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PCE WG                                                        Quan Xiong
Internet-Draft                                           Shuangping Zhan
Intended status: Standards Track                         ZTE Corporation
Expires: September 12, 2019                                   Fangwei Hu
                                                              Individual
                                                          March 11, 2019


                     PCEP extensions for SR-MPLS-TP
                draft-xiong-pce-pcep-extension-sr-tp-03

Abstract

   This document proposes a set of extensions to PCEP for Transport
   Profile of SR-MPLS (SR-MPLS-TP) networks and defines a mechanism to
   create the bi-directional SR tunnel with PCE.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on September 12, 2019.

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   Copyright (c) 2019 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  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   2
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  The SR-MPLS-TP Architecture with PCE  . . . . . . . . . . . .   3
     2.1.  SR Path SID Allocation  . . . . . . . . . . . . . . . . .   5
     2.2.  Associated Bi-directional SR tunnel . . . . . . . . . . .   6
   3.  PCEP extensions for SR-MPLS-TP  . . . . . . . . . . . . . . .   7
     3.1.  ERO extension . . . . . . . . . . . . . . . . . . . . . .   8
     3.2.  E bit in LSP object . . . . . . . . . . . . . . . . . . .   9
     3.3.  Processing Rules  . . . . . . . . . . . . . . . . . . . .   9
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   The Path Computation Element Communication Protocol (PCEP) defined in
   [RFC5440] provides mechanisms for Path Computation Elements (PCEs) to
   perform path computations in response to Path Computation Clients
   (PCCs) requests.

   [I-D.ietf-pce-segment-routing] proposes extensions to PCEP that allow
   a stateful PCE to compute Traffic Engineering (TE) paths in segment
   routing (SR) networks.  But it is applicable to Multi-protocol Label
   Switching (MPLS) networks refered as to SR-MPLS.  In the context of
   the Transport Profile of SR-MPLS, referred to in this document as SR-
   MPLS-TP, a Path Segment uniquely identifies an SR path in a specific
   context.  It is required to extend the PCEP protocol to meet the new
   requirements for SR-MPLS-TP services.  One of the requirements is the
   bidirectional SR tunnel described in
   [I-D.ietf-spring-mpls-path-segment].

   This document proposes a set of extensions to PCEP for SR-MPLS-TP
   networks and defines a mechanism to create the bidirectional SR
   tunnel with PCE.

1.1.  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].






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1.2.  Terminology

   The terminology is defined as [RFC5440],
   [I-D.ietf-pce-segment-routing] and
   [I-D.ietf-spring-mpls-path-segment].

   MPLS-TP: MPLS transport profile.

   SR: Segment Routing.

   SR-MPLS: Segment routing over MPLS data plane.

   SR-MPLS-TP: Transport Profile of SR-MPLS.

2.  The SR-MPLS-TP Architecture with PCE

   As described in [I-D.ietf-spring-mpls-path-segment], in transport
   networks, the centralized controller may calculate the end to end SR
   paths, and creates the ordered segment list.  The centralized
   controller may be replaced to PCE as the Figure 1 shown.  The PCE can
   calculate the SR paths and a SR path can be initiated by PCE or PCC.






























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                                       |
                                       |
                                       V
                                   +---+--+
                    +--------------+ PCE  +---------------+
                    |              +---+--+               |
            +-------|-------------------------------------|--------+
            |       |             SR network              |        |
            |       |                                     |        |
            |   +---+--+           +---+--+           +---+--+     |
            |   |  A   +-----------+   B  +-----------+   C  +     |
            |   +------+           +------+           +------+     |
            |                                                      |
            +------------------------------------------------------+

           Ingress Node:                         Egress Node:

           Reverse Path Label                    Forward Path Label
              (Incoming Label)                       (Outgoing Label)

   SR Label Stacks:

           +--------------------+                +--------------------+
           |       Label A      |                |      Label C       |
           +--------------------+                +--------------------+
           |        ...         |                |        ...         |
           +--------------------+                +--------------------+
           |       Label C      |                |      Label A       |
           +--------------------+                +--------------------+
           | Forward Path Label |                | Reverse Path Label |
           +--------------------+                +--------------------+

                Figure 1 The SR-MPLS-TP Architecture with PCE

   It is required to support bidirectional SR tunnel to meet the
   requirement of SR-MPLS-TP networks.  A label named path segment at
   both ends of the paths was defined to identify the direction of the
   SR paths as defined in [I-D.ietf-spring-mpls-path-segment].  It
   mainly aims to bind two unidirectional SR paths to a single
   bidirectional tunnel.

   As the Figure 1 shown, the forward and reverse directions of the
   bidirectional SR tunnel are identified by the forward and reverse
   path label respectively.  For the ingress node, the forward path
   label shall be added to the bottom of the label stack and the reverse
   path label shall be configured to the data plane as incoming label
   for the SR LSP.  And for the egress node, the reverse path label need




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   to be the last one label of the label stack and the forward path
   label shall be used as outgoing label.

2.1.  SR Path SID Allocation

   [RFC8402] defined the IGP, BGP, and Binding segments for the SR-MPLS
   and SRv6 data planes which can be referred as to Segment Identifier
   (SID).  And [I-D.ietf-spring-mpls-path-segment] defined a new type of
   segment named path segment.  So the path segment can also be
   identified by SID called SR path SID.  The path segment may be
   associated with a unidirectional path.

   The path SID allocation includes ingress PCC allocated, egress PCC
   allocated and PCE allocated in the domain.  In case of egress PCC
   allocated, the ingress PCC needs to comunicate with PCE to send path
   segment request to egress PCC as the Figure 2 shown.  When the
   ingress PCC requests PCE to compute the SR path with PCReq message,
   the PCE needs to request egress PCC to allocate the path SID with the
   PCUpd or PCInit message carrying the Tunnel 1 and LSP 1.  The egress
   PCC needs to identify the allocation function from the initiation
   message and should not return back PCErr message when checking the
   local address is not equal with the source address of Tunnel 1.  This
   document defines E bit in section 3.2 carried in LSP object to
   indicate the egress PCC operation which may not trigger the LSP
   initiation.

   When the path SID is allocated by ingress PCC, it need to inform PCE
   with the PCRpt message and the latter one sends the notification to
   egress PCC with PCUpd or PCInit message carried LSP object which set
   the E bit to 1.

   When the path SID is allocated by PCE, it need to inform ingress and
   egress PCC with PCUpd or PCInit message carrying the Tunnel 1 and LSP
   1.  But the message sent to egress PCC MUST set the E bit to 1 to
   avoid triggering the LSP initiation.
















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                                 +------+
                                 |  PCE |
                                 +------+
                    PCReq        ^      \   PCUpd/PCInit
                    Tunnel 1    /        \  Tunnel 1
                    LSP1       /          \ LSP1, E=1
                              /            v
                     +--------+    LSP1    +-------+
                     |Ingress |----------->|Egress |
                     |PCC     |<-----------|PCC    |
                     +--------+    LSP2    +-------+

                 Figure 2 The path SID allocation with PCE


2.2.  Associated Bi-directional SR tunnel

   As [RFC5654] defined, MPLS-TP MUST support unidirectional, co-routed
   bidirectional, and associated bidirectional point-to-point transport
   paths.  As [RFC8402] defined, segment routing leverages the source
   routing paradigm and the sourse node steers a packet through an
   ordered segment list along a unidirectional path.  So for
   bidirectional SR tunnel, the forward and backward directional paths
   may be setup by the source node and destination node seperately.

   As described in [I-D.ietf-pce-association-bidir], two reverse
   unidirectional LSPs can be associated as an associated bidirectional
   tunnel which can be initialed by single-sided and double-sided
   methods.  Based on the discussion above, the associated bidirectional
   SR tunnel can only be provisioned on both ingress and egress node
   (PCCs).

   The Single-sided initiation can be initiated by ingress SR node and
   initiate two unidirectional LSPs to headend SR nodes as shown in
   Figure 3.  The Double-sided initiation can be initiated by PCCs or
   PCE as shown in Figure 4 and 5 respectively.  The forward and reverse
   directional paths can be co-routed or non-corouted.  The SR
   bidirectional tunnel may follow the same path in the forward and
   reverse directions and initiated as a co-routed associated
   bidirectional LSP.  When the PCE initiated the LSP, the B flag need
   to be set to indicate a bi-directional LSP as defined in
   [I-D.ietf-pce-pcep-stateful-pce-gmpls].









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                         +---------+
                         |   PCE   |
                         +---------+
              1,PCReq    ^ /2,PCInit\   2,PCInit
              Tunnel 1  / / Tunnel 1 \  Tunnel 1
                       / / LSP1       \ LSP2
                      / v              v
                +--------+    LSP1    +-------+
                |Ingress |----------->|Egress |
                |PCC     |<-----------|PCC    |
                +--------+    LSP2    +-------+

    Figure 3 PCC-initiated Single-sided Associated Bi-directional LSPs

                              +---------+
                              |   PCE   |
                              +---------+
                  1,PCReq    ^ /2,PCInit \ ^   1,PCReq
                 Tunnel 1   / /  Tunnel 1 \ \   Tunnel 1
                     LSP1  / /  LSP1/LSP2  \ \  LSP2
                          / v               v \
                     +--------+    LSP1    +-------+
                     |Ingress |----------->|Egress |
                     |PCC     |<-----------|PCC    |
                     +--------+    LSP2    +-------+

    Figure 4 PCC-initiated Double-sided Associated Bi-directional LSPs

                              +---------+
                              |   PCE   |
                              +---------+
                     PCInit   /         \   PCInit
                    Tunnel 1 /           \   Tunnel 1
                      LSP1  /             \  LSP2
                           v               v
                    +--------+    LSP1    +-------+
                    |Ingress |----------->|Egress |
                    |PCC     |<-----------|PCC    |
                    +--------+    LSP2    +-------+

    Figure 5  PCE-initiated Double-sided Associated Bi-directional LSPs

3.  PCEP extensions for SR-MPLS-TP








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3.1.  ERO extension

   As described in [I-D.ietf-spring-mpls-path-segment], it is required
   to support bi-directional tunnel to meet the requirement of SR
   networks.  But it is the uni-directional tunnel for SR and
   engineering traffic network as discussed in
   [I-D.ietf-pce-segment-routing].  The SR path is carried in the
   Segment Routing Explicit Route Object (SR-ERO), which consists of a
   sequence of SR subobjects.  This document proposes the extension of
   the SR-ERO Subobject to carry the bi-directional tunnel information
   as the Figure 6 shown.  The subobjects with path SIDs need to be
   added to the list of the SR-ERO subobjects.


        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |L|    Type     |     Length    |  NT   |     Flags   |R|F|S|C|M|
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                              SID                              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       //                  NAI(variable,optional)                     //
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 6 Extension of SR-ERO Subobject format

   NAI Type (NT) : A new type of NT = 6 is added in this document and it
   indicates the type and format of the NAI associated with the path SID
   contained in the object body.  When NT is set to 6, the format of NAI
   field is shown as Figure 7.

   R (Reverse Flag -- 1 bit): indicates the SR path direction, when it
   is clear, it indicates the forward direction and when it is set, it
   indicates the reverse direction.

   The definition of other fields is the same with
   [I-D.ietf-pce-segment-routing].

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              Path Label               | TC  |S|       TTL     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                   Figure 7  NAI for Path Label information


   The format of Path Label information is specified as
   [I-D.ietf-spring-mpls-path-segment].



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3.2.  E bit in LSP object

   The LSP object is defined in [RFC8231].  This document proposes the E
   bit in flag field of the LSP object as shown in Figure 8:

   E (Egress PCC Operation bit): If the bit is set to 1, it indicates
   that the egress PCC operation with PCUpd or PCInit message and no
   need to trigger the LSP initiation.  A PCE would set the bit to 1 in
   SR network to request or inform the path SID information.

                  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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                PLSP-ID                |         Flag        |E|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     //                        TLVs                                 //
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                 Figure 8 The extension of LSP object


3.3.  Processing Rules

   As discussed in [I-D.ietf-spring-mpls-path-segment], the bi-
   directional SR tunnel is created from two binding unidirectional SR
   paths.  As defined in [RFC8281], the stateful PCE calculates the SR
   paths and initiates the bi-directional LSP with PCUpd or PCInit
   message.

   The B bit in SRP Object MUST be set and the two unidirectional SR
   paths may be computed from the forward and reverse direction and sent
   to the source and destination PCC respectively in SR-ERO object.  The
   path labels which binding the paths may be generated in PCE and sent
   to the related PCC carried in the bottom of the SR-ERO.  When the
   PCCs at both ends receiving the PCInit message with the labels in SR-
   ERO subobjects, they may forward the packets from bi-directional
   tunnel in MPLS-TP networks.

4.  Security Considerations

   TBD.

5.  IANA Considerations

   TBD.






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6.  Acknowledgements

   TBD.

7.  Normative References

   [I-D.ietf-pce-association-bidir]
              Barth, C., Gandhi, R., and B. Wen, "PCEP Extensions for
              Associated Bidirectional Label Switched Paths (LSPs)",
              draft-ietf-pce-association-bidir-02 (work in progress),
              November 2018.

   [I-D.ietf-pce-pcep-stateful-pce-gmpls]
              Lee, Y., Zhang, F., Casellas, R., Dios, O., and Z. Ali,
              "Path Computation Element (PCE) Protocol Extensions for
              Stateful PCE Usage in GMPLS-controlled Networks", draft-
              ietf-pce-pcep-stateful-pce-gmpls-10 (work in progress),
              March 2019.

   [I-D.ietf-pce-segment-routing]
              Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
              and J. Hardwick, "PCEP Extensions for Segment Routing",
              draft-ietf-pce-segment-routing-16 (work in progress),
              March 2019.

   [I-D.ietf-spring-mpls-path-segment]
              Cheng, W., Li, H., Chen, M., Gandhi, R., and R. Zigler,
              "Path Segment in MPLS Based Segment Routing Network",
              draft-ietf-spring-mpls-path-segment-00 (work in progress),
              March 2019.

   [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>.

   [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>.

   [RFC5654]  Niven-Jenkins, B., Ed., Brungard, D., Ed., Betts, M., Ed.,
              Sprecher, N., and S. Ueno, "Requirements of an MPLS
              Transport Profile", RFC 5654, DOI 10.17487/RFC5654,
              September 2009, <https://www.rfc-editor.org/info/rfc5654>.






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   [RFC8231]  Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path
              Computation Element Communication Protocol (PCEP)
              Extensions for Stateful PCE", RFC 8231,
              DOI 10.17487/RFC8231, September 2017,
              <https://www.rfc-editor.org/info/rfc8231>.

   [RFC8281]  Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "Path
              Computation Element Communication Protocol (PCEP)
              Extensions for PCE-Initiated LSP Setup in a Stateful PCE
              Model", RFC 8281, DOI 10.17487/RFC8281, December 2017,
              <https://www.rfc-editor.org/info/rfc8281>.

   [RFC8402]  Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
              July 2018, <https://www.rfc-editor.org/info/rfc8402>.

Authors' Addresses

   Quan Xiong
   ZTE Corporation
   No.6 Huashi Park Rd
   Wuhan, Hubei  430223
   China

   Phone: +86 27 83531060
   Email: xiong.quan@zte.com.cn


   Shuangping Zhan
   ZTE Corporation
   Liuxian Rd
   Shenzhen  518057
   China

   Phone: +86 755 26773770
   Email: zhan.shuangping@zte.com.cn


   Fangwei Hu
   Individual

   Email: hufwei@gmail.com








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