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PCE Working Group                                                H. Chen
Internet-Draft                                                  D. Dhody
Intended status: Informational                       Huawei Technologies
Expires: November 1, 2018                                 April 30, 2018


The Applicability of the PCE to Computing Protection and Recovery Paths
              for Single Domain and Multi-Domain Networks.
               draft-chen-pce-protection-applicability-12

Abstract

   The Path Computation Element (PCE) provides path computation
   functions in support of traffic engineering in Multiprotocol Label
   Switching (MPLS) and Generalized MPLS (GMPLS) networks.

   A link or node failure can significantly impact network services in
   large-scale networks.  Therefore it is important to ensure the
   survivability of large scale networks which consist of various
   connections provided over multiple interconnected networks with
   varying technologies.

   This document examines the applicability of the PCE architecture,
   protocols, and procedures for computing protection paths and
   restoration services, for single and multi-domain networks.

   This document also explains the mechanism of Fast Re-Route (FRR)
   where a point of local repair (PLR) needs to find the appropriate
   merge point (MP) to do bypass path computation using PCE.

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 November 1, 2018.

Copyright Notice



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   Copyright (c) 2018 IETF Trust and the persons identified as the
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   described in the Simplified BSD License.







































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Domains  . . . . . . . . . . . . . . . . . . . . . . . . .  4
       1.1.1.  Inter-domain LSPs  . . . . . . . . . . . . . . . . . .  5
     1.2.  Recovery . . . . . . . . . . . . . . . . . . . . . . . . .  5
     1.3.  Requirements Language  . . . . . . . . . . . . . . . . . .  5
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Path Computation Element Architecture Considerations . . . . .  7
     3.1.  Online Path Computation  . . . . . . . . . . . . . . . . .  7
     3.2.  Offline Path Computation . . . . . . . . . . . . . . . . .  7
   4.  Protection Service Traffic Engineering . . . . . . . . . . . .  8
     4.1.  Path Computation . . . . . . . . . . . . . . . . . . . . .  8
     4.2.  Bandwidth Reservation  . . . . . . . . . . . . . . . . . .  8
     4.3.  Disjoint Path  . . . . . . . . . . . . . . . . . . . . . .  8
     4.4.  Service Preemption . . . . . . . . . . . . . . . . . . . .  8
     4.5.  Share Risk Link Groups . . . . . . . . . . . . . . . . . .  8
     4.6.  Multi-Homing . . . . . . . . . . . . . . . . . . . . . . .  8
       4.6.1.  Ingress and Egress Protection  . . . . . . . . . . . .  9
   5.  Packet Protection Applications . . . . . . . . . . . . . . . .  9
     5.1.  Single Domain Service Protection . . . . . . . . . . . . . 10
     5.2.  Multi-domain Service Protection  . . . . . . . . . . . . . 10
     5.3.  Backup Path Computation  . . . . . . . . . . . . . . . . . 10
     5.4.  Fast Reroute (FRR) Path Computation  . . . . . . . . . . . 10
       5.4.1.  Methods to find MP and calculate the optimal
               backup path  . . . . . . . . . . . . . . . . . . . . . 11
         5.4.1.1.  Intra-domain node protection . . . . . . . . . . . 12
         5.4.1.2.  Boundary node protection . . . . . . . . . . . . . 12
     5.5.  Point-to-Multipoint Path Protection  . . . . . . . . . . . 15
   6.  Optical Protection Applications  . . . . . . . . . . . . . . . 16
     6.1.  ASON Applicability . . . . . . . . . . . . . . . . . . . . 16
     6.2.  Multi-domain Restoration . . . . . . . . . . . . . . . . . 16
   7.  Path and Service Protection Gaps . . . . . . . . . . . . . . . 16
   8.  Manageability Considerations . . . . . . . . . . . . . . . . . 16
     8.1.  Control of Function and Policy . . . . . . . . . . . . . . 16
     8.2.  Information and Data Models  . . . . . . . . . . . . . . . 16
     8.3.  Liveness Detection and Monitoring  . . . . . . . . . . . . 16
     8.4.  Verify Correct Operations  . . . . . . . . . . . . . . . . 16
     8.5.  Requirements On Other Protocols  . . . . . . . . . . . . . 16
     8.6.  Impact On Network Operations . . . . . . . . . . . . . . . 16
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 16
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 16
   11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 17
   12. Acknowledgement  . . . . . . . . . . . . . . . . . . . . . . . 17
   13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
     13.1. Normative References . . . . . . . . . . . . . . . . . . . 17
     13.2. Informative References . . . . . . . . . . . . . . . . . . 17




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1.  Introduction

   Network survivability remains a major concern for network operators
   and service providers, particularly as expanding applications such as
   private and Public Cloud drive increasingly more traffic across
   longer ranges, to a wider number of users.  A variety of well-known
   pre-planned protection and post-fault recovery schemes have been
   developed for IP, MPLS and GMPLS networks.

   The Path Computation Element (PCE) [RFC4655] can be used to perform
   complex path computation in large single domain, multi-domain and
   multi-layered networks.  The PCE can also be used to compute a
   variety of restoration and protection paths and services.

   This document examines the applicability of the PCE architecture,
   protocols, and protocol extensions for computing protection paths and
   restoration services.

1.1.  Domains

   A domain can be defined as a separate administrative, geographic, or
   switching 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 Antonymous System
   (AS) or an Interior Gateway Protocol (IGP) area (as per [RFC4726] and
   [RFC4655]), or specific switching environment.

   In the context of GMPLS, a particularly important example of a domain
   is the Automatically Switched Optical Network (ASON) subnetwork
   [G-8080].  In this case, computation of an end-to-end path requires
   the selection of nodes and links within a parent domain where some
   nodes may, in fact, be subnetworks.  Furthermore, a domain might be
   an ASON routing area [G-7715].  A PCE may perform the path
   computation function of an ASON routing controller as described in
   [G-7715-2].

   It is assumed that the PCE architecture should be applied to small
   inter-domain topologies and not to solve route computation issues
   across large groups of domains, I.E. the entire Internet.

   Most existing protocol mechanisms for network survivability have
   focused on single-domain scenarios.  Multi-domain scenarios are much
   more complex and challenging as domain topology information is
   typically not shared outside each specific domain.

   Therefore multi-domain survivability is a key requirement for today's
   complex networks.  It is important to develop more adaptive multi-
   domain recovery solutions for various failure scenarios.



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1.1.1.  Inter-domain LSPs

   Three signaling options are defined for setting up an inter-area or
   inter-AS LSP [RFC4726]:

   o  Contiguous LSP

   o  Stitched LSP

   o  Nested LSP

1.2.  Recovery

   Typically traffic-engineered networks such as MPLS-TE and GMPLS, use
   protection and recovery mechanisms based on the pre-established use
   of a packet or optical LSP and/or the availability of spare resources
   and the network topology.

1.3.  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].

   In this document, these words will appear with that interpretation
   only when in ALL CAPS.  Lower case uses of these words are not to be
   interpreted as carrying [RFC2119] significance.

2.  Terminology

   The following terminology is used in this document.

   ABR:  Area Border Router.  Router used to connect two IGP areas
      (Areas in OSPF or levels in IS-IS).

   ASBR:  Autonomous System Border Router.  Router used to connect
      together ASes of the same or different service providers via one
      or more inter-AS links.

   BN:  Boundary Node (BN).  A boundary node is either an ABR in the
      context of inter-area Traffic Engineering or an ASBR in the
      context of inter-AS Traffic Engineering.

   CPS:  Confidential Path Segment.  A segment of a path that contains
      nodes and links that the AS policy requires not to be disclosed
      outside the AS.





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   CSP:  Communication Service Provide.

   CSPF:  Constrained Shorted Path First Algorithm.

   ERO:  Explicit Route Object.

   FRR:  Fast Re-Route.

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

   Inter-area TE LSP:  A TE LSP whose path transits through two or more
      IGP areas.

   Inter-AS TE LSP:  A TE LSP whose path transits through two or more
      ASs or sub-ASs (BGP confederations).

   IS-IS:  Intermediate System to Intermediate System.

   LSP:  Label Switched Path.

   LSR:  Label Switching Router.

   MP:  Merge Point.  The LSR where one or more backup tunnels rejoin
      the path of the protected LSP downstream of the potential failure.

   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.

   PKS:  Path Key Subobject.  A subobject of an Explicit Route Object or
      Record Route Object that encodes a CPS so as to preserve
      confidentiality.

   PLR:  Point of Local Repair.  The head-end LSR of a backup tunnel or
      a detour LSP.

   RRO:  Record Route Object.






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   RSVP:  Resource Reservation Protocol.

   SRLG:  Shared Risk Link Group.

   TE:  Traffic Engineering.

   TED:  Traffic Engineering Database, which contains the topology and
      resource information of the domain.  The TED may be fed by
      Interior Gateway Protocol (IGP) extensions or potentially by other
      means.

   This document also uses the terminology defined in [RFC4655] and
   [RFC5440].

3.  Path Computation Element Architecture Considerations

   For the purpose of this document it is assumed that the path
   computation is the sole responsibility of the PCE as per the
   architecture defined in [RFC4655].  When a path is required the Path
   Computation Client (PCC) will send a request to the PCE.  The PCE
   will apply the required constraints and compute a path and return a
   response to the PCC.  In the context of this document it may be
   necessary for the PCE to co-operate with other PCEs in adjacent
   domains (as per BRPC [RFC5441]) or cooperate with the Parent PCE (as
   per RFC 6805).

   A PCE may be used to compute end-to-end paths across single or
   multiple domains.  Multiple PCEs may be dedicated to each area to
   provide sufficient path computation capacity and redundancy for each
   domain.

   During path computation [RFC5440], a PCC request may contain backup
   LSP requirements in order to setup in the same time the primary and
   backup LSPs.  This request is known as dependent path computations.
   A typical dependent request for a primary and backup service would
   request that the computation assign a set of diverse paths, so both
   services are disjointed from each other.

3.1.  Online Path Computation

   Online path computation is performed on-demand as nodes in the
   network determine that they need to know the paths to use for
   services.

3.2.  Offline Path Computation

   Offline path computation is performed ahead of time, before the LSP
   setup is requested.  That means that it is requested by, or performed



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   as part of, a management application.

   This method of computation allows the optimal placement of services
   and explicit control of services.  A Communication Service Provide
   (CSP) can plan where new protection services will be placed ahead of
   time.  Furthermore by computing paths offline specific scenarios can
   be considered and a global view of network resources is available.

   Finally, offline path computation provides a method to compute
   protection paths in the event of a single, or multiple, link
   failures.  This allows the placement of backup services in the event
   of catastrophic network failures.

4.  Protection Service Traffic Engineering

4.1.  Path Computation

   This document describes how the PCE architecture defined in [RFC4655]
   may be utilized to compute protection and recovery paths for critical
   network services.  In the context of this document (inter-domain) it
   may be necessary for the PCE to co-operate with other PCEs in
   adjacent domains (as per BRPC [RFC5441]) or cooperate with the Parent
   PCE (as per RFC 6805).

4.2.  Bandwidth Reservation

4.3.  Disjoint Path

   Disjoint paths are required for end-to-end protection services.  A
   backup service may be required to be fully disjoint from the primary
   service, link disjoint (allowing common nodes on the paths), or best-
   effort disjoint (allowing shared links or nodes when no other path
   can be found).

4.4.  Service Preemption

4.5.  Share Risk Link Groups

4.6.  Multi-Homing

   Networks constructed from multi-areas or multi-AS environments may
   have multiple interconnect points (multi-homing).  End-to-end path
   computations may need to use different interconnect points to avoid
   single point failures disrupting primary and backup services.

   Domain and path diversity may also be required when computing end-to-
   end paths.  Domain diversity should facilitate the selection of paths
   that share ingress and egress domains, but do not share transit



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   domains.  Therefore, there must be a method allowing the inclusion or
   exclusion of specific domains when computing end-to-end paths.

4.6.1.  Ingress and Egress Protection

   An end-to-end primary service carried by a primary TE LSP from a
   primary ingress node to a primary egress node may need to be
   protected against the failures in the ingress and the egress.  In
   this case, a backup ingress and a backup egress are required, which
   are different from the primary ingress and the primary egress
   respectively.  The backup ingress should be in the same domain as the
   primary ingress, and the backup egress should be in the same domain
   as the primary egress.

   A source of the service traffic may be sent to both the primary
   ingress and the backup ingress (dual-homing).  The source may not be
   in the same domain as the primary ingress and the backup ingress.
   When the primary ingress fails, the service traffic is delivered
   through the backup ingress.

   A receiver of the service traffic may be connected to both the
   primary egress and the backup egress (dual-homing).  The receiver may
   not be in the same domain as the primary egress and the backup
   egress.  When the primary egress fails, the receiver gets the service
   traffic from the backup egress.

5.  Packet Protection Applications

   Network survivability is a key objective for CSPs, particularly as
   expanding revenue services (cloud and data center applications) are
   increasing exponentially.

   Pre-fault paths are pre-computed and protection resources are
   reserved a priory for rapid recovery.  In the event of a network
   failure on the primary path, the traffic is fast switched to the
   backup path.  These pre-provisioned mechanisms are capable of
   ensuring protection against single link failures.

   Post-fault restoration schemes are reactive and require a reactive
   routing procedure to set up new working paths in the event of a
   failure.  Post fault restoration can significantly impact network
   services as they are typically impacted by longer restoration delays
   and cannot guarantee recovery of a service.  However, they are much
   more network resource efficient and are capable of handling multi-
   failure situations.






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5.1.  Single Domain Service Protection

   A variety of pre-planned protection and post-fault restoration
   recovery schemes are available for single domain MPLS and GMPLS
   networks, these include:

   o  Path Recovery

   o  Path Segment Recovery

   o  Local Recovery (Fast Reroute)

5.2.  Multi-domain Service Protection

   Typically network survivability has focused on single-domain
   scenarios.  By contrast, broader multi-domain scenarios are much more
   challenging as no single entity has a global view of topology
   information.  As a result, multi-domain survivability is very
   important.

   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 LSPs.

5.3.  Backup Path Computation

   A PCE can be used to compute backup paths in the context of fast
   reroute protection of TE LSPs.  In this model, all backup TE LSPs
   protecting a given facility are computed in a coordinated manner by a
   PCE.  This allows complete bandwidth sharing between backup tunnels
   protecting independent elements, while avoiding any extensions to TE
   LSP signaling.  Both centralized and distributed computation models
   are applicable.  In the distributed case each LSR can be a PCE to
   compute the paths of backup tunnels to protect against the failure of
   adjacent network links or nodes.

5.4.  Fast Reroute (FRR) Path Computation

   As stated in [RFC4090], there are two independent methods (one-to-one
   backup and facility backup) of doing fast reroute (FRR).  PCE can be
   used to compute backup path for both of the methods.  Cooperating
   PCEs may be used to compute inter-domain backup path.

   In case of one to one backup method, the destination MUST be the
   tail-end of the protected LSP.  Whereas for facility backup,
   destination MUST be the address of the merge point (MP) from the



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   corresponding point of local repair (PLR).  The problem of finding
   the MP using the interface addresses or node-ids present in Record
   Route Object (RRO) of protected path can be easily solved in the case
   of a single Interior Gateway Protocol (IGP) area because the PLR has
   the complete Traffic Engineering Database (TED).  Thus, the PLR can
   unambiguously determine -

   o  The MP address regardless of RRO IPv4 or IPv6 sub-objects
      (interface address or LSR ID).

   o  Does a backup tunnel intersecting a protected TE LSP on MP node
      exist?  This is the case where facility backup tunnel already
      exists either due to another protected TE LSP or it is pre-
      configured.

   It is complex for a PLR to find the MP in case of boundary node
   protection for computing a bypass path because the PLR doesn't have
   the full TED visibility.  When confidentiality (via path key)
   [RFC5520] is enabled, finding MP is very complex.

   This document describes the mechanism to find MP and to setup bypass
   tunnel to protect a boundary node.

5.4.1.  Methods to find MP and calculate the optimal backup path

   The Merge Point (MP) address is required at the PLR in order to
   select a bypass tunnel intersecting a protected Traffic Engineering
   Label Switched Path (TE LSP) on a downstream LSR.

   Some implementations may choose to pre-configure a bypass tunnel on
   PLR with destination address as MP.  MP's Domain to be traversed by
   bypass path can be administratively configured or learned via some
   other means (ex Hierarchical PCE (HPCE) RFC 6805).  Path Computation
   Client (PCC) on PLR can request its local PCE to compute bypass path
   from PLR to MP, excluding links and node between PLR and MP.  At PLR
   once primary tunnel is up, a pre-configured bypass tunnel is bound to
   the primary tunnel, note that multiple bypass tunnels can also exist.

   Most implementations may choose to create a bypass tunnel on PLR
   after primary tunnel is signaled with Record Route Object (RRO) being
   present in primary path's Resource Reservation Protocol (RSVP) Path
   Reserve message.  MP address has to be determined (described below)
   to create a bypass tunnel.  PCC on PLR can request its local PCE to
   compute bypass path from PLR to MP, excluding links and node between
   PLR and MP.






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5.4.1.1.  Intra-domain node protection

              [R1]----[R2]----[R3]----[R4]---[R5]
                        \             /
                        [R6]--[R7]--[R8]

             Protected LSP Path: [R1->R2->R3->R4->R5]
             Bypass LSP Path:    [R2->R6->R7->R8->R4]


                     Figure 1: Node Protection for R3

   In Figure 1, R2 has to build a bypass tunnel that protects against
   the failure of link [R2->R3] and node [R3].  R2 is PLR and R4 is MP
   in this case.  Since, both PLR and MP belong to the same area.  The
   problem of finding the MP using the interface addresses or node-ids
   can be easily solved.  Thus, the PLR can unambiguously find the MP
   address regardless of RRO IPv4 or IPv6 sub-objects (interface address
   or LSR ID) and also determine whether a backup tunnel intersecting a
   protected TE LSP on a downstream node (MP) already exists.

   TED on PLR will have the information of both R2 and R4, which can be
   used to find MP's TE router IP address and compute optimal backup
   path from R2 to R4, excluding link [R2->R3] and node [R3].

   Thus, RSVP-TE can signal bypass tunnel along the computed path.

5.4.1.2.  Boundary node protection

5.4.1.2.1.  Area Boundary Router (ABR) node protection

                             |
                   PCE-1     |     PCE-2
                             |
                  IGP area 0 |  IGP area 1
                             |
                             |
            [R1]----[R2]----[R3]----[R4]---[R5]
                    \        |       /
                    [R6]--[R7]--[R8]
                             |
                             |
                             |

             Protected LSP Path: [R1->R2->R3->R4->R5]
             Bypass LSP Path:    [R2->R6->R7->R8->R4]





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                  Figure 2: Node Protection for R3 (ABR)

   In Figure 2, cooperating PCE(s) (PCE-1 and PCE-2) have computed the
   primary LSP Path [R1->R2->R3->R4->R5] and provided to R1 (PCC).

   R2 has to build a bypass tunnel that protects against the failure of
   link [R2->R3] and node [R3].  R2 is PLR and R4 is MP.  Both PLR and
   MP are in different area.  TED on PLR doesn't have the information of
   R4.

   The problem of finding the MP address in a network with inter-domain
   TE LSP is solved by inserting a node-id sub-object [RFC4561] in the
   RRO object carried in the RSVP Path Reserve message.  PLR can find
   out the MP from the RRO it has received in Path Reserve message from
   its downstream LSR.

   But the computation of optimal backup path from R2 to R4, excluding
   link [R2->R3] and node [R3] is not possible with running of
   Constrained Shortest Path First (CSPF) algorithm locally at R2.  PCE
   can be used to compute backup path in this case.  R2 acting as PCC on
   PLR can request PCE-1 to compute bypass path from PLR(R2) to MP(R4),
   excluding link [R2->R3] and node [R3].  PCE MAY use inter-domain path
   computation mechanism (like HPCE (RFC 6805) etc) when the domain
   information of MP is unknown at PLR.  Further, RSVP-TE can signal
   bypass tunnel along the computed path.

5.4.1.2.2.  Autonomous System Border Router (ASBR) node protection

                              |        |
                        PCE-1 |        | PCE-2
                              |        |
                       AS 100 |        | AS 200
                              |        |
                              |        |
                   [R1]----[R2]-------[R3]---------[R4]---[R5]
                              |\       |            /
                              | +-----[R6]--[R7]--[R8]
                              |        |
                              |        |

             Protected LSP Path: [R1->R2->R3->R4->R5]
             Bypass LSP Path:    [R2->R6->R7->R8->R4]


                  Figure 3: Node Protection for R3 (ASBR)

   In Figure 3, Links [R2->R3] and [R2->R6] are inter-AS links.  IGP
   extensions ([RFC5316] and [RFC5392]) describe the flooding of



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   inter-AS TE information for inter-AS path computation.  Cooperating
   PCE(s) (PCE-1 and PCE-2) have computed the primary LSP Path
   [R1->R2->R3->R4->R5] and provided to R1 (PCC).

   R2 is PLR and R4 is MP.  Both PLR and MP are in different AS.  TED on
   PLR doesn't have the information of R4.

   The address of MP can be found using node-id sub-object [RFC4561] in
   the RRO object carried in the RSVP Path Reserve message.  And
   Cooperating PCEs could be used to compute the inter-AS bypass path.
   Thus ASBR boundary node protection is similar to ABR protection.

5.4.1.2.3.  Boundary node protection with Path-Key Confidentiality

   [RFC5520] defines a mechanism to hide the contents of a segment of a
   path, called the Confidential Path Segment (CPS).  The CPS may be
   replaced by a path-key that can be conveyed in the PCE Communication
   Protocol (PCEP) and signaled within in a Resource Reservation
   Protocol TE (RSVP-TE) explicit route object.

   [RFC5553] states that, when the signaling message crosses a domain
   boundary, the path segment that needs to be hidden (that is, a CPS)
   MAY be replaced in the RRO with a PKS.  Note that RRO in Resv message
   carries the same PKS as originally signaled in the ERO of the Path
   message.

5.4.1.2.3.1.  Area Boundary Router (ABR) node protection

                             |
                   PCE-1     |     PCE-2
                             |
                  IGP area 0 |  IGP area 1
                             |
                             |
            [R1]----[R2]----[R3]----[R4]---[R5]---[R9]
                    \        |       /
                    [R6]--[R7]--[R8]
                             |
                             |
                             |


            Figure 4: Node Protection for R3 (ABR) and Path-Key

   In Figure 4, when path-key is enabled, cooperating PCE(s) (PCE-1 and
   PCE-2) have computed the primary LSP Path [R1->R2->R3->PKS->R9] and
   provided to R1 (PCC).




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   When the ABR node (R3) replaces the CPS with PKS (as originally
   signaled) during the Reserve message handling, it MAY also add the
   immediate downstream node-id (R4) (so that the PLR (R2) can identify
   the MP (R4)).  Further the PLR (R2) SHOULD remove the MP node-id (R4)
   before sending the Reserve message upstream to head end router.

   Once MP is identified, the backup path computation using PCE is as
   described earlier.  (Section 5.4.1.2.1)

5.4.1.2.3.2.  Autonomous System Border Router (ASBR) node protection

                              |        |
                        PCE-1 |        | PCE-2
                              |        |
                       AS 100 |        | AS 200
                              |        |
                              |        |
                   [R1]----[R2]-------[R3]---------[R4]---[R5]
                              |\       |            /
                              | +-----[R6]--[R7]--[R8]
                              |        |
                              |        |



                  Figure 5: Node Protection for R3 (ASBR)

   The address of MP can be found using the same mechanism as explained
   above.  Thus ASBR boundary node protection is similar to ABR
   protection.

5.5.  Point-to-Multipoint Path Protection

   A PCE utilizing the extensions outlined in [RFC6006] (Extensions to
   PCEP for Point-to-Multipoint Traffic Engineering Label Switched
   Paths), can be used to compute point-to-multipoint (P2MP) paths.  A
   PCC requesting path computation for a primary and backup path can
   request that these dependent computations use diverse paths.
   Furthermore, the specification also defines two new options for P2MP
   path dependent computation requests.  The first option allows the PCC
   to request that the PCE should compute a secondary P2MP path tree
   with partial path diversity for specific leaves or a specific source-
   to-leaf (sub-path to the primary P2MP path tree.  The second option,
   allows the PCC to request that partial paths should be link direction
   diverse.






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6.  Optical Protection Applications

6.1.  ASON Applicability

6.2.  Multi-domain Restoration

7.  Path and Service Protection Gaps

8.  Manageability Considerations

8.1.  Control of Function and Policy

   TBD

8.2.  Information and Data Models

   TBD

8.3.  Liveness Detection and Monitoring

   TBD

8.4.  Verify Correct Operations

   TBD

8.5.  Requirements On Other Protocols

   TBD

8.6.  Impact On Network Operations

   TBD

9.  Security Considerations

   This document does not introduce new security issues.  However, MP's
   node-id is carried as subobject in RRO across domain.  This
   relaxation is required to find MP in case of BN protection.  The
   security considerations pertaining to the [RFC3209], [RFC4090] and
   [RFC5440] protocols remain relevant.

10.  IANA Considerations

   This document makes no requests for IANA action.






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11.  Contributors



      Venugopal Reddy Kondreddy
      Huawei Technologies
      Leela Palace
      Bangalore, Karnataka  560008
      INDIA

      EMail: venugopalreddyk@huawei.com



12.  Acknowledgement

   We would like to thank Daniel King, Udayashree Palle, Sandeep Boina &
   Reeja Paul for their useful comments and suggestions.

13.  References

13.1.  Normative References

   [RFC2119]   Bradner, S., "Key words for use in RFCs to Indicate
               Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
               RFC2119, March 1997,
               <https://www.rfc-editor.org/info/rfc2119>.

13.2.  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, DOI 10.17487/RFC3209, December 2001,
               <https://www.rfc-editor.org/info/rfc3209>.

   [RFC4090]   Pan, P., Ed., Swallow, G., Ed., and A. Atlas, Ed., "Fast
               Reroute Extensions to RSVP-TE for LSP Tunnels", RFC 4090,
               DOI 10.17487/RFC4090, May 2005,
               <https://www.rfc-editor.org/info/rfc4090>.

   [RFC4561]   Vasseur, J., Ed., Ali, Z., and S. Sivabalan, "Definition
               of a Record Route Object (RRO) Node-Id Sub-Object",
               RFC 4561, DOI 10.17487/RFC4561, June 2006,
               <https://www.rfc-editor.org/info/rfc4561>.

   [RFC4655]   Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
               Element (PCE)-Based Architecture", RFC 4655,
               DOI 10.17487/RFC4655, August 2006,



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               <https://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, <https://www.rfc-editor.org/info/rfc4726>.

   [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, <https://www.rfc-editor.org/info/rfc5152>.

   [RFC5316]   Chen, M., Zhang, R., and X. Duan, "ISIS Extensions in
               Support of Inter-Autonomous System (AS) MPLS and GMPLS
               Traffic Engineering", RFC 5316, DOI 10.17487/RFC5316,
               December 2008, <https://www.rfc-editor.org/info/rfc5316>.

   [RFC5392]   Chen, M., Zhang, R., and X. Duan, "OSPF Extensions in
               Support of Inter-Autonomous System (AS) MPLS and GMPLS
               Traffic Engineering", RFC 5392, DOI 10.17487/RFC5392,
               January 2009, <https://www.rfc-editor.org/info/rfc5392>.

   [RFC5440]   Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
               Element (PCE) Communication Protocol (PCEP)", RFC 5440,
               DOI 10.17487/RFC5440, March 2009,
               <https://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,
               <https://www.rfc-editor.org/info/rfc5441>.

   [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,
               <https://www.rfc-editor.org/info/rfc5520>.

   [RFC5553]   Farrel, A., Ed., Bradford, R., and JP. Vasseur, "Resource
               Reservation Protocol (RSVP) Extensions for Path Key
               Support", RFC 5553, DOI 10.17487/RFC5553, May 2009,
               <https://www.rfc-editor.org/info/rfc5553>.

   [RFC6006]   Zhao, Q., Ed., King, D., Ed., Verhaeghe, F., Takeda, T.,
               Ali, Z., and J. Meuric, "Extensions to the Path



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               Computation Element Communication Protocol (PCEP) for
               Point-to-Multipoint Traffic Engineering Label Switched
               Paths", RFC 6006, DOI 10.17487/RFC6006, September 2010,
               <https://www.rfc-editor.org/info/rfc6006>.

   [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,
               <https://www.rfc-editor.org/info/rfc6805>.

   [G-7715]    ITU-T, "ITU-T Recommendation G.7715 (2002), Architecture
               and Requirements for the Automatically Switched Optical
               Network (ASON).".

   [G-7715-2]  ITU-T, "ITU-T Recommendation G.7715.2 (2007), ASON
               routing architecture and requirements for remote route
               query.".

   [G-8080]    ITU-T, "ITU-T Recommendation G.8080/Y.1304, Architecture
               for the automatically switched optical network (ASON).".

Authors' Addresses

   Huaimo Chen
   Huawei Technologies
   Boston, MA
   USA

   EMail: huaimo.chen@huawei.com


   Dhruv Dhody
   Huawei Technologies
   Leela Palace
   Bangalore, Karnataka  560008
   INDIA

   EMail: dhruv.dhody@huawei.com












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