GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc7897

Internet Engineering Task Force (IETF) D. Dhody Request for Comments: 7897 U. Palle Category: Experimental Huawei Technologies ISSN: 2070-1721 R. Casellas

                                                                  CTTC
                                                             June 2016
                         Domain Subobjects
   for the Path Computation Element Communication Protocol (PCEP)

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 System (AS).  This
 document specifies a 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 constrained
 shortest 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 document is not an Internet Standards Track specification; it is
 published for examination, experimental implementation, and
 evaluation.
 This document defines an Experimental Protocol for the Internet
 community.  This document is a product of the Internet Engineering
 Task Force (IETF).  It represents the consensus of the IETF
 community.  It has received public review and has been approved for
 publication by the Internet Engineering Steering Group (IESG).  Not
 all documents approved by the IESG are a candidate for any level of
 Internet Standard; see Section 2 of RFC 7841.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc7897.

Dhody, et al. Experimental [Page 1] RFC 7897 Domain Subobjects for PCEP June 2016

Copyright Notice

 Copyright (c) 2016 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.  Scope . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   1.2.  Requirements Language . . . . . . . . . . . . . . . . . .   4
 2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
 3.  Detail Description  . . . . . . . . . . . . . . . . . . . . .   6
   3.1.  Domains . . . . . . . . . . . . . . . . . . . . . . . . .   6
   3.2.  Domain Sequence . . . . . . . . . . . . . . . . . . . . .   6
   3.3.  Domain Sequence Representation  . . . . . . . . . . . . .   7
   3.4.  Include Route Object (IRO)  . . . . . . . . . . . . . . .   8
     3.4.1.  Subobjects  . . . . . . . . . . . . . . . . . . . . .   8
       3.4.1.1.  Autonomous System . . . . . . . . . . . . . . . .   8
       3.4.1.2.  IGP Area  . . . . . . . . . . . . . . . . . . . .   9
     3.4.2.  Update in IRO Specification . . . . . . . . . . . . .  10
     3.4.3.  IRO for Domain Sequence . . . . . . . . . . . . . . .  11
       3.4.3.1.  PCC Procedures  . . . . . . . . . . . . . . . . .  11
       3.4.3.2.  PCE Procedures  . . . . . . . . . . . . . . . . .  11
   3.5.  Exclude Route Object (XRO)  . . . . . . . . . . . . . . .  13
     3.5.1.  Subobjects  . . . . . . . . . . . . . . . . . . . . .  13
       3.5.1.1.  Autonomous System . . . . . . . . . . . . . . . .  14
       3.5.1.2.  IGP Area  . . . . . . . . . . . . . . . . . . . .  14
   3.6.  Explicit Exclusion Route Subobject (EXRS) . . . . . . . .  16
   3.7.  Explicit Route Object (ERO) . . . . . . . . . . . . . . .  16
 4.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  17
   4.1.  Inter-Area Path Computation . . . . . . . . . . . . . . .  17
   4.2.  Inter-AS Path Computation . . . . . . . . . . . . . . . .  19
     4.2.1.  Example 1 . . . . . . . . . . . . . . . . . . . . . .  20
     4.2.2.  Example 2 . . . . . . . . . . . . . . . . . . . . . .  22
   4.3.  Boundary Node and Inter-AS Link . . . . . . . . . . . . .  25
   4.4.  PCE Serving Multiple Domains  . . . . . . . . . . . . . .  25
   4.5.  P2MP  . . . . . . . . . . . . . . . . . . . . . . . . . .  26
   4.6.  Hierarchical PCE  . . . . . . . . . . . . . . . . . . . .  27

Dhody, et al. Experimental [Page 2] RFC 7897 Domain Subobjects for PCEP June 2016

 5.  Other Considerations  . . . . . . . . . . . . . . . . . . . .  27
   5.1.  Relationship to PCE Sequence  . . . . . . . . . . . . . .  27
   5.2.  Relationship to RSVP-TE . . . . . . . . . . . . . . . . .  27
 6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  28
   6.1.  New Subobjects  . . . . . . . . . . . . . . . . . . . . .  28
 7.  Security Considerations . . . . . . . . . . . . . . . . . . .  28
 8.  Manageability Considerations  . . . . . . . . . . . . . . . .  29
   8.1.  Control of Function and Policy  . . . . . . . . . . . . .  29
   8.2.  Information and Data Models . . . . . . . . . . . . . . .  29
   8.3.  Liveness Detection and Monitoring . . . . . . . . . . . .  30
   8.4.  Verify Correct Operations . . . . . . . . . . . . . . . .  30
   8.5.  Requirements on Other Protocols . . . . . . . . . . . . .  30
   8.6.  Impact on Network Operations  . . . . . . . . . . . . . .  30
 9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  31
   9.1.  Normative References  . . . . . . . . . . . . . . . . . .  31
   9.2.  Informative References  . . . . . . . . . . . . . . . . .  32
 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  34
 Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  35

1. Introduction

 A Path Computation Element (PCE) may be used to compute end-to-end
 paths across multi-domain environments using a per-domain path
 computation technique [RFC5152].  The Backward-Recursive PCE-Based
 Computation (BRPC) mechanism [RFC5441] also defines a PCE-based path
 computation procedure to compute an inter-domain constrained path for
 (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 and is either fixed by the network operator or obtained by
 other means.  Also, for inter-domain point-to-multipoint (P2MP) tree
 computation, it is assumed per [RFC7334] that the domain tree is
 known a priori.
 The list of domains (domain sequence) in point-to-point (P2P) or a
 domain tree in P2MP is usually a constraint in inter-domain path
 computation procedure.
 The domain sequence (the set of domains traversed to reach the
 destination domain) is either administratively predetermined or
 discovered by some means like Hierarchical PCE (H-PCE).
 [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 an
 Autonomous System (albeit with a 2-byte AS number) as an abstract
 node representing a domain is defined in [RFC3209].  In the current
 document, we specify new subobjects to include or exclude domains
 including an IGP area or an AS (4 bytes as per [RFC6793]).

Dhody, et al. Experimental [Page 3] RFC 7897 Domain Subobjects for PCEP June 2016

 Further, the domain identifier may simply act as a delimiter to
 specify where the domain boundary starts and ends in some cases.
 This is a companion document to Resource Reservation Protocol -
 Traffic Engineering (RSVP-TE) extensions for the domain identifiers
 [RFC7898].

1.1. Scope

 The procedures described in this document are experimental.  The
 experiment is intended to enable research for the usage of the domain
 sequence at the PCEs for inter-domain paths.  For this purpose, this
 document specifies new domain subobjects as well as how they
 incorporate with existing subobjects to represent a domain sequence.
 The experiment will end two years after the RFC is published.  At
 that point, the RFC authors will attempt to determine how widely this
 has been implemented and deployed.
 This document does not change the procedures for handling existing
 subobjects in the PCE Communication Protocol (PCEP).
 The new subobjects introduced by this document will not be understood
 by legacy implementations.  If a legacy implementation receives one
 of the subobjects that it does not understand in a PCEP object, the
 legacy implementation will behave according to the rules for a
 malformed object as per [RFC5440].  Therefore, it is assumed that
 this experiment will be conducted only when both the PCE and the Path
 Computation Client (PCC) form part of the experiment.  It is possible
 that a PCC or PCE can operate with peers, some of which form part of
 the experiment and some that do not.  In this case, since no
 capabilities exchange is used to identify which nodes can use these
 extensions, manual configuration should be used to determine which
 peerings form part of the experiment.
 When the results of implementation and deployment are available, this
 document will be updated and refined, and then it could be moved from
 Experimental to Standards Track.

1.2. 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].

Dhody, et al. Experimental [Page 4] RFC 7897 Domain Subobjects for PCEP June 2016

2. Terminology

 The following terminology is used in this document.
 ABR:  Area Border Router.  Routers used to connect two IGP areas
    (Open Shortest Path First (OSPF) or Intermediate System to
    Intermediate System (IS-IS).
 AS:  Autonomous System
 ASBR:  Autonomous System Border Router
 BN:  Boundary node; can be an ABR or ASBR.
 BRPC:  Backward-Recursive PCE-Based 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 IGP area and AS.
 Domain Sequence:  An ordered sequence of domains traversed to reach
    the destination domain.
 ERO:  Explicit Route Object
 H-PCE:  Hierarchical PCE
 IGP:  Interior Gateway Protocol.  Either of the two routing
    protocols: OSPF or 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

Dhody, et al. Experimental [Page 5] RFC 7897 Domain Subobjects for PCEP June 2016

 RSVP:  Resource Reservation Protocol
 TE LSP:  Traffic Engineering Label Switched Path
 XRO:  Exclude Route Object

3. Detail Description

3.1. Domains

 [RFC4726] and [RFC4655] define a domain as a separate administrative
 or geographic environment within the network.  A domain could 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 an
 area-id, AS number, 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 a
 path computation request to a PCE(s).  A domain sequence can also be
 the result of a path computation.  For example, in the case of H-PCE
 [RFC6805], a parent PCE could send the domain sequence as a result in
 a path computation reply.
 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 a list of
 domain sequences.
 A domain sequence enables a PCE to select the next domain and the PCE
 serving that domain to forward the path computation request based on
 the domain information.
 A domain sequence can include boundary nodes (ABR or ASBR) or border
 links (inter-AS links) to be traversed as an additional constraint.

Dhody, et al. Experimental [Page 6] RFC 7897 Domain Subobjects for PCEP June 2016

 Thus, a domain sequence can be made up of one or more of the
 following:
 o  AS Number
 o  Area ID
 o  Boundary Node ID
 o  Inter-AS Link Address
 These are encoded in the new subobjects defined in this document as
 well as in the existing subobjects that represent a domain sequence.
 Consequently, a domain sequence can be used by:
 1.  a PCE in order to discover or select the next PCE in a
     collaborative path computation, such as in BRPC [RFC5441];
 2.  the parent PCE to return the domain sequence when unknown; this
     can then be an input to the BRPC procedure [RFC6805];
 3.  a PCC or a PCE to constrain the domains used in inter-domain path
     computation, explicitly specifying which domains to be expanded
     or excluded; and
 4.  a PCE in the per-domain path computation model [RFC5152] to
     identify the next domain.

3.3. Domain Sequence Representation

 A domain sequence appears in PCEP messages, notably in:
 o  Include Route Object (IRO): As per [RFC5440], IRO can be used to
    specify a set of network elements to be traversed to reach the
    destination, which includes subobjects used to specify the domain
    sequence.
 o  Exclude Route Object (XRO): As per [RFC5521], XRO can be used to
    specify certain abstract nodes, to be excluded from the whole
    path, which include subobjects used to specify the domain
    sequence.
 o  Explicit Exclusion Route Subobject (EXRS): As per [RFC5521], EXRS
    can be used to specify exclusion of certain abstract nodes
    (including domains) between a specific pair of nodes.  EXRS is a
    subobject inside the IRO.

Dhody, et al. Experimental [Page 7] RFC 7897 Domain Subobjects for PCEP June 2016

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

3.4. Include Route Object (IRO)

 As per [RFC5440], IRO can be used to specify that the computed path
 needs to 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.
 This document extends the support for 4-byte AS numbers and IGP
 areas.
               Value  Description
               -----  ----------------
               5      4-byte AS number
               6      OSPF Area ID
               7      IS-IS Area ID
 Note: Identical subobjects are carried in RSVP-TE messages as defined
 in [RFC7898].

3.4.1.1. Autonomous System

 [RFC3209] already defines 2-byte AS numbers.
 To support 4-byte AS numbers as per [RFC6793], the 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 Number (4 bytes)                      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 L: The L bit is an attribute of the subobject as defined in
    [RFC3209], and its usage in the IRO subobject is defined in
    [RFC7896].
 Type:  5 (indicating a 4-byte AS number).

Dhody, et al. Experimental [Page 8] RFC 7897 Domain Subobjects for PCEP June 2016

 Length:  8 (total length of the subobject in bytes).
 Reserved:  Zero at transmission; ignored at receipt.
 AS Number:  The 4-byte AS number.  Note that if 2-byte AS numbers are
    in use, the low-order bits (16 through 31) MUST be used, and the
    high-order bits (0 through 15) MUST be set to zero.

3.4.1.2. IGP Area

 Since the length and format of Area ID is different for OSPF and
 IS-IS, the following two subobjects are defined below:
 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], and its usage in the IRO subobject is defined in
    [RFC7896].
 Type:  6 (indicating a 4-byte OSPF Area ID).
 Length:  8 (total length of the subobject in bytes).
 Reserved:  Zero at transmission; ignored at receipt.
 OSPF Area ID:  The 4-byte OSPF Area ID.

Dhody, et al. Experimental [Page 9] RFC 7897 Domain Subobjects for PCEP June 2016

 For IS-IS, the Area ID is of variable length; thus, the length of the
 subobject is variable.  The Area ID is as described in IS-IS by the
 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], and its usage in the IRO subobject is defined in
    [RFC7896].
 Type:  7 (indicating the IS-IS Area ID).
 Length:  Variable.  The length MUST be at least 8 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 1 to 13, 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 4-byte boundary.

3.4.2. Update in IRO Specification

 [RFC5440] describes IRO as an optional object used to specify network
 elements to be traversed by the computed path.  It further states
 that the L bit of such subobject has no meaning within an IRO.  It
 also does not mention if IRO is an ordered or unordered list of
 subobjects.
 An update to the IRO specification [RFC7896] makes IRO as an ordered
 list and includes support for the L bit.
 The use of IRO for the domain sequence assumes the updated
 specification is being used for IRO, as per [RFC7896].

Dhody, et al. Experimental [Page 10] RFC 7897 Domain Subobjects for PCEP June 2016

3.4.3. IRO for Domain Sequence

 The subobject type for IPv4, IPv6, and unnumbered Interface IDs can
 be used to specify boundary nodes (ABR/ASBR) and inter-AS links.  The
 subobject type for the AS Number (2 or 4 bytes) and the IGP area are
 used to specify the domain identifiers in the domain sequence.
 The IRO can incorporate the new domain subobjects with the existing
 subobjects in a sequence of traversal.
 Thus, an IRO, comprising subobjects, that represents a domain
 sequence defines the domains involved in an inter-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 IGP 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).

3.4.3.1. PCC Procedures

 A PCC builds an IRO to encode the domain sequence, so that the
 cooperating PCEs could compute an inter-domain shortest constrained
 path across the specified sequence of domains.
 A PCC may intersperse area and AS subobjects with other subobjects
 without change to the previously specified processing of those
 subobjects in the IRO.

3.4.3.2. PCE Procedures

 If a PCE receives an IRO in a Path Computation Request (PCReq)
 message that contains the subobjects defined in this document that it
 does not recognize, it will respond according to the rules for a
 malformed object as per [RFC5440].  The PCE MAY also include the IRO
 in the PCEP Error (PCErr) message as per [RFC5440].
 The interpretation of the L bit is as per Section 4.3.3.1 of
 [RFC3209] (as per [RFC7896]).

Dhody, et al. Experimental [Page 11] RFC 7897 Domain Subobjects for PCEP June 2016

 In a Path Computation Reply (PCRep), PCE MAY also supply IRO (with
 domain sequence information) with the NO-PATH object indicating that
 the set of elements (domains) of the request's IRO prevented the PCEs
 from finding a path.
 The following processing rules apply for a domain sequence in IRO:
 o  When a PCE parses an IRO, it interprets each subobject according
    to the AS number associated with the preceding subobject.  We call
    this the "current AS".  Certain subobjects modify the current AS,
    as follows.
  • The current AS is initialized to the AS number of the PCC.
  • If the PCE encounters an AS subobject, then it updates the

current AS to this new AS number.

  • If the PCE encounters an area subobject, then it assumes that

the area belongs to the current AS.

  • If the PCE encounters an IP address that is globally routable,

then it updates the current AS to the AS that owns this IP

       address.  This document does not define how the PCE learns
       which AS owns the IP address.
  • If the PCE encounters an IP address that is not globally

routable, then it assumes that it belongs to the current AS.

  • If the PCE encounters an unnumbered link, then it assumes that

it belongs to the current AS.

 o  When a PCE parses an IRO, it interprets each subobject according
    to the Area ID associated with the preceding subobject.  We call
    this the "current area".  Certain subobjects modify the current
    area, as follows.
  • The current area is initialized to the Area ID of the PCC.
  • If the current AS is changed, the current area is reset and

needs to be determined again by a current or subsequent

       subobject.
  • If the PCE encounters an area subobject, then it updates the

current area to this new Area ID.

Dhody, et al. Experimental [Page 12] RFC 7897 Domain Subobjects for PCEP June 2016

  • If the PCE encounters an IP address that belongs to a different

area, then it updates the current area to the area that has

       this IP address.  This document does not define how the PCE
       learns which area has the IP address.
  • If the PCE encounters an unnumbered link that belongs to a

different area, then it updates the current Area to the area

       that has this link.
  • Otherwise, it assumes that the subobject belongs to the current

area.

 o  In case the current PCE is not responsible for the path
    computation in the current AS or area, then the PCE selects the
    "next PCE" in the domain sequence based on the current AS and
    area.
 Note that it is advised that PCC should use AS and area subobjects
 while building the domain sequence in IRO and avoid using other
 mechanisms to change the "current AS" and "current area" as described
 above.

3.5. Exclude Route Object (XRO)

 XRO [RFC5521] is an optional object used to specify exclusion of
 certain abstract nodes or resources from the whole path.

3.5.1. Subobjects

 Some subobjects are to be used in XRO as defined in [RFC3209],
 [RFC3477], [RFC4874], and [RFC5520], but new subobjects related to
 domain sequence are needed.
 This document extends the support for 4-byte AS numbers and IGP
 areas.
               Value  Description
               -----  ----------------
               5      4-byte AS number
               6      OSPF Area ID
               7      IS-IS Area ID
 Note: Identical subobjects are carried in RSVP-TE messages as defined
 in [RFC7898].

Dhody, et al. Experimental [Page 13] RFC 7897 Domain Subobjects for PCEP June 2016

3.5.1.1. Autonomous System

 The new subobjects to support 4-byte AS numbers and the IGP
 (OSPF/IS-IS) 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 Number (4 bytes)                      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 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 it 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 the Area ID is different for OSPF and
 IS-IS, the 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 OSPF area specified MUST be excluded from the
    path computed by the PCE(s).

Dhody, et al. Experimental [Page 14] RFC 7897 Domain Subobjects for PCEP June 2016

 1: indicates that the OSPF area specified SHOULD be avoided from the
    inter-domain path computed by the PCE(s), but it 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; thus, the length of the
 subobject is variable.  The Area ID is as described in IS-IS by the
 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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |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 IS-IS area specified MUST be excluded from the
    path computed by the PCE(s).
 1: indicates that the IS-IS area specified SHOULD be avoided from the
    inter-domain path computed by the PCE(s), but it 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.
 All the processing rules are as per [RFC5521].
 Note that if a PCE receives an XRO in a PCReq message that contains
 subobjects defined in this document that it does not recognize, it
 will respond according to the rules for a malformed object as per
 [RFC5440].
 IGP area subobjects in the XRO are local to the current AS.  In case
 multi-AS path computation excludes an IGP area in a different AS, the
 IGP area subobject should be part of EXRS in the IRO to specify the
 AS in which the IGP area is to be excluded.  Further, policy may be
 applied to prune/ignore area subobjects in XRO after a "current AS"
 change during path computation.

Dhody, et al. Experimental [Page 15] RFC 7897 Domain Subobjects for PCEP June 2016

3.6. Explicit Exclusion Route Subobject (EXRS)

 The EXRS [RFC5521] is used to specify exclusion of certain abstract
 nodes between a specific pair of nodes.
 The EXRS can carry any of the subobjects defined for inclusion in the
 XRO; thus, the new subobjects to support 4-byte AS numbers and the
 IGP (OSPF / IS-IS) area can 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 the scope of the
 exclusion is limited to the single hop between the previous and
 subsequent elements in the IRO.
 The EXRS should be interpreted in the context of the current AS and
 current area of the preceding subobject in the IRO.  The EXRS does
 not change the current AS or current area.  All other processing
 rules are as per [RFC5521].
 Note that if a PCE that supports the EXRS in an IRO parses an IRO,
 and encounters an EXRS that contains subobjects defined in this
 document that it does not recognize, it will act according to the
 setting of the X-bit in the subobject as per [RFC5521].

3.7. Explicit Route Object (ERO)

 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].  The subobjects related to the domain sequence are further
 defined in [RFC7898].
 The new subobjects to support 4-byte AS numbers and the IGP
 (OSPF/IS-IS) area can 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 H-PCE [RFC6805], a parent PCE can be requested to find the
 domain sequence.  Refer to the example in Section 4.6 of this
 document.  The ERO in reply from the parent PCE can then be used in
 per-domain path computation or BRPC.
 If a PCC receives an ERO in a PCRep message that contains a subobject
 defined in this document that it does not recognize, it will respond
 according to the rules for a malformed object as per [RFC5440].

Dhody, et al. Experimental [Page 16] RFC 7897 Domain Subobjects for PCEP June 2016

4. Examples

 The examples in this section are for illustration purposes only to
 highlight how the new subobjects could be encoded.  They are not
 meant to be an exhaustive list of all possible use cases and
 combinations.

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 could be represented using an ordered list of area
 subobjects.

Dhody, et al. Experimental [Page 17] RFC 7897 Domain Subobjects for PCEP June 2016

  1. —————- —————–

| | | |

 |          +--+   |                            |     +--+        |
 | +--+     |  |   |                            |     |  |        |
 | |  |     +--+   |                            |     +--+   +--+ |
 | +--+            |                            |            |  | |
 |                 |                            |            +--+ |
 |        +--+     |                            |                 |
 |        |  |     |                            |     +--+        |
 |        +--+     |                            |     |  |        |
 |                 | -------------------------- |     +--+        |
 |                +--+                       +--+                 |
 |                |  |         +--+          |  |                 |
 |Area 2          +--+         |  |          +--+  Area 4         |
  ----------------- |          +--+            | -----------------
                    |                          |
                    |                +--+      |
                    |    +--+        |  |      |
                    |    |  |        +--+      |
                    |    +--+                  |
                    |                          |
                    |                          |
                    |                          |
                    |                          |
                    |           +--+           |
                    |           |  |           |
                    |           +--+           |
  ----------------- |                          | ------------------
 |                 +--+                      +--+                  |
 |                 |  |                      |  |                  |
 |                 +--+    Area 0            +--+                  |
 |                 | -------------------------- |     +--+         |
 |          +--+   |                            |     |  |         |
 |          |  |   |                            |     +--+         |
 | +--+     +--+   |                            |                  |
 | |  |            |                            |            +--+  |
 | +--+            |                            |            |  |  |
 |                 |                            |            +--+  |
 |       +--+      |                            |                  |
 |       |  |      |                            |     +--+         |
 |       +--+      |                            |     |  |         |
 |                 |                            |     +--+         |
 |                 |                            |                  |
 | Area 1          |                            |  Area 5          |
  -----------------                              ------------------
                 Figure 1: Inter-Area Path Computation

Dhody, et al. Experimental [Page 18] RFC 7897 Domain Subobjects for PCEP June 2016

 The AS Number is 100.
 If the ingress is in area 2, the egress is in area 4, and transit is
 through area 0, here are some possible ways a PCC can encode the IRO:
   +---------+ +---------+ +---------+
   |IRO      | |Sub-     | |Sub-     |
   |Object   | |object   | |object   |
   |Header   | |Area 0   | |Area 4   |
   |         | |         | |         |
   |         | |         | |         |
   +---------+ +---------+ +---------+
   or
   +---------+ +---------+ +---------+ +---------+
   |IRO      | |Sub-     | |Sub-     | |Sub-     |
   |Object   | |object   | |object   | |object   |
   |Header   | |Area 2   | |Area 0   | |Area 4   |
   |         | |         | |         | |         |
   |         | |         | |         | |         |
   +---------+ +---------+ +---------+ +---------+
   or
   +---------+ +---------+ +---------+ +---------+ +---------+
   |IRO      | |Sub-     | |Sub-     | |Sub-     | |Sub-     |
   |Object   | |object AS| |object   | |object   | |object   |
   |Header   | |100      | |Area 2   | |Area 0   | |Area 4   |
   |         | |         | |         | |         | |         |
   |         | |         | |         | |         | |         |
   +---------+ +---------+ +---------+ +---------+ +---------+
 The domain sequence can further include encompassing AS information
 in the AS subobject.

4.2. Inter-AS Path Computation

 In inter-AS path computation, where the ingress and egress belong to
 different ASes, the domain sequence could be represented using an
 ordered list of AS subobjects.  The domain sequence can further
 include decomposed area information in the area subobject.

Dhody, et al. Experimental [Page 19] RFC 7897 Domain Subobjects for PCEP June 2016

4.2.1. Example 1

 As shown in Figure 2, where AS has a single area, the AS subobject in
 the domain sequence can uniquely identify the next domain and PCE.
            AS A                AS E                AS C
       <------------->      <---------->      <------------->
                A4----------E1---E2---E3---------C4
               /           /                       \
             /            /                          \
           /            /       AS B                   \
         /            /      <---------->                \
   Ingress------A1---A2------B1---B2---B3------C1---C2------Egress
         \                                    /          /
           \                                /          /
             \                            /          /
               \                        /          /
                A3----------D1---D2---D3---------C3
                            <---------->
                                AS D
  • All ASes have one area (area 0)
                  Figure 2: Inter-AS Path Computation

Dhody, et al. Experimental [Page 20] RFC 7897 Domain Subobjects for PCEP June 2016

 If the ingress is in AS A, the egress is in AS C, and transit is
 through AS B, here are some possible ways a PCC can encode the IRO:
 +-------+ +-------+ +-------+
 |IRO    | |Sub-   | |Sub-   |
 |Object | |object | |object |
 |Header | |AS B   | |AS C   |
 |       | |       | |       |
 +-------+ +-------+ +-------+
 or
 +-------+ +-------+ +-------+ +-------+
 |IRO    | |Sub-   | |Sub-   | |Sub-   |
 |Object | |object | |object | |object |
 |Header | |AS A   | |AS B   | |AS C   |
 |       | |       | |       | |       |
 +-------+ +-------+ +-------+ +-------+
 or
 +-------+ +-------+ +-------+ +-------+ +-------+ +-------+ +-------+
 |IRO    | |Sub-   | |Sub-   | |Sub-   | |Sub-   | |Sub-   | |Sub-   |
 |Object | |object | |object | |object | |object | |object | |object |
 |Header | |AS A   | |Area 0 | |AS B   | |Area 0 | |AS C   | |Area 0 |
 |       | |       | |       | |       | |       | |       | |       |
 +-------+ +-------+ +-------+ +-------+ +-------+ +-------+ +-------+
 Note that to get a domain disjoint path, the ingress could also
 request the backup path with:
 +-------+ +-------+
 |XRO    | |Sub    |
 |Object | |Object |
 |Header | |AS B   |
 |       | |       |
 +-------+ +-------+

Dhody, et al. Experimental [Page 21] RFC 7897 Domain Subobjects for PCEP June 2016

 As described in Section 3.4.3, a domain subobject in IRO changes the
 domain information associated with the next set of subobjects till
 you encounter a subobject that changes the domain too.  Consider the
 following IRO:
 +-------+ +-------+ +-------+ +-------+ +-------+ +-------+
 |IRO    | |Sub-   | |Sub-   | |Sub-   | |Sub-   | |Sub-   |
 |Object | |object | |object | |object | |object | |object |
 |Header | |AS B   | |IP     | |IP     | |AS C   | |IP     |
 |       | |       | |B1     | |B3     | |       | |C1     |
 +-------+ +-------+ +-------+ +-------+ +-------+ +-------+
 On processing subobject "AS B", it changes the AS of the subsequent
 subobjects till we encounter another subobject "AS C" that changes
 the AS for its subsequent subobjects.
 Consider another IRO:
 +-------+ +-------+ +-------+ +-------+ +-------+
 |IRO    | |Sub-   | |Sub-   | |Sub-   | |Sub-   |
 |Object | |object | |object | |object | |object |
 |Header | |AS D   | |IP     | |IP     | |IP     |
 |       | |       | |D1     | |D3     | |C3     |
 +-------+ +-------+ +-------+ +-------+ +-------+
 Here as well, on processing "AS D", it changes the AS of the
 subsequent subobjects till you encounter another subobject "C3" that
 belongs in another AS and changes the AS for its subsequent
 subobjects.
 Further description for the boundary node and inter-AS link can be
 found in Section 4.3.

4.2.2. Example 2

 In Figure 3, AS 200 is made up of multiple areas.

Dhody, et al. Experimental [Page 22] RFC 7897 Domain Subobjects for PCEP June 2016

                |
                |  +-------------+                +----------------+
                |  |Area 2       |                |Area 4          |
                |  |         +--+|                |          +--+  |
                |  |         |  ||                |          | B|  |
                |  |  +--+   +--+|                |   +--+   +--+  |
                |  |  |  |       |                |   |  |         |
                |  |  +--+       |                |   +--+         |
                |  |        +--+ |                |          +--+  |
                |  |        |  | |                |          |  |  |
                |  |        +--+ |                |   +--+   +--+  |
                |  |  +--+       |+--------------+|   |  |         |
                |  |  |  |       +--+          +--+   +--+         |
 +-------------+|  |  +--+       |  |          |  |                |
 |             ||  |             +--+          +--+                |
 |         +--+||  +-------------+|              |+----------------+
 |         |  |||                 |     +--+     |
 |         +--+||                 |     |  |     |
 |    +--+     ||                 |     +--+     |
 |    |  |  +---+                +--+            |
 |    +--+  |   |----------------|  |            |
 |          +---+   Inter-AS     +--+   +--+     |
 |+--+         ||    Links        |     |  |     |
 ||A |      +---+                +--+   +--+     |
 |+--+      |   |----------------|  |            |
 |          +---+                +--+   +--+     |
 |    +--+     ||  +------------+ |     |  |     |+----------------+
 |    |  |     ||  |Area 3      +--+    +--+   +--+ Area 5         |
 |    +--+     ||  |            |  |           |  |                |
 |             ||  |            +--+           +--+                |
 |         +--+||  |       +--+ | |  Area 0      ||   +--+         |
 |         |  |||  |       |  | | +--------------+|   |  |         |
 |         +--+||  |       +--+ |                 |   +--+         |
 |             ||  |            |                 |          +--+  |
 |Area 0       ||  |   +--+     |                 |   +--+   |  |  |
 +-------------+|  |   |  |     |                 |   |  |   +--+  |
                |  |   +--+  +--+                 |   +--+         |
                |  |         |  |                 |                |
                |  |         +--+                 |          +--+  |
                |  |   +--+     |                 |          | C|  |
                |  |   |  |     |                 |          +--+  |
                |  |   +--+     |                 |                |
                |  |            |                 |                |
                |  +------------+                 +----------------+
                |
     AS 100     |  AS 200
                |
                  Figure 3: Inter-AS Path Computation

Dhody, et al. Experimental [Page 23] RFC 7897 Domain Subobjects for PCEP June 2016

 For LSP (A-B), where ingress A is in (AS 100, area 0), egress B is in
 (AS 200, area 4), and transit is through (AS 200, area 0), here are
 some possible ways a PCC can encode the IRO:
 +-------+ +-------+ +-------+ +-------+
 |IRO    | |Sub-   | |Sub-   | |Sub-   |
 |Object | |object | |object | |object |
 |Header | |AS 200 | |Area 0 | |Area 4 |
 |       | |       | |       | |       |
 +-------+ +-------+ +-------+ +-------+
 or
 +-------+ +-------+ +-------+ +-------+ +-------+ +-------+
 |IRO    | |Sub-   | |Sub-   | |Sub-   | |Sub-   | |Sub-   |
 |Object | |object | |object | |object | |object | |object |
 |Header | |AS 100 | |Area 0 | |AS 200 | |Area 0 | |Area 4 |
 |       | |       | |       | |       | |       | |       |
 +-------+ +-------+ +-------+ +-------+ +-------+ +-------+
 For LSP (A-C), where ingress A is in (AS 100, area 0), egress C is in
 (AS 200, area 5), and transit is through (AS 200, area 0), here are
 some possible ways a PCC can encode the IRO:
 +-------+ +-------+ +-------+ +-------+
 |IRO    | |Sub-   | |Sub-   | |Sub-   |
 |Object | |object | |object | |object |
 |Header | |AS 200 | |Area 0 | |Area 5 |
 |       | |       | |       | |       |
 +-------+ +-------+ +-------+ +-------+
 or
 +-------+ +-------+ +-------+ +-------+ +-------+ +-------+
 |IRO    | |Sub-   | |Sub-   | |Sub-   | |Sub-   | |Sub-   |
 |Object | |object | |object | |object | |object | |object |
 |Header | |AS 100 | |Area 0 | |AS 200 | |Area 0 | |Area 5 |
 |       | |       | |       | |       | |       | |       |
 +-------+ +-------+ +-------+ +-------+ +-------+ +-------+

Dhody, et al. Experimental [Page 24] RFC 7897 Domain Subobjects for PCEP June 2016

4.3. Boundary Node and Inter-AS Link

 A PCC or PCE can include additional constraints covering which
 boundary nodes (ABR or ASBR) or border links (inter-AS link) to be
 traversed while defining a domain sequence.  In which case, the
 boundary node or link can be encoded as a part of the domain
 sequence.
 Boundary nodes (ABR/ASBR) can be encoded using the IPv4 or IPv6
 prefix subobjects, usually with a loopback address of 32 and a prefix
 length of 128, respectively.  An inter-AS link can be encoded using
 the IPv4 or IPv6 prefix subobjects or unnumbered interface
 subobjects.
 For Figure 1, an ABR (say, 203.0.113.1) to be traversed can be
 specified in IRO as:
      +---------+ +---------+ +---------++---------+ +---------+
      |IRO      | |Sub-     | |Sub-     ||Sub-     | |Sub-     |
      |Object   | |object   | |object   ||object   | |object   |
      |Header   | |Area 2   | |IPv4     ||Area 0   | |Area 4   |
      |         | |         | |203.0.   ||         | |         |
      |         | |         | |112.1    ||         | |         |
      +---------+ +---------+ +---------++---------+ +---------+
 For Figure 3, an inter-AS link (say, 198.51.100.1 - 198.51.100.2) to
 be traversed can be specified as:
        +---------+  +---------+ +---------+ +---------+
        |IRO      |  |Sub-     | |Sub-     | |Sub-     |
        |Object   |  |object AS| |object   | |object AS|
        |Header   |  |100      | |IPv4     | |200      |
        |         |  |         | |198.51.  | |         |
        |         |  |         | |100.2    | |         |
        +---------+  +---------+ +---------+ +---------+

4.4. PCE Serving Multiple Domains

 A single PCE can be responsible for multiple domains; for example,
 PCE function deployed on an ABR could be responsible for multiple
 areas.  A PCE that can support adjacent domains can internally handle
 those domains in the domain sequence without any impact on the other
 domains in the domain sequence.

Dhody, et al. Experimental [Page 25] RFC 7897 Domain Subobjects for PCEP June 2016

4.5. P2MP

 [RFC7334] describes an experimental inter-domain P2MP path
 computation mechanism where the path domain tree is described as a
 series of domain sequences; an example is shown in the figure below:
                         +----------------+
                         |                |Domain D1
                         |        R       |
                         |                |
                         |        A       |
                         |                |
                         +-B------------C-+
                          /              \
                         /                \
                        /                  \
        Domain D2      /                    \ Domain D3
        +-------------D--+             +-----E----------+
        |                |             |                |
        |  F             |             |                |
        |          G     |             |       H        |
        |                |             |                |
        |                |             |                |
        +-I--------------+             +-J------------K-+
         /\                             /              \
        /  \                           /                \
       /    \                         /                  \
      /      \                       /                    \
     /        \                     /                      \
    /          \                   /                        \
   / Domain D4  \      Domain D5  /              Domain D6   \
 +-L-------------W+       +------P---------+      +-----------T----+
 |                |       |                |      |                |
 |                |       |  Q             |      |   U            |
 |  M        O    |       |         S      |      |                |
 |                |       |                |      |          V     |
 |          N     |       |   R            |      |                |
 +----------------+       +----------------+      +----------------+
                     Figure 4: Domain Tree Example
 The domain tree can be represented as a series of domain sequences:
 o  Domain D1, Domain D3, Domain D6
 o  Domain D1, Domain D3, Domain D5
 o  Domain D1, Domain D2, Domain D4

Dhody, et al. Experimental [Page 26] RFC 7897 Domain Subobjects for PCEP June 2016

 The domain sequence handling described in this document could be
 applied to the P2MP path domain tree.

4.6. Hierarchical PCE

 In case of H-PCE [RFC6805], the parent PCE can be requested to
 determine the domain sequence and return it in the path computation
 reply, using the ERO.  For the example in Section 4.6 of [RFC6805],
 the domain sequence can possibly appear as:
 +---------+ +---------+ +---------+ +---------+
 |ERO      | |Sub-     | |Sub-     | |Sub-     |
 |Object   | |object   | |object   | |object   |
 |Header   | |Domain 1 | |Domain 2 | |Domain 3 |
 |         | |         | |         | |         |
 |         | |         | |         | |         |
 +---------+ +---------+ +---------+ +---------+
 or
 +---------+ +---------+ +---------+
 |ERO      | |Sub-     | |Sub-     |
 |Object   | |object   | |object   |
 |Header   | |BN 21    | |Domain 3 |
 |         | |         | |         |
 |         | |         | |         |
 +---------+ +---------+ +---------+

5. Other Considerations

5.1. 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 MUST have higher precedence in selecting the
 next PCE in the inter-domain path computation procedures.

5.2. 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.

Dhody, et al. Experimental [Page 27] RFC 7897 Domain Subobjects for PCEP June 2016

 [RFC7898] extends the notion of abstract nodes by adding new
 subobjects for IGP areas and 4-byte AS numbers.  These subobjects can
 be included in ERO, XRO, or EXRS in RSVP-TE.
 In any case, subobject types defined in RSVP-TE are identical to the
 subobject types defined in the related documents in PCEP.

6. IANA Considerations

6.1. New Subobjects

 IANA maintains the "Path Computation Element Protocol (PCEP) Numbers"
 registry at <http://www.iana.org/assignments/pcep>.  Within this
 registry, IANA maintains two sub-registries:
 o  IRO Subobjects
 o  XRO Subobjects
 IANA has made identical additions to those registries as follows:
 Value   Description        Reference
 -----   ----------------   -------------------
 5       4-byte AS number   RFC 7897, [RFC7898]
 6       OSPF Area ID       RFC 7897, [RFC7898]
 7       IS-IS Area ID      RFC 7897, [RFC7898]
 Further, IANA has added a reference to this document to the new RSVP
 numbers that are registered by [RFC7898], as shown on
 <http://www.iana.org/assignments/rsvp-parameters>.

7. Security Considerations

 The protocol extensions defined in this document do not substantially
 change the nature of PCEP.  Therefore, the security considerations
 set out in [RFC5440] apply unchanged.  Note that further security
 considerations for the use of PCEP over TCP are presented in
 [RFC6952].
 This document specifies a representation of the domain sequence and
 new subobjects, which could be used in inter-domain PCE scenarios as
 explained in [RFC5152], [RFC5441], [RFC6805], [RFC7334], etc.  The
 security considerations set out in each of these mechanisms remain
 unchanged by the new subobjects and domain sequence representation in
 this document.

Dhody, et al. Experimental [Page 28] RFC 7897 Domain Subobjects for PCEP June 2016

 But the new subobjects do 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.
 Consequently, it is important that implementations conform to the
 relevant security requirements of [RFC5440].  These mechanisms
 include:
 o  Securing the PCEP session messages using TCP security techniques
    (Section 10.2 of [RFC5440]).  PCEP implementations SHOULD also
    consider the additional security provided by the TCP
    Authentication Option (TCP-AO) [RFC5925] or Transport Layer
    Security (TLS) [PCEPS].
 o  Authenticating the PCEP messages to ensure the messages are intact
    and sent from an authorized node (Section 10.3 of [RFC5440]).
 o  PCEP operates over TCP, so it is also important to secure the PCE
    and PCC against TCP denial-of-service attacks.  Section 10.7.1 of
    [RFC5440] outlines a number of mechanisms for minimizing the risk
    of TCP-based denial-of-service attacks against PCEs and PCCs.
 o  In inter-AS scenarios, attacks may be particularly significant
    with commercial- as well as service-level implications.
 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.

8. Manageability Considerations

8.1. Control of Function and Policy

 The exact behavior with regards to desired inclusion and exclusion of
 domains MUST be available for examination by an operator and MAY be
 configurable.  Manual configurations are needed to identify which
 PCEP peers understand the new domain subobjects defined in this
 document.

8.2. Information and Data Models

 A MIB module for management of the PCEP is being specified in a
 separate document [RFC7420].  This document does not imply any new
 extension to the current MIB module.

Dhody, et al. Experimental [Page 29] RFC 7897 Domain Subobjects for PCEP June 2016

8.3. Liveness Detection and Monitoring

 Mechanisms defined in this document do not imply any new liveness
 detection and monitoring requirements aside from those already listed
 in [RFC5440].

8.4. Verify Correct Operations

 Mechanisms defined in this document do not imply any new operation
 verification requirements aside from those already listed in
 [RFC5440].

8.5. Requirements on Other Protocols

 In case of per-domain path computation [RFC5152], where the full path
 of an inter-domain TE LSP cannot be determined (or is not determined)
 at the ingress node, a signaling message can use the domain
 identifiers.  The subobjects defined in this document SHOULD be
 supported by RSVP-TE.  [RFC7898] 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 aside from those already listed in
 [RFC5440].

8.6. Impact on Network Operations

 The mechanisms described in this document can provide the operator
 with the ability to exert finer and more specific control of the path
 computation by inclusion or exclusion of domain subobjects.  There
 may be some scaling benefit when a single domain subobject may
 substitute for many subobjects and can reduce the overall message
 size and processing.
 Backward compatibility issues associated with the new subobjects
 arise when a PCE does not recognize them, in which case PCE responds
 according to the rules for a malformed object as per [RFC5440].  For
 successful operations, the PCEs in the network would need to be
 upgraded.

Dhody, et al. Experimental [Page 30] RFC 7897 Domain Subobjects for PCEP June 2016

9. References

9.1. Normative References

 [ISO10589] International Organization for Standardization,
            "Information technology -- Telecommunications and
            information exchange between systems -- Intermediate
            System to Intermediate System intra-domain routeing
            information exchange protocol for use in conjunction with
            the protocol for providing the connectionless-mode network
            service (ISO 8473)", ISO/IEC 10589:2002, Second Edition,
            2002.
 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119,
            DOI 10.17487/RFC2119, March 1997,
            <http://www.rfc-editor.org/info/rfc2119>.
 [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
            and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
            Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
            <http://www.rfc-editor.org/info/rfc3209>.
 [RFC3473]  Berger, L., Ed., "Generalized Multi-Protocol Label
            Switching (GMPLS) Signaling Resource ReserVation Protocol-
            Traffic Engineering (RSVP-TE) Extensions", RFC 3473,
            DOI 10.17487/RFC3473, January 2003,
            <http://www.rfc-editor.org/info/rfc3473>.
 [RFC3477]  Kompella, K. and Y. Rekhter, "Signalling Unnumbered Links
            in Resource ReSerVation Protocol - Traffic Engineering
            (RSVP-TE)", RFC 3477, DOI 10.17487/RFC3477, January 2003,
            <http://www.rfc-editor.org/info/rfc3477>.
 [RFC5440]  Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
            Element (PCE) Communication Protocol (PCEP)", RFC 5440,
            DOI 10.17487/RFC5440, March 2009,
            <http://www.rfc-editor.org/info/rfc5440>.
 [RFC5441]  Vasseur, JP., Ed., 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,
            DOI 10.17487/RFC5441, April 2009,
            <http://www.rfc-editor.org/info/rfc5441>.

Dhody, et al. Experimental [Page 31] RFC 7897 Domain Subobjects for PCEP June 2016

 [RFC5521]  Oki, E., Takeda, T., and A. Farrel, "Extensions to the
            Path Computation Element Communication Protocol (PCEP) for
            Route Exclusions", RFC 5521, DOI 10.17487/RFC5521, April
            2009, <http://www.rfc-editor.org/info/rfc5521>.
 [RFC6805]  King, D., Ed. and A. Farrel, Ed., "The Application of the
            Path Computation Element Architecture to the Determination
            of a Sequence of Domains in MPLS and GMPLS", RFC 6805,
            DOI 10.17487/RFC6805, November 2012,
            <http://www.rfc-editor.org/info/rfc6805>.
 [RFC7896]  Dhody, D., "Update to the Include Route Object (IRO)
            Specification in the Path Computation Element
            Communication Protocol (PCEP)", RFC 7896,
            DOI 10.17487/RFC7896, June 2016,
            <http://www.rfc-editor.org/info/rfc7896>.
 [RFC7898]  Dhody, D., Palle, U., Kondreddy, V., and R. Casellas,
            "Domain Subobjects for Resource Reservation Protocol -
            Traffic Engineering (RSVP-TE)", RFC 7898,
            DOI 10.17487/RFC7898, June 2016,
            <http://www.rfc-editor.org/info/rfc7898>.

9.2. Informative References

 [PCEPS]    Lopez, D., Dios, O., Wu, W., and D. Dhody, "Secure
            Transport for PCEP", Work in Progress,
            draft-ietf-pce-pceps-09, November 2015.
 [RFC4655]  Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
            Element (PCE)-Based Architecture", RFC 4655,
            DOI 10.17487/RFC4655, August 2006,
            <http://www.rfc-editor.org/info/rfc4655>.
 [RFC4726]  Farrel, A., Vasseur, J., and A. Ayyangar, "A Framework for
            Inter-Domain Multiprotocol Label Switching Traffic
            Engineering", RFC 4726, DOI 10.17487/RFC4726, November
            2006, <http://www.rfc-editor.org/info/rfc4726>.
 [RFC4873]  Berger, L., Bryskin, I., Papadimitriou, D., and A. Farrel,
            "GMPLS Segment Recovery", RFC 4873, DOI 10.17487/RFC4873,
            May 2007, <http://www.rfc-editor.org/info/rfc4873>.
 [RFC4874]  Lee, CY., Farrel, A., and S. De Cnodder, "Exclude Routes -
            Extension to Resource ReserVation Protocol-Traffic
            Engineering (RSVP-TE)", RFC 4874, DOI 10.17487/RFC4874,
            April 2007, <http://www.rfc-editor.org/info/rfc4874>.

Dhody, et al. Experimental [Page 32] RFC 7897 Domain Subobjects for PCEP June 2016

 [RFC5152]  Vasseur, JP., Ed., Ayyangar, A., Ed., and R. Zhang, "A
            Per-Domain Path Computation Method for Establishing Inter-
            Domain Traffic Engineering (TE) Label Switched Paths
            (LSPs)", RFC 5152, DOI 10.17487/RFC5152, February 2008,
            <http://www.rfc-editor.org/info/rfc5152>.
 [RFC5520]  Bradford, R., Ed., Vasseur, JP., and A. Farrel,
            "Preserving Topology Confidentiality in Inter-Domain Path
            Computation Using a Path-Key-Based Mechanism", RFC 5520,
            DOI 10.17487/RFC5520, April 2009,
            <http://www.rfc-editor.org/info/rfc5520>.
 [RFC5886]  Vasseur, JP., Ed., Le Roux, JL., and Y. Ikejiri, "A Set of
            Monitoring Tools for Path Computation Element (PCE)-Based
            Architecture", RFC 5886, DOI 10.17487/RFC5886, June 2010,
            <http://www.rfc-editor.org/info/rfc5886>.
 [RFC5925]  Touch, J., Mankin, A., and R. Bonica, "The TCP
            Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
            June 2010, <http://www.rfc-editor.org/info/rfc5925>.
 [RFC6793]  Vohra, Q. and E. Chen, "BGP Support for Four-Octet
            Autonomous System (AS) Number Space", RFC 6793,
            DOI 10.17487/RFC6793, December 2012,
            <http://www.rfc-editor.org/info/rfc6793>.
 [RFC6952]  Jethanandani, M., Patel, K., and L. Zheng, "Analysis of
            BGP, LDP, PCEP, and MSDP Issues According to the Keying
            and Authentication for Routing Protocols (KARP) Design
            Guide", RFC 6952, DOI 10.17487/RFC6952, May 2013,
            <http://www.rfc-editor.org/info/rfc6952>.
 [RFC7334]  Zhao, Q., Dhody, D., King, D., Ali, Z., and R. Casellas,
            "PCE-Based Computation Procedure to Compute Shortest
            Constrained Point-to-Multipoint (P2MP) Inter-Domain
            Traffic Engineering Label Switched Paths", RFC 7334,
            DOI 10.17487/RFC7334, August 2014,
            <http://www.rfc-editor.org/info/rfc7334>.
 [RFC7420]  Koushik, A., Stephan, E., Zhao, Q., King, D., and J.
            Hardwick, "Path Computation Element Communication Protocol
            (PCEP) Management Information Base (MIB) Module",
            RFC 7420, DOI 10.17487/RFC7420, December 2014,
            <http://www.rfc-editor.org/info/rfc7420>.

Dhody, et al. Experimental [Page 33] RFC 7897 Domain Subobjects for PCEP June 2016

Acknowledgments

 The authors would like to especially thank Adrian Farrel for his
 detailed reviews as well as providing text to be included in the
 document.
 Further, we would like to thank Pradeep Shastry, Suresh Babu, Quintin
 Zhao, Fatai Zhang, Daniel King, Oscar Gonzalez, Chen Huaimo,
 Venugopal Reddy, Reeja Paul, Sandeep Boina, Avantika Sergio Belotti,
 and Jonathan Hardwick for their useful comments and suggestions.
 Thanks to Jonathan Hardwick for shepherding this document.
 Thanks to Deborah Brungard for being the responsible AD.
 Thanks to Amanda Baber for the IANA review.
 Thanks to Joel Halpern for the Gen-ART review.
 Thanks to Klaas Wierenga for the SecDir review.
 Thanks to Spencer Dawkins and Barry Leiba for comments during the
 IESG review.

Dhody, et al. Experimental [Page 34] RFC 7897 Domain Subobjects for PCEP June 2016

Authors' Addresses

 Dhruv Dhody
 Huawei Technologies
 Divyashree Techno Park, Whitefield
 Bangalore, Karnataka  560066
 India
 Email: dhruv.ietf@gmail.com
 Udayasree Palle
 Huawei Technologies
 Divyashree Techno Park, Whitefield
 Bangalore, Karnataka  560066
 India
 Email: udayasree.palle@huawei.com
 Ramon Casellas
 CTTC
 Av. Carl Friedrich Gauss n7
 Castelldefels, Barcelona  08860
 Spain
 Email: ramon.casellas@cttc.es

Dhody, et al. Experimental [Page 35]

/data/webs/external/dokuwiki/data/pages/rfc/rfc7897.txt · Last modified: 2016/06/15 22:00 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki