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Internet Engineering Task Force                                  H. Chen
Internet-Draft                                       Huawei Technologies
Intended status: Standards Track                          April 30, 2018
Expires: November 1, 2018


  Extensions to Path Computation Element Communication Protocol (PCEP)
    for Backup Ingress of a Traffic Engineering Label Switched Path
              draft-chen-pce-compute-backup-ingress-13.txt

Abstract

   This document presents extensions to the Path Computation Element
   Communication Protocol (PCEP) for a PCC to send a request for
   computing a backup ingress for an MPLS TE P2MP LSP or an MPLS TE P2P
   LSP to a PCE and for a PCE to compute the backup ingress and reply to
   the PCC with a computation result for the backup ingress.

Status of this Memo

   This Internet-Draft is submitted to IETF 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
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on November 1, 2018.

Copyright Notice

   Copyright (c) 2018 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
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as



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   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Conventions Used in This Document  . . . . . . . . . . . . . .  4
   4.  Extensions to PCEP . . . . . . . . . . . . . . . . . . . . . .  4
     4.1.  Backup Ingress Capability Advertisement  . . . . . . . . .  4
       4.1.1.  Capability TLV in Existing PCE Discovery Protocol  . .  4
       4.1.2.  Open Message Extension . . . . . . . . . . . . . . . .  6
     4.2.  Request and Reply Message Extension  . . . . . . . . . . .  6
       4.2.1.  RP Object Extension  . . . . . . . . . . . . . . . . .  6
       4.2.2.  External Source Node . . . . . . . . . . . . . . . . .  7
       4.2.3.  Constraints between Ingress and Backup Ingress . . . .  8
       4.2.4.  Constraints for Backup Path  . . . . . . . . . . . . .  8
       4.2.5.  Backup Ingress Node  . . . . . . . . . . . . . . . . .  9
       4.2.6.  Backup Ingress PCEP Error Objects and Types  . . . . .  9
       4.2.7.  Request Message Format . . . . . . . . . . . . . . . .  9
       4.2.8.  Reply Message Format . . . . . . . . . . . . . . . . .  9
   5.  Security  Considerations . . . . . . . . . . . . . . . . . . . 10
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
     6.1.  Backup Ingress Capability Flag . . . . . . . . . . . . . . 10
     6.2.  Backup Ingress Capability TLV  . . . . . . . . . . . . . . 11
     6.3.  Request Parameter Bit Flags  . . . . . . . . . . . . . . . 11
     6.4.  PCEP Objects . . . . . . . . . . . . . . . . . . . . . . . 11
   7.  Acknowledgement  . . . . . . . . . . . . . . . . . . . . . . . 11
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 12
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 12
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 13



















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1.  Introduction

   RFC4090 "Fast Reroute Extensions to RSVP-TE for LSP Tunnels"
   describes two methods to protect P2P LSP tunnels or paths at local
   repair points.  The local repair points may comprise a number of
   intermediate nodes between an ingress node and an egress node along
   the path.  The first method is a one-to-one backup method, where a
   detour backup P2P LSP for each protected P2P LSP is created at each
   potential point of local repair.  The second method is a facility
   bypass backup protection method, where a bypass backup P2P LSP tunnel
   is created using MPLS label stacking to protect a potential failure
   point for a set of P2P LSP tunnels.  The bypass backup tunnel can
   protect a set of P2P LSPs that have similar backup constraints.

   RFC4875 "Extensions to RSVP-TE for P2MP TE LSPs" describes how to use
   the one-to-one backup method and facility bypass backup method to
   protect a link or intermediate node failure on the path of a P2MP
   LSP.

   However, there is no mention of locally protecting an ingress node
   failure in a protected P2MP LSP or P2P LSP.

   The methods for protecting an ingress node of a P2MP LSP or P2P LSP
   may be classified into two categories.

   A first category uses a backup P2MP LSP that is from a backup ingress
   node to the number of destination nodes for the P2MP LSP, and a
   backup P2P LSP that is from a backup ingress node to the destination
   node for the P2P LSP.  The disadvantages of this class of methods
   include more network resource such as computer power and link
   bandwidth consumption since the backup P2MP LSP or P2P LSP is from
   the backup ingress node to the number of destination nodes or the
   destination respectively.

   A second category uses a local P2MP LSP or P2P LSP for protecting the
   ingress of a P2MP LSP or P2P LSP locally.  The local P2MP LSP is from
   a backup ingress node to the next hop nodes of the ingress of the
   P2MP LSP.  The local P2P LSP is from a backup ingress node to the
   next hop node of the ingress of the P2P LSP.  It is desirable to let
   PCE compute these backup ingress nodes.

   This document defines extensions to the Path Computation Element
   Communication Protocol (PCEP) for a PCC to send a request for
   computing a backup ingress node for an MPLS TE P2MP LSP or an MPLS TE
   P2P LSP to a PCE and for a PCE to compute the backup ingress node and
   reply to the PCC with a computation result for the backup ingress
   node.




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2.  Terminology

   This document uses terminologies defined in RFC5440, RFC4090, and
   RFC4875.


3.  Conventions Used in This Document

   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.


4.  Extensions to PCEP

   This section describes the extensions to PCEP for computing a backup
   ingress of an MPLS TE P2MP LSP and an MPLS TE P2P LSP.

4.1.  Backup Ingress Capability Advertisement

4.1.1.  Capability TLV in Existing PCE Discovery Protocol

   There are a couple of options for advertising a PCE capability for
   computing a backup ingress for an MPLS TE P2MP LSP or an MPLS TE P2P
   LSP.

   The first option is to define a new flag in the OSPF and ISIS PCE
   Capability Flags to indicate the capability that a PCE is capable to
   compute both a backup ingress for an MPLS TE P2MP LSP and a backup
   ingress for an MPLS TE P2P LSP.

   The second option is to define two new flags.  One new flag in the
   OSPF and ISIS PCE Capability Flags indicates the capability that a
   PCE is capable to compute a backup ingress for an MPLS TE P2MP LSP;
   and another new flag in the OSPF and ISIS PCE Capability Flags
   indicates the capability that a PCE is capable to compute a backup
   ingress for an MPLS TE P2P LSP.

   This second option is preferred now.

   The format of the PCE-CAP-FLAGS sub-TLV is as follows:










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        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              Type = 5         |             Length            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       ~                 PCE Capability Flags                          ~
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         Type:     5
         Length:   Multiple of 4 octets
         Value:    This contains an array of units of 32-bit flags
                   numbered from the most significant as bit zero, where
                   each bit represents one PCE capability.

   The following capability bits have been assigned by IANA:

         Bit       Capabilities
          0        Path computation with GMPLS link constraints
          1        Bidirectional path computation
          2        Diverse path computation
          3        Load-balanced path computation
          4        Synchronized path computation
          5        Support for multiple objective functions
          6        Support for additive path constraints
                   (max hop count, etc.)
          7        Support for request prioritization
          8        Support for multiple requests per message
          9        Global Concurrent Optimization (GCO)
          10       P2MP path computation
         11-31     Reserved for future assignments by IANA.


   Reserved bits SHOULD be set to zero on transmission and MUST be
   ignored on receipt.

   For the second option, one bit such as bit 11 may be assigned to
   indicate that a PCE is capable to compute a backup ingress for an
   MPLS TE P2MP LSP and another bit such as bit 12 may be assigned to
   indicate that a PCE is capable to compute a backup ingress for an
   MPLS TE P2P LSP.

         Bit       Capabilities
          11       Backup ingress computation for P2MP LSP
          12       Backup ingress computation for P2P LSP
         13-31     Reserved for future assignments by IANA.





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4.1.2.  Open Message Extension

   If a PCE does not advertise its backup ingress compution capability
   during discovery, PCEP should be used to allow a PCC to discover,
   during the Open Message Exchange, which PCEs are capable of
   supporting backup ingress computation.

   To achieve this, we extend the PCEP OPEN object by defining a new
   optional TLV to indicate the PCE's capability to perform backup
   ingress compution for an MPLS TE P2MP LSP and an MPLS TE P2P LSP.

   We request IANA to allocate a value such as 8 from the "PCEP TLV Type
   Indicators" subregistry, as documented in Section below ("Backup
   Ingress Capability TLV").  The description is "backup ingress
   capable", and the length value is 2 bytes.  The value field is set to
   indicate the capability of a PCE for backup ingress compution for an
   MPLS TE LSP in details.

   We can use flag bits in the value field in the same way as the PCE
   Capability Flags described in the previous section.

   The inclusion of this TLV in an OPEN object indicates that the sender
   can perform backup ingress compution for an MPLS TE P2MP LSP or an
   MPLS TE P2P LSP.

   The capability TLV is meaningful only for a PCE, so it will typically
   appear only in one of the two Open messages during PCE session
   establishment.  However, in case of PCE cooperation (e.g., inter-
   domain), when a PCE behaving as a PCC initiates a PCE session it
   SHOULD also indicate its path computation capabilities.

4.2.  Request and Reply Message Extension

   This section describes extensions to the existing RP (Request
   Parameters) object to allow a PCC to request a PCE for computing a
   backup ingress of an MPLS TE P2MP LSP or an MPLS TE P2P LSP when the
   PCE receives the PCEP request.

4.2.1.  RP Object Extension

   The following flags are added into the RP Object:

   The I bit is added in the flag bits field of the RP object to tell
   the receiver of the message that the request/reply is for computing a
   bcakup ingress of an MPLS TE P2MP LSP and an MPLS TE P2P LSP.






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       o I ( Backup Ingress bit - 1 bit):
           0: This indicates that this is not PCReq/PCRep
              for backup ingress.
           1: This indicates that this is PCReq or PCRep message
              for backup ingress.


   The IANA request is referenced in Section below (Request Parameter
   Bit Flags) of this document.

   This I bit with the N bit defined in RFC6006 can indicate whether the
   request/reply is for a bcakup ingress of an MPLS TE P2MP LSP or an
   MPLS TE P2P LSP.

       o I = 1 and N = 1: This indicates that this is a PCReq/PCRep
                          message for backup ingress of an MPLS TE
                          P2MP LSP.
       o I = 1 and N = 0: This indicates that this is a PCReq/PCRep
                          message for backup ingress of an MPLS TE
                          P2P LSP.


4.2.2.  External Source Node

   In addition to the information about the path that an MPLS TE P2MP
   LSP or an MPLS TE P2P LSP traverses, a request message may comprise
   other information that may be used for computing the backup ingress
   for the P2MP LSP or P2P LSP.  For example, the information about an
   external source node, from which data traffic is delivered to the
   ingress node of the P2MP LSP or P2P LSP and transported to the egress
   node(s) via the P2MP LSP or P2P LSP, is useful for computing a backup
   ingress node.

   The PCC can specify an external source node (ESN) Object.  The ESN
   Object has the same format as the IRO object defined in [RFC5440]
   except that it only supports IPv4 and IPv6 prefix sub-objects.

   The object can only be carried in a PCReq message.  A Path Request
   may carry at most one external source node Object.

   The Object-Class and Object-types will need to be allocated by IANA.
   The IANA request is documented in Section below.  (PCEP Objects).

   Alternatively, we may use END-POINTS to represent an external source
   node in a request message for computing a backup ingress node of MPLS
   LSP.

   To represent an external source node efficiently, we define a new



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   type of END-POINTS objects for computing a backup ingress node of
   MPLS LSP.  The format of the new END-POINTS object body for IPv4
   (Object-Type 3) is 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                  External Source Type (11)                    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                 External Source IPv4 address                  |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   The new type of END-POINTS is External Source Node Type (11).  The
   final value for the type will be assigned by IANA.  This new type of
   END-POINTS object contains an external source node IPv4 address.

4.2.3.  Constraints between Ingress and Backup Ingress

   A request message sent to a PCE from a PCC for computing a backup
   ingress of an MPLS TE P2MP LSP or an MPLS TE P2P LSP may comprise a
   constraint indicating that there must be a path from the backup
   ingress node to be computed to the ingress node of the P2MP LSP or
   P2P LSP and that the length of the path is within a given hop limit
   such as one hop.

   This constraint can be considered as default by a PCE or explicitly
   sent to the PCE by a PCC [TBD].

4.2.4.  Constraints for Backup Path

   A request message sent to a PCE from a PCC for computing a backup
   ingress of a P2MP LSP or P2P LSP may comprise a constraint indicating
   that the backup ingress node to be computed may not be a node on the
   P2MP LSP or P2P LSP.  In addition, the request message may comprise a
   list of nodes, each of which is a candidate for the backup ingress
   node.

   A request message sent to a PCE from a PCC for computing a backup
   ingress of a P2MP LSP or P2P LSP may comprise a constraint indicating
   that there must be a path from the backup ingress node to be computed
   to the next-hop nodes of the ingress node of the P2MP LSP or P2P LSP
   and that there is not an internal node of the path from the backup
   ingress to the next-hop nodes on the P2MP LSP or P2P LSP .

   Most of these constraints for the backup path can be considered as
   default by a PCE.  The constraints for the backup path may be
   explicitly sent to the PCE by a PCC [TBD].



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4.2.5.  Backup Ingress Node

   The PCE may send a reply message to the PCC in return to the request
   message for computing a new backup ingress node.  The reply message
   may comprise information about the computed backup ingress node,
   which is contained in the path from the backup ingress computed to
   the next-hop node(s) of the ingress node of the P2MP LSP or P2P LSP.

   The backup ingress node is the root or head node of the backup path
   computed.

4.2.6.  Backup Ingress PCEP Error Objects and Types

   In some cases, the PCE may not complete the backup ingress
   computation as requested, for example based on a set of constraints.
   As such, the PCE may send a reply message to the PCC that indicates
   an unsuccessful backup ingress computation attempt.  The reply
   message may comprise a PCEP-error object, which may comprise an
   error-value, error-type and some detail information.

4.2.7.  Request Message Format

   The PCReq message is encoded as follows using RBNF as defined in
   [RFC5511].

   Below is the message format for a request message:

               <PCReq Message>::= <Common Header>
                                  [<svec-list>]
                                  <request>
               <request>::= <RP> <end-point-rro-pair-list> [<OF>]
                            [<LSPA>] [<BANDWIDTH>] [<metric-list>]
                            [<ESNO>]
                            [<IRO>]
                            [<LOAD-BALANCING>]
          where:
                <ESNO> is an external source node object.


   The definitions for svec-list, RP, end-point-rro-pair-list, OF, LSPA,
   BANDWIDTH, metric-list, IRO, and LOAD-BALANCING are described in
   RFC5440 and RFC6006.

4.2.8.  Reply Message Format

   The PCRep message is encoded as follows using RBNF as defined in
   [RFC5511].




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   Below is the message format for a reply message:

               <PCRep Message>::= <Common Header>
                                  <response>
               <response>::= <RP> <end-point-path-pair-list>
                             [<NO-PATH>]
                             [<attribute-list>]
        where:
              <end-point-path-pair-list>::=
                      [<END-POINTS>]<path>[<end-point-path-pair-list>]

              <path> ::= (<ERO>|<SERO>) [<path>]

              <attribute-list>::= [<OF>] [<LSPA>] [<BANDWIDTH>]
                                  [<metric-list>] [<IRO>]


   The definitions for RP, NO-PATH, END-POINTS, OF, LSPA, BANDWIDTH,
   metric-list, IRO, and SERO are described in RFC5440, RFC6006 and
   RFC4875.


5.  Security  Considerations

   The mechanism described in this document does not raise any new
   security issues for the PCEP, OSPF and IS-IS protocols.


6.  IANA Considerations

   This section specifies requests for IANA allocation.

6.1.  Backup Ingress Capability Flag

   Two new OSPF Capability Flags are defined in this document to
   indicate the capabilities for computing a backup ingress for an MPLS
   TE P2MP LSP and an MPLS TE P2P LSP.  IANA is requested to make the
   assignment from the "OSPF Parameters Path Computation Element (PCE)
   Capability Flags" registry:

         Bit       Description                         Reference
          11       Backup ingress for P2MP LSP         This I-D
          12       Backup ingress for P2P LSP          This I-D








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6.2.  Backup Ingress Capability TLV

   A new backup ingress capability TLV is defined in this document to
   allow a PCE to advertize its backup ingress computation capability.
   IANA is requested to make the following allocation from the "PCEP TLV
   Type Indicators" sub-registry.

         Value       Description                      Reference
          8          Backup ingress capable           This I-D



6.3.  Request Parameter Bit Flags

   A new RP Object Flag has been defined in this document.  IANA is
   requested to make the following allocation from the "PCEP RP Object
   Flag Field" Sub-Registry:

         Bit       Description                         Reference
          16       Backup ingress (I-bit)              This I-D



6.4.  PCEP Objects

   An External Source Node Object-Type is defined in this document.
   IANA is requested to make the following Object-Type allocation from
   the "PCEP Objects" sub-registry:

           Object-Class Value     33
           Name                   External Source Node
           Object-Type            1: IPv4
                                  2: IPv6
                                  3-15: Unassigned
           Reference              This I-D




7.  Acknowledgement

   The author would like to thank Cyril Margaria, Ramon Casellas, Dhruv
   Dhody and Quintin Zhao for their valuable comments and suggestions on
   this draft.


8.  References




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8.1.  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>.

   [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>.

   [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>.

   [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>.

   [RFC4875]  Aggarwal, R., Ed., Papadimitriou, D., Ed., and S.
              Yasukawa, Ed., "Extensions to Resource Reservation
              Protocol - Traffic Engineering (RSVP-TE) for Point-to-
              Multipoint TE Label Switched Paths (LSPs)", RFC 4875,
              DOI 10.17487/RFC4875, May 2007,
              <https://www.rfc-editor.org/info/rfc4875>.

   [RFC6006]  Zhao, Q., Ed., King, D., Ed., Verhaeghe, F., Takeda, T.,
              Ali, Z., and J. Meuric, "Extensions to the Path
              Computation Element Communication Protocol (PCEP) for
              Point-to-Multipoint Traffic Engineering Label Switched
              Paths", RFC 6006, DOI 10.17487/RFC6006, September 2010,
              <https://www.rfc-editor.org/info/rfc6006>.

8.2.  Informative References

   [RFC4655]  Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
              Element (PCE)-Based Architecture", RFC 4655, DOI 10.17487/
              RFC4655, August 2006,
              <https://www.rfc-editor.org/info/rfc4655>.

   [RFC5862]  Yasukawa, S. and A. Farrel, "Path Computation Clients
              (PCC) - Path Computation Element (PCE) Requirements for
              Point-to-Multipoint MPLS-TE", RFC 5862, DOI 10.17487/
              RFC5862, June 2010,
              <https://www.rfc-editor.org/info/rfc5862>.



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Author's Address

   Huaimo Chen
   Huawei Technologies
   Boston, MA
   USA

   Email: Huaimo.chen@huawei.com











































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