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PCE Working Group                                                H. Chen
Internet-Draft                                       Huawei Technologies
Intended status: Standards Track                                  M. Toy
Expires: May 4, 2017
                                                                  L. Liu
                                                                 Fujitsu
                                                                   Z. Li
                                                            China Mobile
                                                        October 31, 2016


                       Hierarchical PCE Discovery
                     draft-chen-pce-h-discovery-01

Abstract

   This document presents extensions to the Path Computation Element
   Communication Protocol (PCEP) to discover parent child relations and
   the information on a parent and a child PCE in a hierarchical PCE
   system.

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
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   Drafts is at http://datatracker.ietf.org/drafts/current/.

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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 May 4, 2017.

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



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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Conventions Used in This Document  . . . . . . . . . . . . . .  4
   4.  Extensions to PCEP . . . . . . . . . . . . . . . . . . . . . .  4
     4.1.  Discovery of Parent Child Relation . . . . . . . . . . . .  4
     4.2.  Sub-TLVs . . . . . . . . . . . . . . . . . . . . . . . . .  5
       4.2.1.  Domain Sub-TLV . . . . . . . . . . . . . . . . . . . .  5
       4.2.2.  PCE ID Sub-TLV . . . . . . . . . . . . . . . . . . . .  6
     4.3.  Procedures . . . . . . . . . . . . . . . . . . . . . . . .  7
       4.3.1.  Configuration Driven Discovery . . . . . . . . . . . .  7
       4.3.2.  Auto Discovery . . . . . . . . . . . . . . . . . . . .  9
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
   7.  Acknowledgement  . . . . . . . . . . . . . . . . . . . . . . . 10
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 10
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 10



























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1.  Introduction

   A hierarchical PCE architecture is described in RFC 6805, in which a
   parent PCE has a number of child PCEs.  A child PCE may also be a
   parent PCE, which has multiple child PCEs.

   For a parent PCE, it needs to obtain the information about each of
   its child PCEs.  The information about a child PCE comprises the
   address or ID of the PCE and the domain for which the PCE is
   responsible.  It may also include the position of the PCE, which
   indicates whether the PCE is a leaf (i.e., only a child) or branch
   (i.e., a child and also a parent).  In addition, the information may
   indicate whether the child PCE and its responsible domain is in a
   same organization as the parent PCE.

   For a child PCE, it needs to obtain the information about its parent
   PCE, which includes the address or ID of the parent PCE.  The
   information may also indicate whether the parent PCE is in a same
   organization as the child PCE.

   After a user configures a parent PCE and a child PCE over a session,
   this parent-child PCE relation needs to be discovered in the protocol
   level.  This is similar to OSPF and BGP.  After an adjacency between
   two OSPF routers is configured by a user, the OSPF protocol will
   discover the adjacency and forms the OSPF adjacency after the
   discovery.  After a peer relation between two BGP routers is
   configured by a user, the BGP protocol will discover the peer and
   forms the BGP peer relation after the discovery.

   For a parent-child PCE relation discovery, the PCE protocol needs to
   check or confirm whether the parent-child PCE relation is OK (can be
   formed).  If so, the child PCE has to send its parent PCE the
   information about the child PCE and vice versa.

   This document presents extensions to the Path Computation Element
   Communication Protocol (PCEP) to discover parent child relations and
   the information on a parent and a child PCE in a hierarchical PCE
   system.

2.  Terminology

   The following terminology is used in this document.

   Parent Domain:  A domain higher up in a domain hierarchy such that it
      contains other domains (child domains) and potentially other links
      and nodes.





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   Child Domain:  A domain lower in a domain hierarchy such that it has
      a parent domain.

   Parent PCE:  A PCE responsible for selecting a path across a parent
      domain and any number of child domains by coordinating with child
      PCEs and examining a topology map that shows domain inter-
      connectivity.

   Child PCE:  A PCE responsible for computing the path across one or
      more specific (child) domains.  A child PCE maintains a
      relationship with at least one parent PCE.

   TED:  Traffic Engineering Database.

   This document uses terminology defined in [RFC5440].

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 to discover the
   relation between a parent PCE and a child PCE and the information on
   a parent and a child PCE in a hierarchical PCE system.  A child PCE
   is simply called a child and a parent PCE is called a parent in the
   following sections.

4.1.  Discovery of Parent Child Relation

   During a PCEP session establishment between two PCEP speakers, each
   of them advertises its capabilities for Hierarchical PCE (H-PCE for
   short) through the Open Message with the Open Object containing a new
   TLV to indicate its capabilities for H-PCE.  This new TLV is called
   H-PCE capability TLV.  It has the following format.

        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 = TBD1        |            Length             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |P|C|S|B|                Capability Flags                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                       Optional  Sub-TLVs                      |
       ~                                                               ~
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



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   The type of the TLV is TBD1.  It has a length of 4 octets plus the
   size of optional Sub-TLVs.  The value of the TLV comprises a
   capability flags field of 32 bits, which are numbered from the most
   significant as bit zero.  Some of them are defined as follows.  The
   others are not defined and MUST be set to zero.

   o  P (Parent - 1 bit): Bit 0 is used as P flag.  It is set to 1
      indicating a parent.

   o  C (Child - 1 bit): Bit 1 is used as C flag.  It is set to 1
      indicating a child.

   o  S (Same Org - 1 bit): Bit 2 is used as S flag.  It is set to 1
      indicating a PCE in a same organization as its remote peer.

   o  B (Both - 1 bit): Bit 3 is used as B flag.  It is set to 1
      indicating a PCE as both a child and a parent.

   The following Sub-TLVs are defined:

   o  A Domain Sub-TLV containing an AS number and optional area, and

   o  PCE-ID Sub-TLV containing the ID of a PCE.

4.2.  Sub-TLVs

   When a child sends its parent a Open message, it places the
   information about it in the message through using some optional Sub-
   TLVs.  When a parent sends each of its child PCEs a Open message, it
   puts the information about it in the message.

4.2.1.  Domain Sub-TLV

   A domain is a AS or an area in an AS.  An AS is identified by an AS
   number.  An area in an AS is identified by the combination of the AS
   and the area.  The former is indicated by an AS number and the latter
   by an area number.  A domain is represented by a domain Sub-TLV
   containing an AS number and a optional area number.

   The format of the domain Sub-TLV is shown 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 (tTBD1)          |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       AS Number (4 bytes)                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     ~                      Optional  Area Number                    ~
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   where Length is four plus size of area number.


   An AS is represented by a domain Sub-TLV containing only the AS
   number of the AS.  In this case, the Length is four.  An area in an
   AS is represented by a domain Sub-TLV containing the AS number of the
   AS and the area number of the area.  In this case, the Length is
   eight.

4.2.2.  PCE ID Sub-TLV

   An Identifier (ID) of a PCE (PCE ID for short) is a 32-bit number
   that can uniquely identify the PCE among all PCEs.  This 32-bit
   number for PCE ID SHOULD NOT be zero.

   The format of the PCE ID Sub-TLV is shown 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 (tTBD3)          |           Length (4)          |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                        PCE ID (4 bytes)                       |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The PCE ID Sub-TLV specifies an non zero number as the identifier of the PCE.

   Alternatively, an IP address attached to a PCE can also be used as an
   identifier of the PCE.  The format of an IPv4 address Sub-TLV is
   shown 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 (tTBD4)          |           Length (4)          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     IPv4 Address (4 bytes)                    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



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   The IPv4 address Sub-TLV specifies an IPv4 address associated with
   the PCE, which is used as the identifier of the PCE.

   The format of an IPv6 address Sub-TLV is shown 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 (tTBD5)          |          Length (16)          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     IPv6 Address (16 bytes)                   |
     ~                                                               ~
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   The IPv6 Sub-TLV specifies an IPv6 address associated with the PCE,
   which is used as the identifier of the PCE.

4.3.  Procedures

   There are two types of procedures for parent-child PCE relation
   discoveries: auto-discovery and configuration driven discovery.

   For two PCEs belonging to two different service providers, there are
   some security concerns for automatically discovering the parent-child
   PCE relation without any configuration.  For PCEs belonging to the
   same service provider, we can use auto-discovery for discovering the
   parent-child PCE relations.  This section considers these two types
   of discoveries.

4.3.1.  Configuration Driven Discovery

   For two PCEs A and B configured as parent and child, they discover
   each other through Open messages in the initialization phase.  The
   following is a sequence of events related.

             A                                     B
        Configure B                           Configure A
        as its child                          as its parent
                        Open (P=1, A's ID)
                       -------------------> Same as configured
                                              A is B's parent
                        Open (C=1, B's ID)
    Same as configured <-------------------
      B is A's child


   A sends B a Open message with P=1 and A's ID after B is configured as



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   its child on it.  B sends A a Open message with C=1 and B's ID after
   A is configured as its parent on it.

   When A receives the Open message from B and determines C=1 and the
   PCE ID of B in the message is the same as the PCE ID of the child
   locally configured, B is A's child.

   When B receives the Open message from A and determines P=1 and the
   PCE ID of A in the message is the same as the PCE ID of the parent
   locally configured, A is B's parent.

   The Open message from child B to its parent A contains B's domain,
   which is represented by a domain Sub-TLV in the H-PCE capability TLV.
   If child B is also a parent, the B flag in the TLV is set to 1.

   The PCE ID in a Open message may be represented in one of the
   following ways:

   o  The source IP address of the message (i.e., PCE session).

   o  A PCE ID Sub-TLV in the H-PCE capability TLV.

   o  An IP address Sub-TLV in the H-PCE capability TLV.

   When the IP address Sub-TLV is used, the address in the Sub-TLV MUST
   be the same as the source IP address of the PCE session.

   For a child that is a leaf, it is normally responsible for one
   domain, which is contained in the message to its parent.

   For a child that is a branch (i.e., also a parent of multiple child
   PCEs), it may be directly responsible for one domain, which is
   contained in the message to its parent.  In addition, it is
   responsible for the domains of its child PCEs.  In other words, it is
   responsible for computing paths crossing the domains through working
   together with its child PCEs.  If these domains are all areas of an
   AS, the AS is included in the message to its parent.

   A parent stores the information about each of its child PCEs
   received.  When the session to one of them is down, it removes the
   information about the child on that session.

   A child stores the information about its parent received.  When the
   session to the parent is down, it removes the information about the
   parent.

   If there already exists a session between A and B and the
   configurations on parent and child are issued on them, the procedures



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   above may be executed through bringing down the existing session and
   establishing a new session between them.  Alternatively, they may
   discover each other regarding to H-PCE through using extended
   Notification messages in the same procedures as using Open messages
   described above without bringing down the existing session.

   The following new Notification-type and Notification-value are
   defined for H-PCE:

   o  Notification-type=5 (TBD): Discovery of H-PCE

      *  Notification-value=1: The information about a parent PCE or a
         child PCE.  A Notification-type=5, Notification-value=1
         indicates that the PCE sends its peer the information about it
         and a TLV containing the information is in the Notification
         object.  The format and contents of the TLV is the same as the
         H-PCE capability TLV described above.  The only difference may
         be the type of the TLV.

4.3.2.  Auto Discovery

   For two PCEs A and B belonging to the same service provider, their
   parent-child PCE relation may be automatically discovered without any
   configuration or with minimum configuration.

   For a parent-child PCE relation between two PCEs A and B to be
   automatically discovered, two conditions need to be met.  One is that
   both A and B know that they are in the same service provider.  The
   other is that one of them determines that it is the parent or child.

   After these two conditions are met, A and B may automatically
   discover their parent-child relation through exchanging the messages
   in a way similar to the one described in the previous section.

   If A (or B) is a child of another PCE X over the session between X
   and A (or B), then it can determine that it is the parent over the
   session between A and B. After the parent is determined between A and
   B, the child is implied.

   If A (or B) is not any child of a PCE, then it can not determine
   whether it is a parent or child over the session between A and B. In
   this case, a configuration on A or B is needed to indicate the parent
   or child.

   Two PCEs A and B may know that they are in the same service provider
   through their domains.  In general, the areas in an AS belong to a
   same service provider.  After PCEs A and B know that they are
   responsible for the areas in the same AS, they know that they are in



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   the same service provider.

   For two PCEs A and B responsible for two different ASes, it is hard
   for them to determine whether they are in the same service provider.
   In this case, a configuration on A and B is needed to indicate they
   are in the same service provider.

5.  Security Considerations

   The mechanism described in this document does not raise any new
   security issues for the PCEP protocols.

6.  IANA Considerations

   This section specifies requests for IANA allocation.

7.  Acknowledgement

   The authors would like to thank people for their valuable comments on
   this draft.

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>.

   [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>.

   [RFC5440]  Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol (PCEP)", RFC 5440,
              DOI 10.17487/RFC5440, March 2009,
              <http://www.rfc-editor.org/info/rfc5440>.

8.2.  Informative References

   [RFC4105]  Le Roux, J., Ed., Vasseur, J., Ed., and J. Boyle, Ed.,
              "Requirements for Inter-Area MPLS Traffic Engineering",
              RFC 4105, DOI 10.17487/RFC4105, June 2005,
              <http://www.rfc-editor.org/info/rfc4105>.




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   [RFC4216]  Zhang, R., Ed. and J. Vasseur, Ed., "MPLS Inter-Autonomous
              System (AS) Traffic Engineering (TE) Requirements",
              RFC 4216, DOI 10.17487/RFC4216, November 2005,
              <http://www.rfc-editor.org/info/rfc4216>.

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

Authors' Addresses

   Huaimo Chen
   Huawei Technologies
   Boston, MA,
   USA

   EMail: Huaimo.chen@huawei.com


   Mehmet Toy
   USA

   EMail: mtoy054@yahoo.com


   Lei Liu
   Fujitsu
   USA

   EMail: lliu@us.fujitsu.com


   Zhenqiang Li
   China Mobile
   No.32 Xuanwumenxi Ave., Xicheng District
   Beijing  100032
   P.R. China

   EMail: li_zhenqiang@hotmail.com











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