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Network Working Group                                            J. Dong
Internet-Draft                                                   M. Chen
Intended status: Standards Track                                D. Dhody
Expires: March 4, 2016                               Huawei Technologies
                                                             J. Tantsura
                                                                Ericsson
                                                       September 1, 2015


      BGP Extensions for Path Computation Element (PCE) Discovery
                 draft-dong-pce-discovery-proto-bgp-03

Abstract

   In networks where Path Computation Element (PCE) is used for
   centralized path computation, it is desirable for 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.  This
   document specifies the BGP extensions for PCE discovery in these
   scenarios.  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
   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 March 4, 2016.




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Copyright Notice

   Copyright (c) 2015 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
   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 . . . . . . . . . . . . . . . . . . . . .   7
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     7.2.  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 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).  Those IGP based mechanisms may not work in several
   scenarios where the PCEs do not participate in the IGP, and it is
   difficult for PCEs to participate in multiple IGP domains where PCE
   discovery is needed.

   In some scenarios, Backward Recursive Path Computation (BRPC)
   [RFC5441] can be used by cooperating PCEs to compute inter-domain
   path, in which case these cooperating PCEs should be known to each
   other in advance.  In case of inter-AS networks where the PCEs do not
   participate in a common IGP, the existing IGP discovery mechanism
   cannot be used to discover the PCEs in other domains.



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   In the Hierarchical PCE scenario [RFC6805], the child PCEs need to
   know the address of the parent PCEs.  This cannot be achieved through
   IGP based discovery, as normally the child PCEs and the parent PCE
   are under different administration and reside in different domains.

   Besides, as BGP could be used for north-bound distribution of routing
   and Label Switched Path (LSP) information to PCE as described in
   [I-D.ietf-idr-ls-distribution] [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, some other PCE
   discovery mechanism is needed.

   A detailed set of requirements for a PCE discovery mechanism are
   provided in [RFC4674].

   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 reuse the existing BGP sessions and mechanisms to achieve PCE
   discovery.  It should be noted that in each IGP domain, the IGP based
   PCE discovery mechanism may be used in conjunction with the BGP based
   PCE discovery.  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   |             |           |
       +-----------+       +-----------+             +-----------+
                                                            |
                                                            |   via
                                                            |   IGP
                                                            v
                                                      +-----------+
                                                      |    PCC    |
                                                      +-----------+


                      Figure 1: BGP for PCE discovery

   As shown in the network architecture in Figure 1, BGP is used for
   both routing information distribution and 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 between different PCEs.  The PCCs maybe co-
   located with the BGP speakers as shown in Figure 1.  The IGP based
   PCE discovery mechanism may be used for the distribution of PCE
   discovery information in IGP domain.

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 [I-D.ietf-idr-ls-distribution] are re-
   used, and a new NLRI Type is defined for PCE discovery information as
   below:




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   o  Type = TBD: PCE Discovery NLRI

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

       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 a new value which indicates
   the information source protocol is PCE.

              +-------------+----------------------------------+
              | Protocol-ID | NLRI information source protocol |
              +-------------+----------------------------------+
              |    TBD      |       PCE                        |
              +-------------+----------------------------------+

   As defined in [I-D.ietf-idr-ls-distribution], 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 [I-D.ietf-idr-ls-distribution] 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:











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

     Type |  Length    |      Name
    ------+------------+--------------------------------
     TBD  |     3      |  PATH-SCOPE sub-TLV
     TBD  |  variable  |  PCE-CAP-FLAGS sub-TLV
     TBD  |  variable  |  OSPF-PCE-DOMAIN sub-TLV
     TBD  |  variable  |  IS-IS-PCE-DOMAIN sub-TLV
     TBD  |  variable  |  OSPF-NEIG-PCE-DOMAIN sub-TLV
     TBD  |  variable  |  IS-IS-NEIG-PCE-DOMAIN sub-TLV


   More PCE Discovery sub-TLVs may be defined in future and the format
   SHOULD be in line with the new sub-TLVs defined for 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 the
   PCE selection on the PCCs would be based on the information carried
   in the PCE Discovery TLV.

   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.






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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 Protocol-ID for "PCE" from the "BGP-LS
   Protocol-IDs" 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.

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.  Acknowledgements

   The authors would like to thank Zhenbin Li and Hannes Gredler for
   their discussion and comments.

7.  References

7.1.  Normative References

   [I-D.ietf-idr-ls-distribution]
              Gredler, H., Medved, J., Previdi, S., Farrel, A., and S.
              Ray, "North-Bound Distribution of Link-State and TE
              Information using BGP", draft-ietf-idr-ls-distribution-11
              (work in progress), June 2015.

   [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>.




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   [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>.

   [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>.

7.2.  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-03 (work in progress), May 2015.

   [I-D.ietf-idr-te-pm-bgp]
              Wu, Q., Previdi, S., Gredler, H., Ray, S., and J.
              Tantsura, "BGP attribute for North-Bound Distribution of
              Traffic Engineering (TE) performance Metrics", draft-ietf-
              idr-te-pm-bgp-02 (work in progress), January 2015.

   [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>.








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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
   Leela Palace
   Bangalore, Karnataka  560008
   India

   Email: dhruv.ietf@gmail.com


   Jeff Tantsura
   Ericsson
   300 Holger Way
   San Jose, CA  95134
   US

   Email: jeff.tantsura@ericsson.com



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