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Network Working Group                                            J. Dong
Internet-Draft                                                   M. Chen
Intended status: Standards Track                                D. Dhody
Expires: December 26, 2016                           Huawei Technologies
                                                             J. Tantsura
                                                              Individual
                                                               K. Kumaki
                                                        KDDI Corporation
                                                                T. Murai
                                         Furukawa Network Solution Corp.
                                                           June 24, 2016


      BGP Extensions for Path Computation Element (PCE) Discovery
                 draft-dong-pce-discovery-proto-bgp-05

Abstract

   In networks where Path Computation Element (PCE) is used for
   centralized path computation, it is desirable for the Path
   Computation Clients (PCCs) to automatically discover a set of PCEs
   and select the suitable ones to establish the PCEP session.  RFC 5088
   and RFC 5089 define the PCE discovery mechanisms based on Interior
   Gateway Protocols (IGP).  This document describes several scenarios
   in which the IGP based PCE discovery mechanisms cannot be used
   directly.  In such scenarios, BGP might be suitable, thus this
   document specifies the BGP extensions for PCE discovery.  The BGP
   based PCE discovery mechanism is complementary to the existing IGP
   based mechanisms.

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 RFC 2119 [RFC2119].

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



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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 December 26, 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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Carrying PCE Discovery Information in BGP . . . . . . . . . .   4
     2.1.  PCE Address Information . . . . . . . . . . . . . . . . .   4
     2.2.  PCE Discovery TLVs  . . . . . . . . . . . . . . . . . . .   5
   3.  Operational Considerations  . . . . . . . . . . . . . . . . .   6
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   6.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   7
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   In network scenarios where Path Computation Element (PCE) is used for
   centralized path computation, it is desirable for the Path
   Computation Clients (PCCs) to automatically discover a set of PCEs
   and select the suitable ones to establish the PCEP session.
   [RFC5088] and [RFC5089] define the PCE discovery mechanisms based on
   Interior Gateway Protocols (IGP).

   The IGP based discovery mechanism requires the PCE participate in the
   IGP network, which usually requires that the PCE is directly adjacent
   to at least one of the IGP routers in the network.  In some scenarios



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   such requirement cannot be satisfied.  For example, a PCE may need to
   provide path computation service to some subsidiary networks of an
   operator, which typically locate in different geographical region
   (and not IGP adjacent).  Also when PCE function is implemented in a
   central server running IGP on individual interfaces to each IGP area
   can be cumbersome.

   The requirement on PCE discovery, as described in [RFC4674], also
   include the automatic discovery of the PCEs in other domains, as it
   is a desirable function in the case of inter-domain path computation.
   The IGP based discovery mechanisms cannot meet such requirement.

   For example, Backward Recursive Path Computation (BRPC) [RFC5441] can
   be used by cooperating PCEs to compute an inter-AS path, in which
   case these cooperating PCEs should be known to each other in advance.
   In this case the PCEs belongs to different AS and do not participate
   in a common IGP, the IGP based discovery mechanisms are not
   applicable.

   Another example is the hierarchical PCE scenario [RFC6805], in which
   the child PCEs need to know the information of the parent PCEs.  This
   cannot be achieved via IGP based discovery, as the child PCEs and the
   parent PCE are usually in different domains.

   In some BGP IP-VPN networks, an end-to-end TE LSP between the CEs
   (Customer Edges) of a particular VPN is required [RFC5824].  In this
   case, CEs need the information of the PCE which can perform the CE to
   CE path computation for that VPN.  Since the PCE may locate in a VPN
   site different from the site of the requesting CE, the IGP based
   discovery mechanism is not directly applicable, and some BGP based
   discovery mechanism is required to distribute the per-VPN PCE
   information to the VPN sites.

   Since BGP has been extended for north-bound distribution of routing
   and Label Switched Path (LSP) information to PCE [RFC7752]
   [I-D.ietf-idr-te-lsp-distribution] and [I-D.ietf-idr-te-pm-bgp], PCEs
   can obtain the routing information without participating in IGP.  In
   this scenario, a new BGP based PCE discovery mechanism is needed.

   This document proposes to extend BGP for PCE discovery in the above
   scenarios.  In networks where BGP-LS is used for the north-bound
   routing information distribution to PCE, the BGP based PCE discovery
   can make use of the existing BGP sessions and mechanisms to achieve
   automatic PCE discovery.  Further IGP may be used to redistribute
   remote PCE information, the detailed mechanism is out of the scope of
   this document.  Thus the BGP based PCE discovery is complementary to
   the existing IGP based mechanisms.




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                           +-----------+
                           |    PCE    |
                           +-----------+
                                 |
                                 v
                           +-----------+
                           |    BGP    |               +-----------+
                           |  Speaker  |               |    PCE    |
                           +-----------+               +-----------+
                             |   |   |                       |
                             |   |   |                       |
             +---------------+   |   +-------------------+   |
             v                   v                       v   v
       +-----------+       +-----------+             +-----------+
       |    BGP    |       |    BGP    |             |    BGP    |
       |  Speaker  |       |  Speaker  |    . . .    |  Speaker  |
       |   & PCC   |       |   & PCC   |             |   & PCC   |
       +-----------+       +-----------+             +-----------+


                      Figure 1: BGP for PCE discovery

   As shown in the network architecture in Figure 1, BGP is used both
   for routing information distribution and for PCE information
   discovery.  The routing information is collected from the network
   elements and distributed to PCE, while the PCE discovery information
   is advertised from PCE to PCCs, or among different PCEs.  The PCCs
   maybe co-located with the BGP speakers as shown in Figure 1.

2.  Carrying PCE Discovery Information in BGP

2.1.  PCE Address Information

   The PCE discovery information is advertised in BGP UPDATE messages
   using the MP_REACH_NLRI and MP_UNREACH_NLRI attributes [RFC4760].
   The AFI and SAFI defined in [RFC7752] are re-used.  For the PCEs in
   public network, the AFI / SAFI pair is 16388 / 71, while for the PCEs
   of a particular VPN, the AFI / SAFI pair is set to 16388 / 72.

   A new NLRI Type is defined for PCE discovery information as below:

   o  Type = TBD: PCE Discovery NLRI

   The format of PCE Discovery NLRI is shown in the following figure:







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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
      +-+-+-+-+-+-+-+-+
      |  Protocol-ID  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           Identifier                          |
      |                            (64 bits)                          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                  PCE-Address (4 or 16 octets)                 ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                       Figure 2. PCE Discovery NLRI

   The 'Protocol-ID' field SHOULD be set to the appropriate value which
   indicates the source of the PCE discovery information.  If BGP
   speaker and PCE are co-located, the Protocol-ID SHOULD be set to
   "Direct".  In other cases, it is RECOMMENDED that the Protocol-ID
   value be set to "Static configuration".

   As defined in [RFC7752], the 64-Bit 'Identifier' field is used to
   identify the "routing universe" where the PCE belongs.

2.2.  PCE Discovery TLVs

   The detailed PCE discovery information is carried in the BGP-LS
   attribute [RFC7752] with a new "PCE Discovery TLV", which contains a
   set of sub-TLVs for specific PCE discovery information.  The PCE
   Discovery TLV and sub-TLVs SHOULD only be used with the PCE Discovery
   NLRI.

   The format of the PCE Discovery TLV is shown as below:

      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             |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     ~                 PCE Discovery Sub-TLVs (variable)             ~
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                       Figure 3. PCE Discovery TLV

   The PCE Discovery sub-TLVs are listed as below.  The format of the
   PCE Discovery sub-TLVs are consistent with the IGP PCED sub-TLVs as
   defined in [RFC5088] and [RFC5089].  The PATH-SCOPE sub-TLV MUST
   always be carried in the PCE Discovery TLV.  Other PCE Discovery sub-



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   TLVs are optional and may facilitate the PCE selection process on the
   PCCs.

     Type |  Length    |      Name
    ------+------------+--------------------------------
     1    |     3      |  PATH-SCOPE sub-TLV
     2    |  variable  |  PCE-CAP-FLAGS sub-TLV
     3    |  variable  |  OSPF-PCE-DOMAIN sub-TLV
     4    |  variable  |  IS-IS-PCE-DOMAIN sub-TLV
     5    |  variable  |  OSPF-NEIG-PCE-DOMAIN sub-TLV
     6    |  variable  |  IS-IS-NEIG-PCE-DOMAIN sub-TLV


   More PCE Discovery sub-TLVs may be defined in future.  The format and
   semantic of new PCE Discovery sub-TLVs SHOULD be consistent in BGP
   and IGP based PCE discovery.

3.  Operational Considerations

   Existing BGP operational procedures apply to the advertisement of PCE
   discovery information.  This information is treated as pure
   application level data which has no immediate impact on forwarding
   states.  Normal BGP path selection can be applied to PCE Discovery
   NLRI only for the information propagation in the network, while on
   PCCs the PCE selection is based on the information carried in the PCE
   Discovery TLV.  The PCE discovery information SHOULD be advertised
   only to the domains where such information is allowed to be used.
   This can be achieved by policy control on the ASBRs.

   The PCE discovery information is considered relatively stable and
   does not change frequently, thus this information will not bring
   significant impact on the amount of BGP updates in the network.

4.  IANA Considerations

   IANA needs to assign a new NLRI Type for 'PCE Discovery NLRI' from
   the "BGP-LS NLRI-Types" registry.

   IANA needs to assign a new TLV code point for 'PCE Discovery TLV'
   from the "node anchor, link descriptor and link attribute TLVs"
   registry.

   IANA needs to create a new registry for "PCE Discovery Sub-TLVs".
   The registry will be initialized as shown in section 2.2 of this
   document.






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5.  Security Considerations

   Procedures and protocol extensions defined in this document do not
   affect the BGP security model.  See the 'Security Considerations'
   section of [RFC4271] for a discussion of BGP security.  Also refer to
   [RFC4272] and [RFC6952] for analysis of security issues for BGP.

6.  Contributors

   The following individuals gave significant contributions to this
   document:

   Takuya Miyasaka
   KDDI Corporation
   ta-miyasaka@kddi.com

7.  Acknowledgements

   The authors would like to thank Zhenbin Li, Hannes Gredler, Jan
   Medved, Adrian Farrel, Julien Meuric and Jonathan Hardwick for the
   valuable discussion and comments.

8.  References

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,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
              Border Gateway Protocol 4 (BGP-4)", RFC 4271,
              DOI 10.17487/RFC4271, January 2006,
              <http://www.rfc-editor.org/info/rfc4271>.

   [RFC4760]  Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
              "Multiprotocol Extensions for BGP-4", RFC 4760,
              DOI 10.17487/RFC4760, January 2007,
              <http://www.rfc-editor.org/info/rfc4760>.

   [RFC5088]  Le Roux, JL., Ed., Vasseur, JP., Ed., Ikejiri, Y., and R.
              Zhang, "OSPF Protocol Extensions for Path Computation
              Element (PCE) Discovery", RFC 5088, DOI 10.17487/RFC5088,
              January 2008, <http://www.rfc-editor.org/info/rfc5088>.






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   [RFC5089]  Le Roux, JL., Ed., Vasseur, JP., Ed., Ikejiri, Y., and R.
              Zhang, "IS-IS Protocol Extensions for Path Computation
              Element (PCE) Discovery", RFC 5089, DOI 10.17487/RFC5089,
              January 2008, <http://www.rfc-editor.org/info/rfc5089>.

   [RFC7752]  Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
              S. Ray, "North-Bound Distribution of Link-State and
              Traffic Engineering (TE) Information Using BGP", RFC 7752,
              DOI 10.17487/RFC7752, March 2016,
              <http://www.rfc-editor.org/info/rfc7752>.

8.2.  Informative References

   [I-D.ietf-idr-te-lsp-distribution]
              Dong, J., Chen, M., Gredler, H., Previdi, S., and J.
              Tantsura, "Distribution of MPLS Traffic Engineering (TE)
              LSP State using BGP", draft-ietf-idr-te-lsp-
              distribution-04 (work in progress), December 2015.

   [I-D.ietf-idr-te-pm-bgp]
              Previdi, S., Wu, Q., Gredler, H., Ray, S.,
              Tantsura, j., Filsfils, C., and L. Ginsberg,
              "BGP-LS Advertisement of IGP Traffic Engineering
              Performance Metric Extensions", draft-ietf-idr-te-pm-
              bgp-03 (work in progress), May 2016.

   [RFC4272]  Murphy, S., "BGP Security Vulnerabilities Analysis",
              RFC 4272, DOI 10.17487/RFC4272, January 2006,
              <http://www.rfc-editor.org/info/rfc4272>.

   [RFC4674]  Le Roux, J., Ed., "Requirements for Path Computation
              Element (PCE) Discovery", RFC 4674, DOI 10.17487/RFC4674,
              October 2006, <http://www.rfc-editor.org/info/rfc4674>.

   [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>.

   [RFC5824]  Kumaki, K., Ed., Zhang, R., and Y. Kamite, "Requirements
              for Supporting Customer Resource ReSerVation Protocol
              (RSVP) and RSVP Traffic Engineering (RSVP-TE) over a BGP/
              MPLS IP-VPN", RFC 5824, DOI 10.17487/RFC5824, April 2010,
              <http://www.rfc-editor.org/info/rfc5824>.





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   [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>.

   [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>.

Authors' Addresses

   Jie Dong
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Rd.
   Beijing  100095
   China

   Email: jie.dong@huawei.com


   Mach(Guoyi) Chen
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Rd.
   Beijing  100095
   China

   Email: mach.chen@huawei.com


   Dhruv Dhody
   Huawei Technologies
   Divyashree Techno Park, Whitefield
   Bangalore, Karnataka  560066
   India

   Email: dhruv.ietf@gmail.com


   Jeff Tantsura
   Individual
   US

   Email: jefftant.ietf@gmail.com





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   Kenji Kumaki
   KDDI Corporation
   Garden Air Tower, Iidabashi, Chiyoda-ku
   Tokyo  102-8460
   Japan

   Email: ke-kumaki@kddi.com


   Tomoki Murai
   Furukawa Network Solution Corp.
   5-1-9, Higashi-Yawata, Hiratsuka
   Kanagawa  254-0016
   Japan

   Email: murai@fnsc.co.jp



































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