end Domain-Sequence.

   This document defines a standard way to represent and encode a
   Domain-Sequence in various deployment scenarios including P2P, P2MP
   and H-PCE.

   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.



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   [RFC5440] defines the Include Route Object (IRO) and the Explicit
   Route Object (ERO); [RFC5521] defines the Exclude Route Object (XRO)
   and the Explicit Exclusion Route Subobject (EXRS); The use of
   Autonomous System (AS) (albeit with a 2-Byte AS number) as an
   abstract node representing domain is defined in [RFC3209], this
   document specifies new subobjects to include or exclude domains such
   as an IGP area or an Autonomous Systems (4-Byte as per [RFC4893]).

   Further, the domain identifier may simply act as delimiter to specify
   where the domain boundary starts and ends.

   This is a companion document to Resource ReserVation Protocol -
   Traffic Engineering (RSVP-TE) extensions for the domain identifiers
   [DOMAIN-SUBOBJ].

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

   Domain:  As per [RFC4655], 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-Sequence:  An ordered sequence of domains traversed to reach
      the destination domain.

   ERO:  Explicit Route Object

   H-PCE:  Hierarchical PCE




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   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

   RSVP:  Resource Reservation Protocol

   TE LSP:  Traffic Engineering Label Switched Path.

3.  Detail Description

3.1.  Domains

   [RFC4726] and [RFC4655] define domain as a separate administrative or
   geographic environment within the network.  A domain may be further
   defined as a zone of routing or computational ability.  Under these
   definitions a domain might be categorized as an AS or an IGP area.
   Each AS can be made of several IGP areas.  In order to encode a
   Domain-Sequence, it is required to uniquely identify a domain in the
   Domain-Sequence.  A domain can be uniquely identified by area-id or
   AS or both.

3.2.  Domain-Sequence

   A domain-sequence is an ordered sequence of domains traversed to
   reach the destination domain.

   A domain-sequence can be applied as a constraint and carried in path
   computation request to PCE(s).  A domain-sequence can also be the
   result of a path computation.  For example, in the case of H-PCE




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   [RFC6805] Parent PCE MAY send the Domain-Sequence as a result in a
   path computation reply.

   In this context, the ordered nature of a domain-sequence is
   considered to be important.  In a P2P path, the domains listed appear
   in the order that they are crossed.  In a P2MP path, the domain tree
   is represented as list of domain sequences.

   A domain-sequence enables a PCE to select the next PCE to forward the
   path computation request based on the domain information.

   A PCC or PCE MAY add an additional constraints covering which
   Boundary Nodes (ABR or ASBR) or Border links (Inter-AS-link) MUST be
   traversed while defining a Domain-Sequence.

   Thus a Domain-Sequence MAY be made up of one or more of -

   o  AS Number

   o  Area ID

   o  Boundary Node ID

   o  Inter-AS-Link Address

   Consequently, a Domain-Sequence can be used:

   1.  by a PCE in order to discover or select the next PCE in a
       collaborative path computation, such as in BRPC [RFC5441];

   2.  by the Parent PCE to return the Domain-Sequence when unknown,
       this can further be an input to BRPC procedure [RFC6805];

   3.  by a PCC (or PCE) to constraint the domains used in a H-PCE path
       computation, explicitly specifying which domains to be expanded;

   4.  by a PCE in per-domain path computation model [RFC5152] to
       identify the next domain(s);

3.3.  Standard Representation

   Domain-Sequence MAY appear in PCEP Messages, notably in -

   o  Include Route Object (IRO): As per [RFC5440], used to specify set
      of network elements that MUST be traversed.  These subobjects are
      used to specify the domain-sequence that MUST be traversed to
      reach the destination.




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   o  Exclude Route Object (XRO): As per [RFC5521], used to specify
      certain abstract nodes that MUST be excluded from whole path.
      These subobjects are used to specify certain domains that MUST be
      avoided to reach the destination.

   o  Explicit Exclusion Route Subobject (EXRS): As per [RFC5521], used
      to specify exclusion of certain abstract nodes between a specific
      pair of nodes.  EXRS are a subobject inside the IRO.  These
      subobjects are used to specify the domains that must be excluded
      between two abstract nodes.

   o  Explicit Route Object (ERO): As per [RFC5440], used to specify a
      computed path in the network.  For example, in the case of H-PCE
      [RFC6805] Parent PCE MAY send the Domain-Sequence as a result in a
      path computation reply using ERO.

3.4.  Include Route Object (IRO)

   As per [RFC5440], IRO (Include Route Object) can be used to specify
   that the computed path MUST traverse a set of specified network
   elements or abstract nodes.

3.4.1.  Subobjects

   Some subobjects are defined in [RFC3209], [RFC3473], [RFC3477] and
   [RFC4874], but new subobjects related to Domain-Sequence are needed.

   The following subobject types are used in IRO.

                Type   Subobject
                 1     IPv4 prefix
                 2     IPv6 prefix
                 4     Unnumbered Interface ID
                 32    Autonomous system number (2 Byte)
                 33    Explicit Exclusion (EXRS)

   This document extends the above list to support 4-Byte AS numbers and
   IGP Areas.

                Type   Subobject
                 TBD   Autonomous system number (4 Byte)
                 TBD   OSPF Area id
                 TBD   ISIS Area id

   - Autonomous system

   [RFC3209] already defines 2 byte AS number.




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   To support 4 byte AS number as per [RFC4893] following subobject is
   defined:

        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    |         Reserved              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                          AS-ID (4 bytes)                      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   L: The L bit is an attribute of the subobject as defined in
      [RFC3209].

   Type:  (TBA by IANA) indicating a 4-Byte AS Number.

   Length:  8 (Total length of the subobject in bytes).

   Reserved:  Zero at transmission, ignored at receipt.

   AS-ID:  The 4-Byte AS Number.  Note that if 2-Byte AS numbers are in
      use, the low order bits (16 through 31) should be used and the
      high order bits (0 through 15) should be set to zero.

   - IGP Area

   Since the length and format of Area-id is different for OSPF and
   ISIS, following two subobjects are defined:

   For OSPF, the area-id is a 32 bit number.  The subobject is encoded
   as follows:

        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    |         Reserved              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                    OSPF Area Id (4 bytes)                     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   L: The L bit is an attribute of the subobject as defined in
      [RFC3209].

   Type:  (TBA by IANA) indicating a 4-Byte OSPF Area ID.

   Length:  8 (Total length of the subobject in bytes).




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   Reserved:  Zero at transmission, ignored at receipt.

   OSPF Area Id:  The 4-Byte OSPF Area ID.

   For IS-IS, the area-id is of variable length and thus the length of
   the Subobject is variable.  The Area-id is as described in IS-IS by
   ISO standard [ISO10589].  The subobject is encoded as follows:

        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-Len     |  Reserved     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       //                        IS-IS Area ID                        //
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   L: The L bit is an attribute of the subobject as defined in
      [RFC3209].

   Type:  (TBA by IANA) indicating IS-IS Area ID.

   Length:  Variable.  As per [RFC3209], the total length of the
      subobject in bytes, including the L, Type and Length fields.  The
      Length MUST be at least 4, and MUST be a multiple of 4.

   Area-Len:  Variable (Length of the actual (non-padded) IS-IS Area
      Identifier in octets; Valid values are from 2 to 11 inclusive).

   Reserved:  Zero at transmission, ignored at receipt.

   IS-IS Area Id:  The variable-length IS-IS area identifier.  Padded
      with trailing zeroes to a four-byte boundary.

3.4.2.  Option (A): New IRO Object Type

   [RFC5440] in its description of IRO does not require the subobjects
   to be in a given particular order.  When considering a Domain-
   Sequence, the domain relative ordering is a basic criterion and, as
   such, this option suggest a new IRO object type.










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      IRO Object-Class is 10.
      IRO Object-Type is TBD. (2 suggested value to IANA)


       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)                          //
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Subobjects: The IRO is made of subobjects identical to the ones
   defined in [RFC3209], [RFC3473], and [RFC3477], where the IRO
   subobject type is identical to the subobject type defined in the
   related documents.  Some new subobjects related to Domain-Sequence
   are also added in this document as mentioned in Section 3.4.

   [RFC3209] defines subobjects for IPv4, IPv6 and unnumbered Interface
   ID, which in the context of domain-sequence is used to specify
   Boundary Node (ABR/ASBR) and Inter-AS-Links.  The subobjects for AS
   Number (2 or 4 Byte) and IGP Area is used to specify the domain
   identifiers in the domain-sequence.

   The new IRO Object-Type used to define the domain-sequence would
   handle the L bit (Loose / Strict) in the subobjects similar to
   [RFC3209].

   Further we have following options:

   * Option (A.1):  New IRO Object Type for Domain-Sequence object only.
      A new IRO Object Type is used to specify the ordered sequence of
      domains (Domain-Sequence) only.  The PCReq message is modified to
      allow encoding of both types of IRO; one with IRO Type 1 [RFC5440]
      used to specify the intra-domain abstract nodes and resources and
      the second IRO Type with the new subobjects as described in this
      section to specify the domain-sequence.  All other rules of PCEP
      objects and message processing (ex.  P bit handling of Common
      Object Header) is as per [RFC5440].

   * Option (A.2):  New IRO Object Type for both intra and inter-domain
      (domain-sequence).  A new IRO Object Type is used to include both
      intra nodes and inter-domains nodes but the sequence of domain is
      strict.  The intra-domain nodes can still be ordered.  In case of
      inter-domain path computation, only the new IRO type is used which
      contains the specific intra domain network nodes as well as inter-
      domain abstract nodes or domains.  The inter-domain abstract nodes
      are encoded in the sequence they must be traversed but the intra-



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      domain elements MAY be an unordered set.  There is no need to
      change the PCReq message format.

3.4.2.1.  Handling of the Domain-Sequence IRO object

   An IRO object containing Domain-Sequence subobjects constraints or
   defines the domains involved in a multi-domain path computation,
   typically involving two or more collaborative PCEs.

   A Domain-Sequence can have varying degrees of granularity; it is
   possible to have a Domain-Sequence composed of, uniquely, AS
   identifiers.  It is also possible to list the involved areas for a
   given AS.

   In any case, the mapping between domains and responsible PCEs is not
   defined in this document.  It is assumed that a PCE that needs to
   obtain a "next PCE" from a Domain-Sequence is able to do so (e.g. via
   administrative configuration, or discovery).

   A PCC builds a Domain-Sequence IRO to encode the Domain-Sequence,
   that is all domains that it wishes the cooperating PCEs to traverse
   in order to compute the end to end path.

   For each inclusion, the PCC clears the L-bit to indicate that the PCE
   is required to include the domain, or sets the L-bit to indicate that
   the PCC simply desires that the domain be included in the domain-
   sequence.

   When a PCE receives a PCEP Request message with an IRO, it looks for
   a Domain-Sequence IRO (new type) to see if a domain-sequence is
   specified.  If the message contains more than one Domain-Sequence IRO
   (new type), it MUST use the first one in the message and MUST ignore
   subsequent instances.

   If a PCE does not recognize the Domain-Sequence IRO (new type), it
   MUST return a PCErr message with Error-Type "Unknown Object" and
   Error-value "Unrecognized object Type" as described in [RFC5440].

   If a PCE is unwilling or unable to process the Domain-Sequence IRO
   (new type), it MUST return a PCErr message with the Error-Type "Not
   supported object" and follow the relevant procedures described in
   [RFC5440].

   If a PCE that supports the Domain-Sequence IRO (new type) and
   encounters a subobject that it does not support or recognize, it MUST
   act according to the setting of the L-bit in the subobject.  If the
   L-bit is clear, the PCE MUST respond with a PCErr with Error-Type
   "Unrecognized subobject" and set the Error-Value to the subobject



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   type code.  If the L-bit is set, the PCE MAY respond with a PCErr as
   already stated or MAY ignore the subobject: this choice is a local
   policy decision.

   If a PCE parses a Domain-Sequence IRO (new type), it MUST act
   according to the requirements expressed in the subobject.  That is,
   if the L-bit is clear, the PCE(s) MUST produce a path that follows
   domain-sequence nodes in order identified by the subobjects in the
   path.  If the L-bit is set, the PCE(s) SHOULD produce a path along
   the Domain-Sequence unless it is not possible to construct a path
   complying with the other constraints expressed in the request.

   A successful path computation reported in a PCEP response message
   MUST include an ERO to specify the path that has been computed as
   specified in [RFC5440] following the sequence of domains.

   In a PCEP response message, PCE MAY also supply a Domain-Sequence IRO
   (new type) with the NO-PATH object indicating that the set of
   elements of the request's Domain-Sequence IRO prevented the PCE from
   finding a path.

   Subobject types for AS and IGP Area affect the next domain selection
   as well as finding the PCE serving that domain.

   Note that a particular domain in the domain-sequence can be
   identified by :-

   o  A single IGP Area: Only the IGP (OSPF or ISIS) Area subobject is
      used to identify the next domain.  (Refer Figure 1)

   o  A single AS: Only the AS subobject is used to identify the next
      domain.  (Refer Figure 2)

   o  Both an AS and an IGP Area: Combination of both AS and Area are
      used to identify the next domain.  In this case the order is AS
      Subobject followed by Area.  (Refer Figure 3)

   Subobject representing Boundary Node or Inter-AS-Link MUST be applied
   during the final path computation procedure as before.

3.4.3.  Option B: Existing IRO Object Type

   The IRO (Include Route Object) [RFC5440] is an optional object used
   to specify a set of network elements that the computed path MUST
   traverse.






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   The new subobjects denoting the domain-sequence are carried in the
   same IRO Type 1, and all the rules of processing as specified in
   [RFC5440] are applied.

   Note the following differences :-

   o  Order: Since there is no inherent order specified in the encoding
      of the subobjects in IRO Type 1 [RFC5440], it is the job of the
      PCE to figure out the optimal order of the domains to be crossed
      to reach the destination domain.  Note that in case of doubt, or
      when applicable, the PCE can still apply the ordering as specified
      in the request message.  Further PCE may have to crankback and try
      multiple permutations before figuring out the correct sequence.

   o  Loose / Strict (L-Bit): [RFC5440] state that the L bit of the
      subobjects within an IRO Type 1 [RFC5440] has no meaning.  This
      will be applicable for subobjects denoting domain-sequence as
      well.

   o  Scope: Coexistence of intra-domain nodes, boundary nodes and
      domain nodes in the same IRO List.  It is the job of PCE to figure
      out the scope and apply the processing rules accordingly.  The
      nodes in the IRO which are recognized by the PCE are handled
      locally and others are forwarded to next PCE hoping they would
      handle them, the aggregating PCE (Ingress PCE or Parent) would
      make sure that all nodes in IRO are handled correctly.

3.4.4.  Comparison

+-------------+-------------------+-------------------+-------------------+
|             |Option (A.1): New  |Option (A.2): New  |Option B: Existing |
|             |IRO Object Type for|IRO Object Type for|IRO Object Type    |
|             |Domain-Sequence    |both intra and     |                   |
|             |object only        |inter-domain       |                   |
+-------------+-------------------+-------------------+-------------------+
|Order        |Yes                |Yes                |No                 |
+-------------+-------------------+-------------------+-------------------+
|L/X bit      |Yes                |Yes                |No                 |
+-------------+-------------------+-------------------+-------------------+
|Msg Format   |No                 |Yes                |Yes                |
|Unchanged    |                   |                   |                   |
+-------------+-------------------+-------------------+-------------------+
|Seperation   |Yes                |Yes*               |No                 |
|of scope     |                   |                   |                   |
+-------------+-------------------+-------------------+-------------------+

* becasue of the ordered nature, intra-domain nodes would be first in the
  new IRO type



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   [Editor's Note: Based on our opinion and the feedback received so
   far, we feel the option A.2 should be selected.]

3.5.  Exclude Route Object (XRO)

   The Exclude Route Object (XRO) [RFC5521] is an optional object used
   to specify exclusion of certain abstract nodes or resources from the
   whole path.

3.5.1.  Subobjects

   The following subobject types are defined to be used in XRO as
   defined in [RFC3209], [RFC3477], [RFC4874], and [RFC5521].


                Type   Subobject
                 1     IPv4 prefix
                 2     IPv6 prefix
                 4     Unnumbered Interface ID
                 32    Autonomous system number (2 Byte)
                 34    SRLG
                 64    IPv4 Path Key
                 65    IPv6 Path Key

   This document extends the above list to support 4-Byte AS numbers and
   IGP Areas.


                Type   Subobject
                 TBD   Autonomous system number (4 Byte)
                 TBD   OSPF Area id
                 TBD   ISIS Area id

3.5.1.1.  Autonomous system

   The new subobjects to support 4 byte AS and IGP (OSPF / ISIS) Area
   MAY also be used in the XRO to specify exclusion of certain domains
   in the path computation procedure.

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |X|    Type     |     Length    |         Reserved              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                          AS-ID (4 bytes)                      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+





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   The X-bit indicates whether the exclusion is mandatory or desired.

   0: indicates that the AS specified MUST be excluded from the path
      computed by the PCE(s).

   1: indicates that the AS specified SHOULD be avoided from the inter-
      domain path computed by the PCE(s), but MAY be included subject to
      PCE policy and the absence of a viable path that meets the other
      constraints.

   All other fields are consistent with the definition in Section 3.4.

3.5.1.2.  IGP Area

   Since the length and format of Area-id is different for OSPF and
   ISIS, following two subobjects are defined:

   For OSPF, the area-id is a 32 bit number.  The subobject is encoded
   as follows:

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |X|    Type     |     Length    |         Reserved              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                    OSPF Area Id (4 bytes)                     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The X-bit indicates whether the exclusion is mandatory or desired.

   0: indicates that the OSFF Area specified MUST be excluded from the
      path computed by the PCE(s).

   1: indicates that the OSFF Area specified SHOULD be avoided from the
      inter-domain path computed by the PCE(s), but MAY be included
      subject to PCE policy and the absence of a viable path that meets
      the other constraints.

   All other fields are consistent with the definition in Section 3.4.

   For IS-IS, the area-id is of variable length and thus the length of
   the subobject is variable.  The Area-id is as described in IS-IS by
   ISO standard [ISO10589].  The subobject is encoded as follows:








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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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |X|    Type     |     Length    |  Area-Len     |  Reserved     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       //                        IS-IS Area ID                        //
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The X-bit indicates whether the exclusion is mandatory or desired.

   0: indicates that the ISIS Area specified MUST be excluded from the
      path computed by the PCE(s).

   1: indicates that the ISIS Area specified SHOULD be avoided from the
      inter-domain path computed by the PCE(s), but MAY be included
      subject to PCE policy and the absence of a viable path that meets
      the other constraints.

   All other fields are consistent with the definition in Section 3.4.

   If a PCE that supports XRO and encounters a subobject that it does
   not support or recognize, it MUST act according to the setting of the
   X-bit in the subobject.  If the X-bit is clear, the PCE MUST respond
   with a PCErr with Error-Type "Unrecognized subobject" and set the
   Error-Value to the subobject type code.  If the X-bit is set, the PCE
   MAY respond with a PCErr as already stated or MAY ignore the
   subobject: this choice is a local policy decision.

   All the other processing rules are as per [RFC5521].

3.6.  Explicit Exclusion Route Subobject (EXRS)

   Explicit Exclusion Route Subobject (EXRS) [RFC5521] is used to
   specify exclusion of certain abstract nodes between a specific pair
   of nodes.

   The EXRS subobject may carry any of the subobjects defined for
   inclusion in the XRO, thus the new subobjects to support 4 byte AS
   and IGP (OSPF / ISIS) Area MAY also be used in the EXRS.  The
   meanings of the fields of the new XRO subobjects are unchanged when
   the subobjects are included in an EXRS, except that scope of the
   exclusion is limited to the single hop between the previous and
   subsequent elements in the IRO.

   All the processing rules are as per [RFC5521].




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3.7.  Explicit Route Object (ERO)

   The Explicit Route Object (ERO) [RFC5440] is used to specify a
   computed path in the network.  PCEP ERO subobject types correspond to
   RSVP-TE ERO subobject types as defined in [RFC3209], [RFC3473],
   [RFC3477], [RFC4873], [RFC4874], and [RFC5520].


                Type   Subobject
                 1     IPv4 prefix
                 2     IPv6 prefix
                 3     Label
                 4     Unnumbered Interface ID
                 32    Autonomous system number (2 Byte)
                 33    Explicit Exclusion (EXRS)
                 37    Protection
                 64    IPv4 Path Key
                 65    IPv6 Path Key

   This document extends the above list to support 4-Byte AS numbers and
   IGP Areas.


                Type   Subobject
                 TBD   Autonomous system number (4 Byte)
                 TBD   OSPF Area id
                 TBD   ISIS Area id

   The new subobjects to support 4 byte AS and IGP (OSPF / ISIS) Area
   MAY also be used in the ERO to specify an abstract node (a group of
   nodes whose internal topology is opaque to the ingress node of the
   LSP).  Using this concept of abstraction, an explicitly routed LSP
   can be specified as a sequence of domains.

   In case of Hierarchical PCE [RFC6805], a Parent PCE MAY be requested
   to find the domain-sequence.  Refer example in Section 4.6.

   The format of the new ERO subobjects is similar to new IRO
   subobjects, refer Section 3.4.

4.  Other Considerations

   The examples in this section are for illustration purposes only; to
   show how the new subobjects may be encoded.







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4.1.  Inter-Area Path Computation

   In an inter-area path computation where the ingress and the egress
   nodes belong to different IGP areas within the same AS, the Domain-
   Sequence MAY be represented using a ordered list of Area subobjects.
   The AS number MAY be skipped, as area information is enough to select
   the next PCE.












































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


                   Figure 1: Inter-Area Path Computation



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   AS Number is 100.

   This could be represented in the <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.

4.2.  Inter-AS Path Computation

   In inter-AS path computation, where ingress and egress belong to
   different AS, the Domain-Sequence is represented using an ordered
   list of AS subobjects.  The Domain-Sequence MAY further include
   decomposed area information in Area subobjects.

4.2.1.  Example 1

   As shown in Figure 2, where AS to be made of a single area, the area
   subobject MAY be skipped in the Domain-Sequence as AS is enough to
   uniquely identify the next domain and PCE.












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



                    Figure 2: Inter-AS Path Computation

   Both AS are made of Area 0.

   This could be represented in the <IRO> as:














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       +---------+  +---------+  +---------+
       |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 subobject is optional and it MAY be skipped.  PCE should be able
   to understand both notations.

4.2.2.  Example 2

   As shown in Figure 3, where AS 200 is made up of multiple areas and
   multiple domain-sequence exist, PCE MAY include both AS and Area
   subobject to uniquely identify the next domain and PCE.

                  |
                  |  +-------------+                +----------------+
                  |  |Area 2       |                |Area 4          |
                  |  |         +--+|                |          +--+  |
                  |  |         |  ||                |          |  |  |
                  |  |  +--+   +--+|                |   +--+   +--+  |
                  |  |  |  |       |                |   |  |         |
                  |  |  *--+       |                |   +--+         |
                  |  | /      +--+ |                |          +--+  |
                  |  |/       |  | |                |          |  |  |
                  |  /        +--+ |                |   +--+   +--+  |
                  | /|  +--+       |+--------------+|   |  |         |
                  |/ |  |  |       ++-+          +-++   +--+         |
   +-------------+/  |  +--+       || |          | ||                |
   |             /|  |             ++-+          +-++                |
   |         +--*||  +-------------+|              |+----------------+
   |         |  |||                 |     +--+     |
   |         +--+||                 |     |  |     |
   |    +--+     ||                 |     +--+     |
   |    |  |     ||                 |              |
   |    +--+     ||                 |              |



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   |             ||                 |     +--+     |
   |+--+         ||                 |     |  |     |
   ||  |         ||                 |     +--+     |
   |+--+         ||                 |              |
   |             ||                 |     +--+     |
   |    +--+     ||  +------------+ |     |  |     |+----------------+
   |    |  |     ||  |Area 3      +-++    +--+   +-++ Area 5         |
   |    +--+     ||  |            | ||           | ||                |
   |             ||  |            +-++           +-++                |
   |         +--+||  |       +--+ | |  Area 0      ||   +--+         |
   |         |  |||  |       |  | | +--------------+|   |  |         |
   |         +--*||  |       +--+ |                 |   +--+         |
   |             \|  |            |                 |          +--+  |
   |Area 1       |\  |   +--+     |                 |   +--+   |  |  |
   +-------------+|\ |   |  |     |                 |   |  |   +--+  |
                  | \|   +--+  +--+                 |   +--+         |
                  |  \         |  |                 |                |
                  |  |\        +--+                 |          +--+  |
                  |  | \ +--+     |                 |          |  |  |
                  |  |  \|  |     |                 |          +--+  |
                  |  |   *--+     |                 |                |
                  |  |            |                 |                |
                  |  +------------+                 +----------------+
                  |
                  |
       AS 100     |  AS 200
                  |

                    Figure 3: Inter-AS Path Computation

   The Domain-Sequence can be carried in the 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 |
   |       | |       | |       | |       | |       | |       | |       |
   +-------+ +-------+ +-------+ +-------+ +-------+ +-------+ +-------+

   The combination of both an AS and an Area uniquely identify a domain
   in the Domain-Sequence.

   Note that an Area domain identifier always belongs to the previous AS
   that appears before it or, if no AS subobjects are present, it is
   assumed to be the current AS.





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   If the area information cannot be provided, PCE MAY forward the path
   computation request to the next PCE based on AS alone.  If multiple
   PCEs are responsible, PCE MAY apply local policy to select the next
   PCE.

4.3.  Boundary Node and Inter-AS-Link

   A PCC or PCE MAY add additional constraints covering which Boundary
   Nodes (ABR or ASBR) or Border links (Inter-AS-link) MUST be traversed
   while defining a Domain-Sequence.  In which case the Boundary Node or
   Link MAY be encoded as a part of the domain-sequence using the
   existing subobjects.

   Boundary Nodes (ABR / ASBR) can be encoded using the IPv4 or IPv6
   prefix subobjects usually the loopback address of 32 and 128 prefix
   length respectively.  An Inter-AS link can be encoded using the IPv4
   or IPv6 prefix subobjects or unnumbered interface subobjects.

   For Figure 1, an ABR to be traversed can be specified as:


        +---------+ +---------+ +---------++---------+ +---------+
        |IRO      | |Sub      | |Sub      ||Sub      | |Sub      |
        |Object   | |Object   | |Object   ||Object   | |Object   |
        |Header   | |Area 2   | |IPv4     ||Area 0   | |Area 4   |
        |         | |         | |x.x.x.x  ||         | |         |
        |         | |         | |         ||         | |         |
        +---------+ +---------+ +---------++---------+ +---------+


   For Figure 2, an inter-AS-link to be traversed can be specified as:

          +---------+  +---------+ +---------+ +---------+ +---------+
          |IRO      |  |Sub      | |Sub      | |Sub      | |Sub      |
          |Object   |  |Object AS| |Object   | |Object   | |Object AS|
          |Header   |  |100      | |IPv4     | |IPv4     | |200      |
          |         |  |         | |x.x.x.x  | |x.x.x.x  | |         |
          |         |  |         | |         | |         | |         |
          +---------+  +---------+ +---------+ +---------+ +---------+

4.4.  PCE Serving multiple Domains

   A single PCE MAY be responsible for multiple domains; for example PCE
   function deployed on an ABR.  A PCE which can support 2 adjacent
   domains can internally handle this situation without any impact on
   the neighboring domains.





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4.5.  P2MP

   In case of inter-domain P2MP path computation, (Refer
   [PCE-P2MP-PROCEDURES]) the path domain tree is nothing but a series
   of Domain Sequences, as shown in the below figure:

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

   All rules of processing as applied to P2P can be applied to P2MP as
   well.

   In case of P2MP, different destinations MAY have different Domain-
   Sequence within the domain tree, it requires domain-sequence to be
   attached per destination.  (Refer [PCE-P2MP-PER-DEST])

4.6.  Hierarchical PCE

   As per [RFC6805], consider a case as shown in Figure 4 consisting of
   multiple child PCEs and a parent PCE.



























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

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

                        Figure 4: Hierarchical PCE





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   In H-PCE, the Ingress PCE PCE(1) can request the parent PCE to
   determine the Domain-Sequence and return it in the PCEP response,
   using the ERO Object.  The ERO can contain an ordered sequence of
   subobjects such as AS and Area (OSPF/ISIS) subobjects.  In this case,
   the Domain-Sequence appear 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   |
     |         | |         | |         | |         | |         |
     |         | |         | |         | |         | |         |
     +---------+ +---------+ +---------+ +---------+ +---------+

   Note that, in the case of ERO objects, no new PCEP object type is
   required since the ordering constraint is assumed.

4.7.  Relationship to PCE Sequence

   Instead of a domain-sequence, a sequence of PCEs MAY be enforced by
   policy on the PCC, and this constraint can be carried in the PCReq
   message (as defined in [RFC5886]).

   Note that PCE-Sequence can be used along with domain-sequence in
   which case PCE-Sequence SHOULD have higher precedence in selecting
   the next PCE in the inter-domain path computation procedures.  Note
   that Domain-Sequence IRO constraints should still be checked as per
   the rules of processing IRO.

4.8.  Relationship to RSVP-TE

   [RFC3209] already describes the notion of abstract nodes, where an
   abstract node is a group of nodes whose internal topology is opaque
   to the ingress node of the LSP.  It further defines a subobject for
   AS but with a 2-Byte AS Number.

   [DOMAIN-SUBOBJ] extends the notion of abstract nodes by adding new
   subobjects for IGP Areas and 4-byte AS numbers.  These subobjects MAY



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   be included in Explicit Route Object (ERO), Exclude Route object
   (XRO) or Explicit Exclusion Route Subobject (EXRS) in RSVP-TE.

   In any case subobject type defined in RSVP-TE are identical to the
   subobject type defined in the related documents in PCEP.

5.  IANA Considerations

5.1.  PCEP Objects

   The "PCEP Parameters" registry contains a subregistry "PCEP Objects".
   IANA is requested to make the following allocations from this
   registry.

       Object        Name                     Reference
       Class
       10            IRO                      [RFC5440]
                      Object-Type
                       (TBA): Domain-Sequence [This I.D.]

5.2.  New Subobjects

   The "PCEP Parameters" registry contains a subregistry "PCEP Objects"
   with an entry for the Include Route Object (IRO), Exclude Route
   Object (XRO) and Explicit Route Object (ERO).  IANA is requested to
   add further subobjects as follows:

       7  ERO
       10 IRO
       17 XRO

       Subobject Type                          Reference
       TBA       4 byte AS number              [This I.D.]
       TBA       OSPF Area ID                  [This I.D.]
       TBA       IS-IS Area ID                 [This I.D.]

5.3.  Error Object Field Values

   The "PCEP Parameters" registry contains a subregistry "Error Types
   and Values".  IANA is requested to make the following allocations
   from this subregistry

       ERROR     Meaning                       Reference
       Type
       TBA       "Unrecognized subobject"      [This I.D.]
                 Error-Value: type code





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6.  Security Considerations

   This document specifies a standard representation of Domain-Sequence
   and new subobjects, which MAY be used in inter-domain PCE scenarios
   as explained in other RFC and drafts.  The new subobjects and Domain-
   Sequence mechanisms defined in this document allow finer and more
   specific control of the path computed by a cooperating PCE(s).  Such
   control increases the risk if a PCEP message is intercepted,
   modified, or spoofed because it allows the attacker to exert control
   over the path that the PCE will compute or to make the path
   computation impossible.  Therefore, the security techniques described
   in [RFC5440] are considered more important.

   Note, however, that the Domain-Sequence mechanisms also provide the
   operator with the ability to route around vulnerable parts of the
   network and may be used to increase overall network security.

7.  Manageability Considerations

7.1.  Control of Function and Policy

   Several local policy decisions should be made at the PCE.  Firstly,
   the exact behavior with regard to desired inclusion and exclusion of
   domains must be available for examination by an operator and may be
   configurable.  Second, the behavior on receipt of an unrecognized
   subobjects with the L or X-bit set should be configurable and must be
   available for inspection.  The inspection and control of these local
   policy choices may be part of the PCEP MIB module.

7.2.  Information and Data Models

   A MIB module for management of the PCEP is being specified in a
   separate document [PCEP-MIB].  That MIB module allows examination of
   individual PCEP messages, in particular requests, responses and
   errors.  The MIB module MUST be extended to include the ability to
   view the domain-sequence extensions defined in this document.

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 [RFC5440].

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
   [RFC5440].



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7.5.  Requirements On Other Protocols

   In case of per-domain path computation [RFC5152], where the full path
   of an inter-domain TE LSP cannot be or is not determined at the
   ingress node, and signaling message may use domain identifiers.  The
   Subobjects defined in this document SHOULD be supported by RSVP-TE.
   [DOMAIN-SUBOBJ] extends the notion of abstract nodes by adding new
   subobjects for IGP Areas and 4-byte AS numbers.

   Apart from this, mechanisms defined in this document do not imply any
   requirements on other protocols in addition to those already listed
   in [RFC5440].

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 [RFC5440].

8.  Acknowledgments

   We would like to thank Adrian Farrel, Pradeep Shastry, Suresh Babu,
   Quintin Zhao, Fatai Zhang, Daniel King, Oscar Gonzalez, Chen Huaimo,
   Venugopal Reddy, Reeja Paul Sandeep Boina and Avantika 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

   [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.

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

   [RFC3477]  Kompella, K. and Y. Rekhter, "Signalling Unnumbered Links
              in Resource ReSerVation Protocol - Traffic Engineering
              (RSVP-TE)", RFC 3477, January 2003.

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



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   [RFC4726]  Farrel, A., Vasseur, J., and A. Ayyangar, "A Framework for
              Inter-Domain Multiprotocol Label Switching Traffic
              Engineering", RFC 4726, November 2006.

   [RFC4873]  Berger, L., Bryskin, I., Papadimitriou, D., and A. Farrel,
              "GMPLS Segment Recovery", RFC 4873, May 2007.

   [RFC4874]  Lee, CY., Farrel, A., and S. De Cnodder, "Exclude Routes -
              Extension to Resource ReserVation Protocol-Traffic
              Engineering (RSVP-TE)", RFC 4874, April 2007.

   [RFC4893]  Vohra, Q. and E. Chen, "BGP Support for Four-octet AS
              Number Space", RFC 4893, May 2007.

   [RFC5152]  Vasseur, JP., Ayyangar, A., and R. Zhang, "A Per-Domain
              Path Computation Method for Establishing Inter-Domain
              Traffic Engineering (TE) Label Switched Paths (LSPs)", RFC
              5152, February 2008.

   [RFC5440]  Vasseur, JP. and JL. Le Roux, "Path Computation Element
              (PCE) Communication Protocol (PCEP)", RFC 5440, 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", RFC 5441, April 2009.

   [RFC5520]  Bradford, R., Vasseur, JP., and A. Farrel, "Preserving
              Topology Confidentiality in Inter-Domain Path Computation
              Using a Path-Key-Based Mechanism", RFC 5520, April 2009.

   [RFC5521]  Oki, E., Takeda, T., and A. Farrel, "Extensions to the
              Path Computation Element Communication Protocol (PCEP) for
              Route Exclusions", RFC 5521, April 2009.

   [RFC5886]  Vasseur, JP., Le Roux, JL., and Y. Ikejiri, "A Set of
              Monitoring Tools for Path Computation Element (PCE)-Based
              Architecture", RFC 5886, June 2010.

   [RFC6805]  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", RFC 6805, November
              2012.







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   [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)", July 2013.

   [PCEP-MIB]
              Koushik, A., Emile, S., Zhao, Q., King, D., and J.
              Hardwick, "PCE communication protocol(PCEP) Management
              Information Base", July 2013.

   [PCE-P2MP-PER-DEST]
              Dhody, D., Palle, U., and V. Kondreddy, "Supporting
              explicit inclusion or exclusion of abstract nodes for a
              subset of P2MP destinations in Path Computation Element
              Communication Protocol (PCEP). (draft-dhody-pce-pcep-p2mp-
              per-destination)", October 2013.

   [DOMAIN-SUBOBJ]
              Dhody, D., Palle, U., Kondreddy, V., and R. Casellas,
              "Domain Subobjects for Resource ReserVation Protocol -
              Traffic Engineering (RSVP-TE). (draft-dhody-ccamp-rsvp-te-
              domain-subobjects)", January 2014.

   [ISO10589]
              ISO, "Intermediate system to Intermediate system routing
              information exchange protocol for use in conjunction with
              the Protocol for providing the Connectionless-mode Network
              Service (ISO 8473)", ISO/IEC 10589:2002, 1992.

Authors' Addresses

   Dhruv Dhody
   Huawei Technologies
   Leela Palace
   Bangalore, Karnataka  560008
   INDIA

   EMail: dhruv.ietf@gmail.com











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   Udayasree Palle
   Huawei Technologies
   Leela Palace
   Bangalore, Karnataka  560008
   INDIA

   EMail: udayasree.palle@huawei.com


   Ramon Casellas
   CTTC
   Av. Carl Friedrich Gauss n7
   Castelldefels, Barcelona    08860
   SPAIN

   EMail: ramon.casellas@cttc.es



































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