PCE Working Group                                                  Z. Li
Internet-Draft                                                   S. Peng
Intended status: Standards Track                     Huawei Technologies
Expires: March 5, 2021                                           M. Negi
                                                           RtBrick India
                                                                 Q. Zhao
                                                        Etheric Networks
                                                                 C. Zhou
                                                                     HPE
                                                       September 1, 2020


   PCEP Procedures and Protocol Extensions for Using PCE as a Central
                       Controller (PCECC) of LSPs
          draft-ietf-pce-pcep-extension-for-pce-controller-07

Abstract

   The Path Computation Element (PCE) is a core component of Software-
   Defined Networking (SDN) systems.  It can compute optimal paths for
   traffic across a network and can also update the paths to reflect
   changes in the network or traffic demands.

   PCE was developed to derive paths for MPLS Label Switched Paths
   (LSPs), which are supplied to the head end of the LSP using the Path
   Computation Element Communication Protocol (PCEP).  But SDN has a
   broader applicability than signaled MPLS and GMPLS traffic-engineered
   (TE) networks, and the PCE may be used to determine paths in a range
   of use cases.  PCEP has been proposed as a control protocol for use
   in these environments to allow the PCE to be fully enabled as a
   central controller.

   A PCE-based central controller (PCECC) can simplify the processing of
   a distributed control plane by blending it with elements of SDN and
   without necessarily completely replacing it.  Thus, the LSP can be
   calculated/setup/initiated and the label forwarding entries can also
   be downloaded through a centralized PCE server to each network
   devices along the path while leveraging the existing PCE technologies
   as much as possible.

   This document specifies the procedures and PCEP extensions for using
   the PCE as the central controller.

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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Copyright Notice

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   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   5
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Basic PCECC Mode  . . . . . . . . . . . . . . . . . . . . . .   5
   4.  PCEP Requirements . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Procedures for Using the PCE as the Central Controller
       (PCECC) . . . . . . . . . . . . . . . . . . . . . . . . . . .   6
     5.1.  Stateful PCE Model  . . . . . . . . . . . . . . . . . . .   6
     5.2.  New LSP Functions . . . . . . . . . . . . . . . . . . . .   6
     5.3.  New PCEP Object . . . . . . . . . . . . . . . . . . . . .   7
     5.4.  PCECC Capability Advertisement  . . . . . . . . . . . . .   7
     5.5.  LSP Operations  . . . . . . . . . . . . . . . . . . . . .   8
       5.5.1.  Basic PCECC LSP set up  . . . . . . . . . . . . . . .   8
       5.5.2.  Central Controller Instructions . . . . . . . . . . .  12
         5.5.2.1.  Label Download CCI  . . . . . . . . . . . . . . .  12
         5.5.2.2.  Label Cleanup CCI . . . . . . . . . . . . . . . .  12
       5.5.3.  PCE Initiated PCECC LSP . . . . . . . . . . . . . . .  13
       5.5.4.  PCECC LSP Update  . . . . . . . . . . . . . . . . . .  15
       5.5.5.  Re-Delegation and Cleanup . . . . . . . . . . . . . .  17



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       5.5.6.  Synchronization of Central Controllers Instructions .  17
       5.5.7.  PCECC LSP State Report  . . . . . . . . . . . . . . .  17
       5.5.8.  PCC Based Allocations . . . . . . . . . . . . . . . .  18
       5.5.9.  Binding Label . . . . . . . . . . . . . . . . . . . .  18
   6.  PCEP messages . . . . . . . . . . . . . . . . . . . . . . . .  19
     6.1.  The PCInitiate message  . . . . . . . . . . . . . . . . .  19
     6.2.  The PCRpt message . . . . . . . . . . . . . . . . . . . .  21
   7.  PCEP Objects  . . . . . . . . . . . . . . . . . . . . . . . .  22
     7.1.  OPEN Object . . . . . . . . . . . . . . . . . . . . . . .  22
       7.1.1.  PCECC Capability sub-TLV  . . . . . . . . . . . . . .  22
     7.2.  PATH-SETUP-TYPE TLV . . . . . . . . . . . . . . . . . . .  23
     7.3.  CCI Object  . . . . . . . . . . . . . . . . . . . . . . .  23
       7.3.1.  Address TLVs  . . . . . . . . . . . . . . . . . . . .  24
   8.  Implementation Status . . . . . . . . . . . . . . . . . . . .  26
     8.1.  Huawei's Proof of Concept based on ONOS . . . . . . . . .  26
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  27
     9.1.  Malicious PCE . . . . . . . . . . . . . . . . . . . . . .  27
   10. Manageability Considerations  . . . . . . . . . . . . . . . .  27
     10.1.  Control of Function and Policy . . . . . . . . . . . . .  27
     10.2.  Information and Data Models  . . . . . . . . . . . . . .  27
     10.3.  Liveness Detection and Monitoring  . . . . . . . . . . .  27
     10.4.  Verify Correct Operations  . . . . . . . . . . . . . . .  27
     10.5.  Requirements On Other Protocols  . . . . . . . . . . . .  27
     10.6.  Impact On Network Operations . . . . . . . . . . . . . .  28
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  28
     11.1.  PCEP TLV Type Indicators . . . . . . . . . . . . . . . .  28
     11.2.  PATH-SETUP-TYPE-CAPABILITY Sub-TLV Type Indicators . . .  28
     11.3.  PCECC-CAPABILITY sub-TLV's Flag field  . . . . . . . . .  28
     11.4.  Path Setup Type Registry . . . . . . . . . . . . . . . .  29
     11.5.  PCEP Object  . . . . . . . . . . . . . . . . . . . . . .  29
     11.6.  CCI Object Flag Field  . . . . . . . . . . . . . . . . .  29
     11.7.  PCEP-Error Object  . . . . . . . . . . . . . . . . . . .  29
   12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  30
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  30
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  30
     13.2.  Informative References . . . . . . . . . . . . . . . . .  32
   Appendix A.  Contributor Addresses  . . . . . . . . . . . . . . .  34
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  35

1.  Introduction

   The Path Computation Element (PCE) [RFC4655] was developed to offload
   path computation function from routers in an MPLS traffic-engineered
   network.  Since then, the role and function of the PCE has grown to
   cover a number of other uses (such as GMPLS [RFC7025]) and to allow
   delegated control [RFC8231] and PCE-initiated use of network
   resources [RFC8281].




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   According to [RFC7399], Software-Defined Networking (SDN) refers to a
   separation between the control elements and the forwarding components
   so that software running in a centralized system, called a
   controller, can act to program the devices in the network to behave
   in specific ways.  A required element in an SDN architecture is a
   component that plans how the network resources will be used and how
   the devices will be programmed.  It is possible to view this
   component as performing specific computations to place traffic flows
   within the network given knowledge of the availability of network
   resources, how other forwarding devices are programmed, and the way
   that other flows are routed.  This is the function and purpose of a
   PCE, and the way that a PCE integrates into a wider network control
   system (including an SDN system) is presented in [RFC7491].

   In early PCE implementations, where the PCE was used to derive paths
   for MPLS Label Switched Paths (LSPs), paths were requested by network
   elements (known as Path Computation Clients (PCCs)), and the results
   of the path computations were supplied to network elements using the
   Path Computation Element Communication Protocol (PCEP) [RFC5440].
   This protocol was later extended to allow a PCE to send unsolicited
   requests to the network for LSP establishment [RFC8281].

   [RFC8283] introduces the architecture for PCE as a central controller
   as an extension of the architecture described in [RFC4655] and
   assumes the continued use of PCEP as the protocol used between PCE
   and PCC.  [RFC8283] further examines the motivations and
   applicability for PCEP as a Southbound Interface (SBI), and
   introduces the implications for the protocol.
   [I-D.ietf-teas-pcecc-use-cases] describes the use cases for the PCECC
   architecture.

   A PCE-based central controller (PCECC) can simplify the processing of
   a distributed control plane by blending it with elements of SDN and
   without necessarily completely replacing it.  Thus, the LSP can be
   calculated/setup/initiated and the label forwarding entries can also
   be downloaded through a centralized PCE server to each network
   devices along the path while leveraging the existing PCE technologies
   as much as possible.

   This document specifies the procedures and PCEP protocol extensions
   for using the PCE as the central controller for static LSPs, where
   LSPs can be provisioned as explicit label instructions at each hop on
   the end-to-end path.  Each router along the path must be told what
   label-forwarding instructions to program and what resources to
   reserve.  The PCE-based controller keeps a view of the network and
   determines the paths of the end-to-end LSPs, and the controller uses
   PCEP to communicate with each router along the path of the end-to-end
   LSP.



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   While this document is focused on the procedures for the static LSPs
   (referred to as basic PCECC mode in Section 3), the mechanism and
   protocol encoding are specified in such a way that, extensions for
   other use cases is easy to achieve.  For example, the extensions for
   PCECC for Segment Routing (SR) are specified in
   [I-D.zhao-pce-pcep-extension-pce-controller-sr] and
   [I-D.dhody-pce-pcep-extension-pce-controller-srv6].

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  Terminology

   The terminology used in this document is the same as that described
   in the draft [RFC8283].

3.  Basic PCECC Mode

   In this mode, LSPs are provisioned as explicit label instructions at
   each hop on the end-to-end path.  Each router along the path must be
   told what label forwarding instructions to program and what resources
   to reserve.  The controller uses PCEP to communicate with each router
   along the path of the end-to-end LSP.

   Note that the PCE-based controller will take responsibility for
   managing some part of the MPLS label space for each of the routers
   that it controls, and may take wider responsibility for partitioning
   the label space for each router and allocating different parts for
   different uses.  This is also described in section 3.1.2. of
   [RFC8283].  For the purpose of this document, it is assumed that the
   label range to be used by a PCE is known and set on both PCEP peers.
   A future extension could add the capability to advertise the range
   via possible PCEP extensions as well (see
   [I-D.li-pce-controlled-id-space]).  The rest of the processing is
   similar to the existing stateful PCE mechanism.

   This document also allows a case where the label space is maintained
   by the PCC itself, and the labels are allocated by the PCC, in this
   case, the PCE should request the allocation from PCC as described in
   Section 5.5.8.






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4.  PCEP Requirements

   The following key requirements should be considered when designing
   the PCECC based solution:

   1.  PCEP speaker supporting this draft needs to have the capability
       to advertise its PCECC capability to its peers.

   2.  PCEP speaker needs the means to identify PCECC based LSP in the
       PCEP messages.

   3.  PCEP procedures need to allow for PCC based label allocations.

   4.  PCEP procedures need to provide a means to update (or cleanup)
       the label-download entry to the PCC.

   5.  PCEP procedures need to provide a means to synchronize the labels
       between PCE and PCC via PCEP messages.

5.  Procedures for Using the PCE as the Central Controller (PCECC)

5.1.  Stateful PCE Model

   Active stateful PCE is described in [RFC8231].  PCE as a central
   controller (PCECC) reuses existing Active stateful PCE mechanism as
   much as possible to control the LSP.

5.2.  New LSP Functions

   Several new functions are required in PCEP to support PCECC.  This
   document extends the existing messages to support the new functions
   required by PCECC:

   (PCInitiate):  a PCEP message described in [RFC8281].  PCInitiate
      message is used to set up PCE-Initiated LSP based on PCECC
      mechanism.  It is also extended for Central Controller
      Instructions (CCI) (download or cleanup the Label forwarding
      instructions in the context of this document) on all nodes along
      the path.

   (PCRpt):  a PCEP message described in [RFC8231].  PCRpt message is
      used to send PCECC LSP Reports.  It is also extended to report the
      set of Central Controller Instructions (CCI) (label forwarding
      instructions in the context of this document) received from the
      PCE.  See Section 5.5.6 for more details.

   (PCUpd):  a PCEP message described in [RFC8231].  PCUpd message is
      used to send PCECC LSP Update.



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   The new functions defined in this document are mapped onto the PCEP
   messages as shown in Table 1.

        Function                                        Message
        PCECC Capability advertisement                  Open
        Label entry Add                                 PCInitiate
        Label entry Cleanup                             PCInitiate
        PCECC Initiated LSP                             PCInitiate
        PCECC LSP Update                                PCUpd
        PCECC LSP State Report                          PCRpt
        PCECC LSP Delegation                            PCRpt
        PCECC Label Report                              PCRpt

              Table 1: Functions mapped to the PCEP messages

5.3.  New PCEP Object

   This document specifies a new PCEP object called CCI (see
   Section 7.3) for the encoding of the central controller instructions.
   In the scope of this document, this is limited to Label forwarding
   instructions.  Future documents can create new CCI object-types for
   other types of central controller instructions.  The CC-ID is the
   unique identifier for the central controller instructions in PCEP.
   The PCEP messages are extended in this document to handle the PCECC
   operations.

5.4.  PCECC Capability Advertisement

   During the PCEP Initialization Phase, PCEP Speakers (PCE or PCC)
   advertise their support of PCECC extensions.

   This document defines a new Path Setup Type (PST) [RFC8408] for
   PCECC, as follows:

   o  PST = TBD1: Path is set up via PCECC mode.

   A PCEP speaker MUST indicate its support of the function described in
   this document by sending a PATH-SETUP-TYPE-CAPABILITY TLV in the OPEN
   object with this new PST included in the PST list.

   This document also defines the PCECC Capability sub-TLV
   Section 7.1.1.  PCEP speakers use this sub-TLV to exchange
   information about their PCECC capability.  If a PCEP speaker includes
   PST=TBD1 in the PST List of the PATH-SETUP-TYPE-CAPABILITY TLV then
   it MUST also include the PCECC Capability sub-TLV inside the PATH-
   SETUP-TYPE-CAPABILITY TLV.  If the sub-TLV is absent, then the PCEP
   speaker MUST send a PCErr message with Error-Type 10 (Reception of an
   invalid object) and Error-Value TBD2 (Missing PCECC Capability sub-



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   TLV) and MUST then close the PCEP session.  If a PCEP speaker
   receives a PATH-SETUP-TYPE-CAPABILITY TLV with a PCECC-CAPABILITY
   sub-TLV, but the PST list does not contain PST=TBD1, then the PCEP
   speaker MUST ignore the PCECC-CAPABILITY sub-TLV.

   The presence of the PST=TBD1 and PCECC Capability sub-TLV in a PCC's
   OPEN Object indicates that the PCC is willing to function as a PCECC
   client.  The presence of the PST=TBD1 and PCECC Capability sub-TLV in
   a PCE's OPEN message indicates that the PCE is interested in function
   as a PCECC server.

   The PCEP protocol extensions for PCECC MUST NOT be used if one or
   both PCEP Speakers have not included the PST=TBD1 or the PCECC
   Capability sub-TLV in their respective OPEN message.  If the PCEP
   Speakers support the extensions of this draft but did not advertise
   this capability attempts a PCECC operation then a PCErr message with
   Error-Type=19(Invalid Operation) and Error-Value=TBD3 (Attempted
   PCECC operations when PCECC capability was not advertised) will be
   generated and the PCEP session will be terminated.  If a PCEP speaker
   does not recognize the PCECC Capability sub-TLV, it will ignore the
   sub-TLV in accordance with [RFC8408] and [RFC5440].

   A PCC or a PCE MUST include both PCECC-CAPABILITY sub-TLV and
   STATEFUL-PCE-CAPABILITY TLV ([RFC8231]) (with I flag set [RFC8281])
   in OPEN Object to support the extensions defined in this document.
   If PCECC-CAPABILITY sub-TLV is advertised and STATEFUL-PCE-CAPABILITY
   TLV is not advertised in OPEN Object, it MUST send a PCErr message
   with Error-Type=19 (Invalid Operation) and Error-value=TBD4 (stateful
   PCE capability was not advertised) and terminate the session.  This
   error is also triggered if PCECC-CAPABILITY sub-TLV is advertised and
   I flag in the STATEFUL-PCE-CAPABILITY TLV is not set.

5.5.  LSP Operations

   The PCEP messages pertaining to PCECC MUST include PATH-SETUP-TYPE
   TLV [RFC8408] in the SRP object to clearly identify the PCECC LSP is
   intended.

5.5.1.  Basic PCECC LSP set up

   In order to set up an LSP based on the PCECC mechanism, a PCC MUST
   delegate the LSP by sending a PCRpt message with PST set for PCECC
   (see Section 7.2) and D (Delegate) flag (see [RFC8231]) set in the
   LSP object.

   An LSP-IDENTIFIER TLV MUST be included for PCECC LSP, the tuple
   uniquely identifies the LSP in the network.  The LSP object is
   included in the central controller instructions (label download) to



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   identify the PCECC LSP for this instruction.  The PLSP-ID is the
   original identifier used by the ingress PCC, so the transit LSR could
   have multiple central controller instructions that have the same
   PLSP-ID.  The PLSP-ID in combination with the source (in LSP-
   IDENTIFIER TLV) MUST be unique.  The PLSP-ID is included for
   maintainability reasons to ease debugging.  As per [RFC8281], the LSP
   object could include SPEAKER-ENTITY-ID TLV to identify the PCE that
   initiated these instructions.  Also, the CC-ID is unique in the PCEP
   session as described in Section 7.3.

   When a PCE receives a PCRpt message with D flag and PST Type set, it
   calculates the path and assigns labels along the path; and sets up
   the path by sending PCInitiate message to each node along the path of
   the LSP.  The PCC generates a Path Computation State Report (PCRpt)
   and includes the central controller instruction (CCI) and the
   identified LSP.  The CC-ID uniquely identifies the central controller
   instruction within a PCEP session.  The PCC further responds with the
   PCRpt messages including the CCI and LSP objects.

   The Ingress node would receive one CCI object with O bit (out-label)
   set.  The transit node(s) would receive two CCI objects with the in-
   label CCI without an O bit set and the out-label CCI with O bit set.
   The egress node would receive one CCI object without O bit set.  A
   node can determine its role based on the setting of the O bit in the
   CCI object(s) and the LSP-IDENTIFIER TLV in the LSP object.

   Once the central controller instructions (label operations) are
   completed, the PCE MUST send the PCUpd message to the Ingress PCC.
   Per [RFC8231], this PCUpd message should include the path information
   calculated by the PCE.

   Note that the PCECC LSPs MUST be delegated to a PCE at all times.

   LSP deletion operation for PCECC LSP is the same as defined in
   [RFC8231].  If the PCE receives a PCRpt message for LSP deletion then
   it does Label cleanup operation as described in Section 5.5.2.2 for
   the corresponding LSP.

   The Basic PCECC LSP setup sequence is as shown in Figure 1.












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                  +-------+                             +-------+
                  |PCC    |                             |  PCE  |
                  |Ingress|                             +-------+
           +------|       |                                 |
           | PCC  +-------+                                 |
           | Transit| |                                     |
    +------|        | |-- PCRpt,PLSP-ID=1, PST=TBD1, D=1--->| PCECC LSP
    |PCC   +--------+ |                                     |
    |Egress  |  |     |                                     |
    +--------+  |     |                                     |
        |       |     |                                     |
        |<------ PCInitiate,CC-ID=X,PLSP-ID=1  ------------ | Label
        |       |     |     L1,O=0                          | download
        |------- PCRpt,CC-ID=X,PLSP-ID=1  ----------------->| CCI
        |       |     |                                     |
        |       |<----- PCInitiate,PLSP-ID=1, ------------- | Labels
        |       |     |            CC-ID=Y1,O=0,L2          | download
        |       |     |            CC-ID=Y2,O=1,L1          | CCI
        |       |-----  PCRpt,CC-ID=Y1,Y2,PLSP-ID=1  ------>|
        |       |     |                                     |
        |       |     |<--- PCInitiate,CC-ID=Z,PLSP-ID=1  - | Label
        |       |     |                L2,O=1               | download
        |       |     |---- PCRpt,CC-ID=Z,PLSP-ID=1  ------>| CCI
        |       |     |                                     |
        |       |     |<-- PCUpd,PLSP-ID=1,PST=TBD1, D=1----| PCECC LSP
        |       |     |                                     | Update
        |       |     |                                     |


                      Figure 1: Basic PCECC LSP setup

   The PCECC LSPs are considered to be 'up' by default (on receipt of
   PCUpd message from PCE).  The Ingress MAY further choose to deploy a
   data plane check mechanism and report the status back to the PCE via
   a PCRpt message to make sure that the correct label instructions are
   made along the path of the PCECC LSP (and it is ready to carry
   traffic).

   In the case where the label allocations are made by the PCC itself
   (see Section 5.5.8), the PCE could request an allocation to be made
   by the PCC, and where the PCC would send a PCRpt with the allocated
   label encoded in the CC-ID object as shown in Figure 2.









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                  +-------+                             +-------+
                  |PCC    |                             |  PCE  |
                  |Ingress|                             +-------+
           +------|       |                                 |
           | PCC  +-------+                                 |
           | Transit| |                                     |
    +------|        | |-- PCRpt,PLSP-ID=1, PST=TBD1, D=1--->| PCECC LSP
    |PCC   +--------+ |                                     |
    |Egress  |  |     |                                     |
    +--------+  |     |                                     |
        |       |     |                                     |
        |<------ PCInitiate,CC-ID=X,PLSP-ID=1  ------------ | Label
        |       |     |     C=1                             | download
        |------- PCRpt,CC-ID=X,PLSP-ID=1  ----------------->| CCI
        |       |     |     Label=L1                        |
        |       |<----- PCInitiate,PLSP-ID=1, ------------- | Labels
        |       |     |            CC-ID=Y1,C=1             | download
        |       |     |            CC-ID=Y2,C=0,L1          | CCI
        |       |-----  PCRpt,PLSP-ID=1  ------------------>|
        |       |     |       CC-ID=Y1, Label=L2            |
        |       |     |       CC-ID=Y2                      |
        |       |     |<--- PCInitiate,CC-ID=Z,PLSP-ID=1  - | Label
        |       |     |                C=0,L2               | download
        |       |     |---- PCRpt,CC-ID=Z,PLSP-ID=1  ------>| CCI
        |       |     |                                     |
        |       |     |<-- PCUpd,PLSP-ID=1,PST=TBD1, D=1----| PCECC LSP
        |       |     |                                     | Update
        |       |     |                                     |

    - The O bit is set as before (and thus not included)


             Figure 2: Basic PCECC LSP setup (PCC allocation)

   It should be noted that in this example, the request is made to the
   egress node with the C bit set in the CCI object to indicate that the
   label allocation needs to be done by the egress and the egress
   responds with the allocated label to the PCE.  The PCE would further
   inform the transit PCC without setting the C bit in the CCI object
   for out-label but the C-bit is set for in-label so the transit node
   make the label allocation (for the in-label) and report to the PCE.
   Similarly, the C bit is unset towards the ingress to complete all the
   label allocation for the PCECC LSP.








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5.5.2.  Central Controller Instructions

   The new central controller instructions (CCI) for the label
   operations in PCEP is done via the PCInitiate message, by defining a
   new PCEP Object for CCI operations.  The local label range of each
   PCC is assumed to be known at both the PCC and the PCE.

5.5.2.1.  Label Download CCI

   In order to set up an LSP based on PCECC, the PCE sends a PCInitiate
   message to each node along the path to download the Label instruction
   as described in Section 5.5.1.

   The CCI object MUST be included, along with the LSP object in the
   PCInitiate message.  The LSP-IDENTIFIER TLV MUST be included in the
   LSP object.  The SPEAKER-ENTITY-ID TLV SHOULD be included in the LSP
   object.

   If a node (PCC) receives a PCInitiate message which includes a Label
   to download as part of CCI, that is out of the range set aside for
   the PCE, it MUST send a PCErr message with Error-type=TBD5 (PCECC
   failure) and Error-value=TBD6 (Label out of range) and MUST include
   the SRP object to specify the error is for the corresponding label
   update via PCInitiate message.  If a PCC receives a PCInitiate
   message but failed to download the Label entry, it MUST send a PCErr
   message with Error-type=TBD5 (PCECC failure) and Error-value=TBD7
   (instruction failed) and MUST include the SRP object to specify the
   error is for the corresponding label update via PCInitiate message.

   A new PCEP object for central controller instructions (CCI) is
   defined in Section 7.3.

5.5.2.2.  Label Cleanup CCI

   In order to delete an LSP based on PCECC, the PCE sends a central
   controller instructions via a PCInitiate message to each node along
   the path of the LSP to cleanup the Label forwarding instruction.

   If the PCC receives a PCInitiate message but does not recognize the
   label in the CCI, the PCC MUST generate a PCErr message with Error-
   Type 19(Invalid operation) and Error-Value=TBD8, "Unknown Label" and
   MUST include the SRP object to specify the error is for the
   corresponding label cleanup (via PCInitiate message).

   The R flag in the SRP object defined in [RFC8281] specifies the
   deletion of Label Entry in the PCInitiate message.





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                  +-------+                              +-------+
                  |PCC    |                              |  PCE  |
                  |Ingress|                              +-------+
           +------|       |                                  |
           | PCC  +-------+                                  |
           | Transit| |                                      |
    +------|        | |-- PCRpt,PLSP-ID=1,PST=TBD1,D=1,R=1-->| PCECC LSP
    |PCC   +--------+ |                                      | remove
    |Egress  |  |     |                                      |
    +--------+  |     |                                      |
        |       |     |                                      |
        |<------ PCInitiate,CC-ID=X,PLSP-ID=1  ------------  | Label
        |       |     |                   R=1                | cleanup
        |------- PCRpt,CC-ID=X,PLSP-ID=1  ------------------>| CCI
        |       |     |                                      |
        |       |<----- PCInitiate,CC-ID=Y1,Y2,PLSP-ID=1  -- | Label
        |       |     |                          R=1         | cleanup
        |       |-----  PCRpt,CC-ID=Y1,Y2,PLSP-ID=1  ------->| CCI
        |       |     |                                      |
        |       |     |<--- PCInitiate,CC-ID=Z,PLSP-ID=1  -- | Label
        |       |     |                              R=1     | cleanup
        |       |     |---- PCRpt,CC-ID=Z,PLSP-ID=1  ------->| CCI
        |       |     |                                      |


                          Figure 3: Label Cleanup

   As per [RFC8281], following the removal of the Label forwarding
   instruction, the PCC MUST send a PCRpt message.  The SRP object in
   the PCRpt MUST include the SRP-ID-number from the PCInitiate message
   that triggered the removal.  The R flag in the SRP object MUST be
   set.

   In the case where the label allocation is made by the PCC itself (see
   Section 5.5.8), the removal procedure remains the same.

5.5.3.  PCE Initiated PCECC LSP

   The LSP Instantiation operation is the same as defined in [RFC8281].

   In order to set up a PCE Initiated LSP based on the PCECC mechanism,
   a PCE sends PCInitiate message with Path Setup Type set for PCECC
   (see Section 7.2) to the Ingress PCC.

   The Ingress PCC MUST also set D (Delegate) flag (see [RFC8231]) and C
   (Create) flag (see [RFC8281]) in the LSP object of PCRpt message.
   The PCC responds with a PCRpt message with the status set to "GOING-
   UP" and carrying the assigned PLSP-ID.



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   Note that the label forwarding instructions from PCECC are sent after
   the initial PCInitiate and PCRpt exchange.  This is done so that the
   PLSP-ID and other LSP identifiers can be obtained from the ingress
   and can be included in the label forwarding instruction in the next
   PCInitiate message.  The rest of the PCECC LSP setup operations are
   the same as those described in Section 5.5.1.

   The LSP deletion operation for PCE Initiated PCECC LSP is the same as
   defined in [RFC8281].  The PCE should further perform Label entry
   cleanup operation as described in Section 5.5.2.2 for the
   corresponding LSP.

   The PCE Initiated PCECC LSP setup sequence is shown in Figure 4.


                 +-------+                              +-------+
                 |PCC    |                              |  PCE  |
                 |Ingress|                              +-------+
          +------|       |                                  |
          | PCC  +-------+                                  |
          | Transit| |                                      |
   +------|        | |<--PCInitiate,PLSP-ID=0,PST=TBD1,D=1--| PCECC LSP
   |PCC   +--------+ |                                      | Initiate
   |Egress  |  |     |--- PCRpt,PLSP-ID=2,P=1,D=1,C=1--->   | PCECC LSP
   +--------+  |     |       (GOING-UP)                     |
       |       |     |                                      |
       |<------ PCInitiate,CC-ID=X,PLSP-ID=2 -------------- | Label
       |       |     |                                      | download
       |------- PCRpt,CC-ID=X,PLSP-ID=2  ------------------>| CCI
       |       |     |                                      |
       |       |<----- PCInitiate,CC-ID=Y1,Y2,PLSP-ID=2 --- | Label
       |       |     |                                      | download
       |       |-----  PCRpt,CC-ID=Y1,Y2,PLSP-ID=2  ------->| CCI
       |       |     |                                      |
       |       |     |<--- PCInitiate,CC-ID=Z,PLSP-ID=2 --- | Label
       |       |     |                                      | download
       |       |     |---- PCRpt,CC-ID=Z,PLSP-ID=2  ------->| CCI
       |       |     |                                      |
       |       |     |<-- PCUpd, PLSP-ID=2, PST=TBD1, D=1-- | PCECC LSP
       |       |     |      (UP)                            | Update
       |       |     |--- PCRpt,PLSP-ID=2,P=1,D=1,C=1--->   |
       |       |     |      (UP)                            |


                     Figure 4: PCE Initiated PCECC LSP

   Once the label operations are completed, the PCE SHOULD send a PCUpd
   message to the Ingress PCC.  The PCUpd message is as per [RFC8231].



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   In the case where the label allocations are made by the PCC itself
   (see Section 5.5.8), the procedure remains the same.

5.5.4.  PCECC LSP Update

   In case of a modification of a PCECC LSP with a new path, a PCE sends
   a PCUpd message to the Ingress PCC.  But to follow the make-before-
   break procedures, the PCECC first update new instructions based on
   the updated LSP and then update to ingress to switch traffic, before
   cleaning up the old instructions.  A new CC-ID is used to identify
   the updated instruction, the existing identifiers in the LSP object
   identify the existing LSP.  Once new instructions are downloaded, the
   PCE further updates the new path at the ingress which triggers the
   traffic switch on the updated path.  The Ingress PCC acknowledges
   with a PCRpt message, on receipt of the PCRpt message, the PCE does
   cleanup operation for the old LSP as described in Section 5.5.2.2.

   The PCECC LSP Update sequence is shown in Figure 5.

































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                 +-------+                             +-------+
                 |PCC    |                             |  PCE  |
                 |Ingress|                             +-------+
          +------|       |                                 |
          | PCC  +-------+                                 |
          | Transit| |                                     |
   +------|        | |                                     |
   |PCC   +--------+ |                                     |
   |Egress  |  |     |                                     |
   +--------+  |     |                                     |
       |       |     |                                     | New Path
       |<------ PCInitiate,CC-ID=XX,PLSP-ID=1 -----------  | for LSP
       |       |     |                                     | trigger
       |------- PCRpt,CC-ID=XX,PLSP-ID=1  ---------------->| new CCI
       |       |     |                                     |
       |       |<----- PCInitiate,CC-ID=YY1,YY2,PLSP-ID=1--| Label
       |       |     |                                     | download
       |       |-----  PCRpt,CC-ID=YY1,YY2,PLSP-ID=1  ---->| CCI
       |       |     |                                     |
       |       |     |<--- PCInitiate,CC-ID=ZZ,PLSP-ID=1 - | Label
       |       |     |                                     | download
       |       |     |---- PCRpt,CC-ID=ZZ,PLSP-ID=1  ----->| CCI
       |       |     |                                     |
       |       |     |<-- PCUpd, PLSP-ID=1, PST=TBD1, D=1- | PCECC
       |       |     |    SRP=S                            | LSP Update
       |       |     |                                     |
       |       |     |-- PCRpt,PLSP-ID=1,PST=TBD1,D=1   -->| Trigger
       |       |     |       (SRP=S)                       | Delete old
       |       |     |                                     | CCI
       |       |     |                                     |
       |<------ PCInitiate,CC-ID=X, PLSP-ID=1 -----------  | Label
       |       |     |                    R=1              | cleanup
       |------- PCRpt,CC-ID=X, PLSP-ID=1  ---------------->| CCI
       |       |     |                                     |
       |       |<----- PCInitiate,CC-ID=Y1,Y2, PLSP-ID=1 - | Label
       |       |     |                           R=1       | cleanup
       |       |-----  PCRpt,CC-ID=Y1,Y2, PLSP-ID=1  ----->| CCI
       |       |     |                                     |
       |       |     |<--- PCInitiate,CC-ID=Z, PLSP-ID=1 - | Label
       |       |     |                               R=1   | cleanup
       |       |     |---- PCRpt,CC-ID=Z, PLSP-ID=1  ----->| CCI
       |       |     |                                     |


                        Figure 5: PCECC LSP Update






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   The modified PCECC LSPs are considered to be 'up' by default.  The
   Ingress MAY further choose to deploy a data plane check mechanism and
   report the status back to the PCE via a PCRpt message.

   In the case where the label allocations are made by the PCC itself
   (see Section 5.5.8), the procedure remains the same.

5.5.5.  Re-Delegation and Cleanup

   As described in [RFC8281], a new PCE can gain control over an
   orphaned LSP.  In the case of a PCECC LSP, the new PCE MUST also gain
   control over the central controller instructions in the same way by
   sending a PCInitiate message that includes the SRP, LSP, and CCI
   objects and carries the CC-ID and PLSP-ID identifying the
   instruction, it wants to take control of.

   Further, as described in [RFC8281], the State Timeout Interval timer
   ensures that a PCE crash does not result in automatic and immediate
   disruption for the services using PCE-initiated LSPs.  Similarly the
   central controller instructions are not removed immediately upon PCE
   failure.  Instead, they are cleaned up on the expiration of this
   timer.  This allows for network cleanup without manual intervention.
   The PCC MUST support the removal of CCI as one of the behaviors
   applied on expiration of the State Timeout Interval timer.

5.5.6.  Synchronization of Central Controllers Instructions

   The purpose of Central Controllers Instructions synchronization
   (labels in the context of this document) is to make sure that the
   PCE's view of CCI (Labels) matches with the PCC's Label allocation.
   This synchronization is performed as part of the LSP state
   synchronization as described in [RFC8231] and [RFC8233].

   As per LSP State Synchronization [RFC8231], a PCC reports the state
   of its LSPs to the PCE using PCRpt messages and as per [RFC8281], PCE
   would initiate any missing LSPs and/or remove any LSPs that are not
   wanted.  The same PCEP messages and procedures are also used for the
   Central Controllers Instructions synchronization.  The PCRpt message
   includes the CCI and the LSP object to report the label forwarding
   instructions.  The PCE would further remove any unwanted instructions
   or initiate any missing instructions.

5.5.7.  PCECC LSP State Report

   As mentioned before, an Ingress PCC MAY choose to apply any OAM
   mechanism to check the status of LSP in the Data plane and MAY
   further send its status in a PCRpt message to the PCE.




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5.5.8.  PCC Based Allocations

   The PCE can request the PCC to allocate the label using the
   PCInitiate message.  The C flag in the CCI object is set to 1 to
   indicate that the allocation needs to be done by the PCC.  The PCC
   would allocate the Label and would report to the PCE using the PCRpt
   message.

   If the value of the Label is 0 and the C flag is set, it indicates
   that the PCE is requesting the allocation to be done by the PCC.  If
   the Label is 'n' and the C flag is set in the CCI object, it
   indicates that the PCE requests a specific value 'n' for the Label.
   If the allocation is successful, the PCC should report via the PCRpt
   message with the CCI object.  Else, it MUST send a PCErr message with
   Error-Type = TBD5 ("PCECC failure") and Error Value = TBD9 ("Invalid
   CCI").  If the value of the Label in the CCI object is valid, but the
   PCC is unable to allocate it, it MUST send a PCErr message with
   Error-Type = TBD5 ("PCECC failure") and Error Value = TBD10 ("Unable
   to allocate the specified CCI").

   If the PCC wishes to withdraw or modify the previously assigned
   label, it MUST send a PCRpt message without any Label or with the
   Label containing the new value respectively in the CCI object.  The
   PCE would further trigger the removal of the central controller
   instruction as per this document.

5.5.9.  Binding Label

   As per [I-D.ietf-pce-binding-label-sid], when a stateful PCE is
   deployed for setting up TE paths, it may be desirable to report the
   binding label to the stateful PCE for the purpose of enforcing end-
   to-end TE.  In the case of the PCECC, the binding label may be
   allocated by the PCE itself as described in this section.  This
   procedure is thus applicable for all path setup types including
   PCECC.

   A P flag in the LSP object is introduced in
   [I-D.ietf-pce-sr-path-segment] to indicate the allocation needs to be
   made by the PCE.  This flag is used to indicate that the allocation
   needs to be made by the PCE.  A PCC would set this bit to 1 (and
   carry the TE-PATH-BINDING TLV [I-D.ietf-pce-binding-label-sid] in the
   LSP object) to request for allocation of the binding label by the PCE
   in the PCReq or PCRpt message.  A PCE would also set this bit to 1 to
   indicate that the binding label is allocated by PCE and encoded in
   the PCRep, PCUpd, or PCInitiate message (the TE-PATH-BINDING TLV is
   present in LSP object).  Further, a PCE would set this bit to 0 to
   indicate that the allocation is done by the PCC instead.




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   The ingress PCC could request the binding label to be allocated by
   the PCE via a PCRpt message as per [RFC8231].  The delegate flag
   (D-flag) MUST also be set for this LSP.  The TE-PATH-BINDING TLV MUST
   be included with no Binding Value.  The PCECC would allocate the
   binding label and further respond to Ingress PCC with PCUpd message
   as per [RFC8231] and MUST include the TE-PATH-BINDING TLV in an LSP
   object.  The P flag in the LSP object would be set to 1 to indicate
   that the allocation is made by the PCE.

   The PCE could allocate the binding label on its own accord for a PCE-
   Initiated (or delegated LSP).  The allocated binding label needs to
   be informed to the PCC.  The PCE would use the PCInitiate message
   [RFC8281] or PCUpd message [RFC8231] towards the PCC and MUST include
   the TE-PATH-BINDING TLV in the LSP object.  The P flag in the LSP
   object would be set to 1 to indicate that the allocation is made by
   the PCE.

   Before a PCE can allocate a binding label the PCECC capability MUST
   be exchanged on the PCEP session.  Note that the CCI object is not
   used for binding allocation; this is done to maintain consistency
   with the rest of the binding label/SID procedures as per
   [I-D.ietf-pce-binding-label-sid].

6.  PCEP messages

   As defined in [RFC5440], a PCEP message consists of a common header
   followed by a variable-length body made of a set of objects that can
   be either mandatory or optional.  An object is said to be mandatory
   in a PCEP message when the object must be included for the message to
   be considered valid.  For each PCEP message type, a set of rules is
   defined that specify the set of objects that the message can carry.
   An implementation MUST form the PCEP messages using the object
   ordering specified in this document.

   LSP-IDENTIFIERS TLV MUST be included in the LSP object for PCECC LSP.

   The message formats in this document are specified using Routing
   Backus-Naur Form (RBNF) encoding as specified in [RFC5511].

6.1.  The PCInitiate message

   The PCInitiate message [RFC8281] can be used to download or remove
   the labels, this document extends the message as shown below -








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        <PCInitiate Message> ::= <Common Header>
                                 <PCE-initiated-lsp-list>
     Where:
        <Common Header> is defined in [RFC5440]

        <PCE-initiated-lsp-list> ::= <PCE-initiated-lsp-request>
                                     [<PCE-initiated-lsp-list>]

        <PCE-initiated-lsp-request> ::=
                               (<PCE-initiated-lsp-instantiation>|
                                <PCE-initiated-lsp-deletion>|
                                <PCE-initiated-lsp-central-control>)

        <PCE-initiated-lsp-central-control> ::= <SRP>
                                                <LSP>
                                                <cci-list>

        <cci-list> ::=  <CCI>
                        [<cci-list>]

     Where:
        <PCE-initiated-lsp-instantiation> and
        <PCE-initiated-lsp-deletion> are as per
         [RFC8281].

        The LSP and SRP object is defined in [RFC8231].


   When PCInitiate message is used for the central controller
   instructions (labels), the SRP, LSP, and CCI objects MUST be present.
   The SRP object is defined in [RFC8231] and if the SRP object is
   missing, the receiving PCC MUST send a PCErr message with Error-
   type=6 (Mandatory Object missing) and Error-value=10 (SRP object
   missing).  The LSP object is defined in [RFC8231] and if the LSP
   object is missing, the receiving PCC MUST send a PCErr message with
   Error-type=6 (Mandatory Object missing) and Error-value=8 (LSP object
   missing).  The CCI object is defined in Section 7.3 and if the CCI
   object is missing, the receiving PCC MUST send a PCErr message with
   Error-type=6 (Mandatory Object missing) and Error-value=TBD11 (CCI
   object missing).  More than one CCI object MAY be included in the
   PCInitiate message for the transit LSR.

   To cleanup, the SRP object must set the R (remove) bit and include
   the LSP and the CCI object.

   The CCI object received at the Ingress node MUST have the O bit (out-
   label) set.  The CCI Object received at the egress MUST have the O
   bit unset.  If this is not the case, PCC MUST send a PCErr message



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   with Error-Type = TBD5 ("PCECC failure") and Error Value = TBD9
   ("Invalid CCI").  Other instances of the CCI object if present, MUST
   be ignored.

   At most two instances of CCI object would be included in the case of
   transit LSR to encode both in-coming and out-going label forwarding
   instructions.  Other instances MUST be ignored.  If the transit LSR
   did not receive two CCI object with one of them having the O bit set
   and another with O bit unset, it MUST send a PCErr message with
   Error-Type = TBD5 ("PCECC failure") and Error Value = TBD9 ("Invalid
   CCI").

6.2.  The PCRpt message

   The PCRpt message can be used to report the labels that were
   allocated by the PCE, to be used during the state synchronization
   phase.


         <PCRpt Message> ::= <Common Header>
                             <state-report-list>
      Where:

         <state-report-list> ::= <state-report>[<state-report-list>]

         <state-report> ::= (<lsp-state-report>|
                             <central-control-report>)

         <lsp-state-report> ::= [<SRP>]
                                <LSP>
                                <path>

         <central-control-report> ::= [<SRP>]
                                      <LSP>
                                      <cci-list>

         <cci-list> ::=  <CCI>
                         [<cci-list>]

       Where:
         <path> is as per [RFC8231] and the LSP and SRP object are
         also defined in [RFC8231].

   When PCRpt message is used to report the central controller
   instructions (labels), the LSP and CCI objects MUST be present.  The
   LSP object is defined in [RFC8231] and if the LSP object is missing,
   the receiving PCE MUST send a PCErr message with Error-type=6
   (Mandatory Object missing) and Error-value=8 (LSP object missing).



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   The CCI object is defined in Section 7.3 and if the CCI object is
   missing, the receiving PCC MUST send a PCErr message with Error-
   type=6 (Mandatory Object missing) and Error-value=TBD11 (CCI object
   missing).  Two CCI objects can be included in the PCRpt message for
   the transit LSR.

7.  PCEP Objects

   The PCEP object defined in this document are compliant with the PCEP
   object format defined in [RFC5440].

7.1.  OPEN Object

   This document defines new optional TLVs for use in the OPEN Object.

7.1.1.  PCECC Capability sub-TLV

   The PCECC-CAPABILITY sub-TLV is an optional TLV for use in the OPEN
   Object for PCECC capability advertisement in PATH-SETUP-TYPE-
   CAPABILITY TLV.  Advertisement of the PCECC capability implies
   support of LSPs that are set up through PCECC as per PCEP extensions
   defined in this document.

   Its format is shown in Figure 6.


       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=TBD12      |          Length=4             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             Flags                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                    Figure 6: PCECC Capability sub-TLV

   The type of the TLV is TBD12 and it has a fixed length of 4 octets.

   The value comprises a single field - Flags (32 bits).

   No flags are defined in this document.

   Unassigned bits MUST be set to 0 on transmission and MUST be ignored
   on receipt.






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7.2.  PATH-SETUP-TYPE TLV

   The PATH-SETUP-TYPE TLV is defined in [RFC8408]; this document
   defines a new PST value:

   o  PST = TBD1: Path is set up via PCECC mode.

   On a PCRpt/PCUpd/PCInitiate message, the PST=TBD1 in PATH-SETUP-TYPE
   TLV in SRP object indicates that this LSP was set up via a PCECC
   based mechanism.

7.3.  CCI Object

   The Central Controller Instructions (CCI) Object is used by the PCE
   to specify the forwarding instructions (Label information in the
   context of this document) to the PCC, and MAY be carried within
   PCInitiate or PCRpt message for label download.

   CCI Object-Class is TBD13.

   CCI Object-Type is 1 for the MPLS Label.


    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            CC-ID                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Reserved             |             Flags         |C|O|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Label                 |     Reserved          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                        Optional TLV                         //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                           Figure 7: CCI Object

   The fields in the CCI object are as follows:

   CC-ID:  A PCEP-specific identifier for the CCI information.  A PCE
      creates a CC-ID for each instruction, the value is unique within
      the scope of the PCE and is constant for the lifetime of a PCEP
      session.  The values 0 and 0xFFFFFFFF are reserved and MUST NOT be
      used.




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   Flags:  is used to carry any additional information pertaining to the
      CCI.  Currently, the following flag bits are defined:

      *  O bit(Out-label) : If the bit is set, it specifies the label is
         the OUT label and it is mandatory to encode the next-hop
         information (via IPV4-ADDRESS TLV or IPV6-ADDRESS TLV or
         UNNUMBERED-IPV4-ID-ADDRESS TLV in the CCI object).  If the bit
         is not set, it specifies the label is the IN label and it is
         optional to encode the local interface information (via
         IPV4-ADDRESS TLV or IPV6-ADDRESS TLV or UNNUMBERED-IPV4-ID-
         ADDRESS TLV in the CCI object).

      *  C-Bit (PCC Allocation): If the bit is set to 1, it indicates
         that the allocation needs to be done by the PCC for this
         central controller instruction.  A PCE sets this bit to request
         the PCC to make an allocation from its label space.  A PCC
         would set this bit to indicate that it has allocated the CC-ID
         and report it to the PCE.

      *  All unassigned bits MUST be set to zero at transmission and
         ignored at receipt.

   Label (20-bit):  The Label information.

   Reserved (12 bit):  Set to zero while sending, ignored on receive.

7.3.1.  Address TLVs

   This document defines the following TLVs for the CCI object to
   associate the next-hop information in the case of an outgoing label
   and local interface information in the case of an incoming label.


   IPV4-ADDRESS TLV:

    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=TBD14        |  Length = 4                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        IPv4 address                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   IPV6-ADDRESS TLV:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



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   |             Type=TBD15        |   Length = 16                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                IPv6 address (16 bytes)                      //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   UNNUMBERED-IPV4-ID-ADDRESS TLV:

    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=TBD16        |   Length = 8                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Node-ID                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Interface ID                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   LINKLOCAL-IPV6-ID-ADDRESS TLV:

    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=TBD17        |   Length = 40                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   //               Local IPv6 address (16 octets)                //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Local Interface ID                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   //               Remote IPv6 address (16 octets)               //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Remote Interface ID                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                          Figure 8: Address TLVs

   The address TLVs are as follows:

   IPV4-ADDRESS TLV:  an IPv4 address.

   IPV6-ADDRESS TLV:  an IPv6 address.

   UNNUMBERED-IPV4-ID-ADDRESS TLV:  a Node ID / Interface ID tuple.

   LINKLOCAL-IPV6-ID-ADDRESS TLV:  a pair of (global IPv6 address,
      interface ID) tuples.



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8.  Implementation Status

   [Note to the RFC Editor - remove this section before publication, as
   well as remove the reference to RFC 7942.]

   This section records the status of known implementations of the
   protocol defined by this specification at the time of posting of this
   Internet-Draft, and is based on a proposal described in [RFC7942].
   The description of implementations in this section is intended to
   assist the IETF in its decision processes in progressing drafts to
   RFCs.  Please note that the listing of any individual implementation
   here does not imply endorsement by the IETF.  Furthermore, no effort
   has been spent to verify the information presented here that was
   supplied by IETF contributors.  This is not intended as, and must not
   be construed to be, a catalog of available implementations or their
   features.  Readers are advised to note that other implementations may
   exist.

   According to [RFC7942], "this will allow reviewers and working groups
   to assign due consideration to documents that have the benefit of
   running code, which may serve as evidence of valuable experimentation
   and feedback that have made the implemented protocols more mature.
   It is up to the individual working groups to use this information as
   they see fit".

8.1.  Huawei's Proof of Concept based on ONOS

   The PCE function was developed in the ONOS open source platform.
   This extension was implemented on a private version as a proof of
   concept for PCECC.

   o  Organization: Huawei

   o  Implementation: Huawei's PoC based on ONOS

   o  Description: PCEP as a southbound plugin was added to ONOS.  To
      support PCECC, an earlier version of this I-D was implemented.
      Refer https://wiki.onosproject.org/display/ONOS/PCEP+Protocol

   o  Maturity Level: Prototype

   o  Coverage: Partial

   o  Contact: satishk@huawei.com







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9.  Security Considerations

   The security considerations described in [RFC8231] and [RFC8281]
   apply to the extensions described in this document.  Additional
   considerations related to a malicious PCE are introduced.

9.1.  Malicious PCE

   PCE has complete control over PCC to update the labels and can cause
   the LSP's to behave inappropriately and cause major impact to the
   network.  As a general precaution, it is RECOMMENDED that this PCEP
   extension be activated on authenticated and encrypted sessions across
   PCEs and PCCs belonging to the same administrative authority, using
   Transport Layer Security (TLS) [RFC8253], as per the recommendations
   and best current practices in [RFC7525].

10.  Manageability Considerations

10.1.  Control of Function and Policy

   A PCE or PCC implementation SHOULD allow to configure to enable/
   disable PCECC capability as a global configuration.

10.2.  Information and Data Models

   [RFC7420] describes the PCEP MIB, this MIB can be extended to get the
   PCECC capability status.

   The PCEP YANG module [I-D.ietf-pce-pcep-yang] could be extended to
   enable/disable PCECC capability.

10.3.  Liveness Detection and Monitoring

   Mechanisms defined in this document do not imply any new liveness
   detection and monitoring requirements in addition to those already
   listed in [RFC5440].

10.4.  Verify Correct Operations

   Mechanisms defined in this document do not imply any new operation
   verification requirements in addition to those already listed in
   [RFC5440] and [RFC8231].

10.5.  Requirements On Other Protocols

   PCEP extensions defined in this document do not put new requirements
   on other protocols.




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10.6.  Impact On Network Operations

   PCEP extensions defined in this document do not put new requirements
   on network operations.

11.  IANA Considerations

11.1.  PCEP TLV Type Indicators

   IANA is requested to allocate the following TLV Type Indicator values
   within the "PCEP TLV Type Indicators" sub- registry of the PCEP
   Numbers registry:

        Value          Meaning                        Reference
        TBD14          IPV4-ADDRESS TLV               This document
        TBD15          IPV6-ADDRESS TLV               This document
        TBD16          UNNUMBERED-IPV4-ID-ADDRESS TLV This document
        TBD17          LINKLOCAL-IPV6-ID-ADDRESS TLV  This document

11.2.  PATH-SETUP-TYPE-CAPABILITY Sub-TLV Type Indicators

   [RFC8408] requested the creation of "PATH-SETUP- TYPE-CAPABILITY Sub-
   TLV Type Indicators" sub-registry.  Further IANA is requested to
   allocate the following code-point:

            Value          Meaning               Reference
            TBD12          PCECC-CAPABILITY      This document

11.3.  PCECC-CAPABILITY sub-TLV's Flag field

   This document defines the PCECC-CAPABILITY sub-TLV and requests that
   IANA to create a new sub-registry to manage the value of the PCECC-
   CAPABILITY sub-TLV's 32-bits Flag field.  New values are to be
   assigned by Standards Action [RFC8126].  Each bit should be tracked
   with the following qualities:

   o  Bit number (counting from bit 0 as the most significant bit)

   o  Capability description

   o  Defining RFC

   Currently, there are no allocations in this registry.

            Bit            Name                  Reference
            0-31           Unassigned            This document





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11.4.  Path Setup Type Registry

   [RFC8408] created a sub-registry within the "Path Computation Element
   Protocol (PCEP) Numbers" registry called "PCEP Path Setup Types".
   IANA is requested to allocate a new code point within this registry,
   as follows:

         Value          Description                 Reference
         TBD1           Traffic engineering path is This document
                        set up using PCECC mode

11.5.  PCEP Object

   IANA is requested to allocate new code-point in the "PCEP Objects"
   sub-registry for the CCI object as follows:

          Object-Class Value Name                  Reference
          TBD13              CCI Object-Type       This document
                             0                     Reserved
                             1                     MPLS Label

11.6.  CCI Object Flag Field

   IANA is requested to create a new sub-registry to manage the Flag
   field of the CCI object called "CCI Object 16-bits Flag Field".  New
   values are to be assigned by Standards Action [RFC8126].  Each bit
   should be tracked with the following qualities:

   o  Bit number (counting from bit 0 as the most significant bit)

   o  Capability description

   o  Defining RFC

   Two bits to be defined for the CCI Object flag field in this document
   as follows:

           Bit            Description             Reference
           0-13           Unassigned              This document
           14             C Bit - PCC allocation  This document
           15             O Bit - Specifies label This document
                          is out-label

11.7.  PCEP-Error Object

   IANA is requested to allocate new error types and error values within
   the "PCEP-ERROR Object Error Types and Values" sub-registry of the
   PCEP Numbers registry for the following errors:



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   Error-Type   Meaning
   ----------   -------
   6            Mandatory Object missing.

                 Error-value = TBD11 :               CCI object missing
   10           Reception of an invalid object.

                 Error-value = TBD2 :                Missing PCECC
                                                     Capability sub-TLV
   19           Invalid operation.

                 Error-value = TBD3 :                Attempted PCECC
                                                     operations when
                                                     PCECC capability
                                                     was not advertised
                 Error-value = TBD4 :                Stateful PCE
                                                     capability was not
                                                     advertised
                 Error-value = TBD8 :                Unknown Label
   TBD5         PCECC failure.

                 Error-value = TBD6 :                Label out of range.
                 Error-value = TBD7 :                Instruction failed.
                 Error-value = TBD9 :                Invalid CCI.
                 Error-value = TBD10 :               Unable to allocate
                                                     the specified CCI.

12.  Acknowledgments

   We would like to thank Robert Tao, Changjing Yan, Tieying Huang,
   Avantika, and Aijun Wang for their useful comments and suggestions.

13.  References

13.1.  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>.

   [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>.






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   [RFC5511]  Farrel, A., "Routing Backus-Naur Form (RBNF): A Syntax
              Used to Form Encoding Rules in Various Routing Protocol
              Specifications", RFC 5511, DOI 10.17487/RFC5511, April
              2009, <https://www.rfc-editor.org/info/rfc5511>.

   [RFC7420]  Koushik, A., Stephan, E., Zhao, Q., King, D., and J.
              Hardwick, "Path Computation Element Communication Protocol
              (PCEP) Management Information Base (MIB) Module",
              RFC 7420, DOI 10.17487/RFC7420, December 2014,
              <https://www.rfc-editor.org/info/rfc7420>.

   [RFC7525]  Sheffer, Y., Holz, R., and P. Saint-Andre,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
              2015, <https://www.rfc-editor.org/info/rfc7525>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [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>.

   [RFC8233]  Dhody, D., Wu, Q., Manral, V., Ali, Z., and K. Kumaki,
              "Extensions to the Path Computation Element Communication
              Protocol (PCEP) to Compute Service-Aware Label Switched
              Paths (LSPs)", RFC 8233, DOI 10.17487/RFC8233, September
              2017, <https://www.rfc-editor.org/info/rfc8233>.

   [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>.

   [RFC8408]  Sivabalan, S., Tantsura, J., Minei, I., Varga, R., and J.
              Hardwick, "Conveying Path Setup Type in PCE Communication
              Protocol (PCEP) Messages", RFC 8408, DOI 10.17487/RFC8408,
              July 2018, <https://www.rfc-editor.org/info/rfc8408>.



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13.2.  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>.

   [RFC7025]  Otani, T., Ogaki, K., Caviglia, D., Zhang, F., and C.
              Margaria, "Requirements for GMPLS Applications of PCE",
              RFC 7025, DOI 10.17487/RFC7025, September 2013,
              <https://www.rfc-editor.org/info/rfc7025>.

   [RFC7399]  Farrel, A. and D. King, "Unanswered Questions in the Path
              Computation Element Architecture", RFC 7399,
              DOI 10.17487/RFC7399, October 2014,
              <https://www.rfc-editor.org/info/rfc7399>.

   [RFC7491]  King, D. and A. Farrel, "A PCE-Based Architecture for
              Application-Based Network Operations", RFC 7491,
              DOI 10.17487/RFC7491, March 2015,
              <https://www.rfc-editor.org/info/rfc7491>.

   [RFC7942]  Sheffer, Y. and A. Farrel, "Improving Awareness of Running
              Code: The Implementation Status Section", BCP 205,
              RFC 7942, DOI 10.17487/RFC7942, July 2016,
              <https://www.rfc-editor.org/info/rfc7942>.

   [RFC8253]  Lopez, D., Gonzalez de Dios, O., Wu, Q., and D. Dhody,
              "PCEPS: Usage of TLS to Provide a Secure Transport for the
              Path Computation Element Communication Protocol (PCEP)",
              RFC 8253, DOI 10.17487/RFC8253, October 2017,
              <https://www.rfc-editor.org/info/rfc8253>.

   [RFC8283]  Farrel, A., Ed., Zhao, Q., Ed., Li, Z., and C. Zhou, "An
              Architecture for Use of PCE and the PCE Communication
              Protocol (PCEP) in a Network with Central Control",
              RFC 8283, DOI 10.17487/RFC8283, December 2017,
              <https://www.rfc-editor.org/info/rfc8283>.

   [I-D.ietf-teas-pcecc-use-cases]
              Zhao, Q., Li, Z., Khasanov, B., Dhody, D., Ke, Z., Fang,
              L., Zhou, C., Communications, T., Rachitskiy, A., and A.
              Gulida, "The Use Cases for Path Computation Element (PCE)
              as a Central Controller (PCECC).", draft-ietf-teas-pcecc-
              use-cases-05 (work in progress), March 2020.






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   [I-D.ietf-pce-pcep-yang]
              Dhody, D., Hardwick, J., Beeram, V., and J. Tantsura, "A
              YANG Data Model for Path Computation Element
              Communications Protocol (PCEP)", draft-ietf-pce-pcep-
              yang-14 (work in progress), July 2020.

   [I-D.zhao-pce-pcep-extension-pce-controller-sr]
              Li, Z., Peng, S., Negi, M., Zhao, Q., and C. Zhou, "PCEP
              Procedures and Protocol Extensions for Using PCE as a
              Central Controller (PCECC) of SR-LSPs", draft-zhao-pce-
              pcep-extension-pce-controller-sr-07 (work in progress),
              July 2020.

   [I-D.dhody-pce-pcep-extension-pce-controller-srv6]
              Li, Z., Peng, S., Geng, X., and M. Negi, "PCEP Procedures
              and Protocol Extensions for Using PCE as a Central
              Controller (PCECC) for SRv6", draft-dhody-pce-pcep-
              extension-pce-controller-srv6-04 (work in progress), July
              2020.

   [I-D.li-pce-controlled-id-space]
              Li, C., Chen, M., Wang, A., Cheng, W., and C. Zhou, "PCE
              Controlled ID Space", draft-li-pce-controlled-id-space-06
              (work in progress), July 2020.

   [I-D.ietf-pce-binding-label-sid]
              Filsfils, C., Sivabalan, S., Tantsura, J., Hardwick, J.,
              Previdi, S., and C. Li, "Carrying Binding Label/Segment-ID
              in PCE-based Networks.", draft-ietf-pce-binding-label-
              sid-03 (work in progress), June 2020.

   [I-D.ietf-pce-sr-path-segment]
              Li, C., Chen, M., Cheng, W., Gandhi, R., and Q. Xiong,
              "Path Computation Element Communication Protocol (PCEP)
              Extension for Path Segment in Segment Routing (SR)",
              draft-ietf-pce-sr-path-segment-01 (work in progress), May
              2020.














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Appendix A.  Contributor Addresses

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

   EMail: dhruv.ietf@gmail.com

   Satish Karunanithi
   Huawei Technologies
   Divyashree Techno Park, Whitefield
   Bangalore, Karnataka  560066
   India

   EMail: satishk@huawei.com

   Adrian Farrel
   Old Dog Consulting
   UK

   EMail: adrian@olddog.co.uk

   Xuesong Geng
   Huawei Technologies
   China

   Email: gengxuesong@huawei.com

   Udayasree Palle

   EMail: udayasreereddy@gmail.com

   Katherine Zhao
   Futurewei Technologies

   EMail: katherine.zhao@futurewei.com

   Boris Zhang
   Telus Ltd.
   Toronto
   Canada

   EMail: boris.zhang@telus.com

   Alex Tokar
   Cisco Systems



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   Slovak Republic

   EMail: atokar@cisco.com


Authors' Addresses

   Zhenbin Li
   Huawei Technologies
   Huawei Bld., No.156 Beiqing Rd.
   Beijing    100095
   China

   EMail: lizhenbin@huawei.com


   Shuping Peng
   Huawei Technologies
   Huawei Bld., No.156 Beiqing Rd.
   Beijing  100095
   China

   EMail: pengshuping@huawei.com


   Mahendra Singh Negi
   RtBrick India
   N-17L, Floor-1, 18th Cross Rd, HSR Layout Sector-3
   Bangalore, Karnataka  560102
   India

   EMail: mahend.ietf@gmail.com


   Quintin Zhao
   Etheric Networks
   1009 S CLAREMONT ST
   SAN MATEO, CA  94402
   USA

   EMail: qzhao@ethericnetworks.com


   Chao Zhou
   HPE

   EMail: chaozhou_us@yahoo.com




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