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PCE Working Group                                                M. Negi
Internet-Draft                                                     Z. Li
Intended status: Standards Track                                 X. Geng
Expires: February 23, 2020                           Huawei Technologies
                                                         August 22, 2019


   PCEP Procedures and Protocol Extensions for Using PCE as a Central
                      Controller (PCECC) for SRv6
         draft-dhody-pce-pcep-extension-pce-controller-srv6-02

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 (G)MPLS 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.  This document specifies
   the procedures and PCEP protocol extensions when a PCE-based
   controller is also responsible for configuring the forwarding actions
   on the routers for Segment Routing in IPv6 (SRv6), in addition to
   computing the SRv6 paths for packet flows and telling the edge
   routers what instructions to attach to packets as they enter the
   network.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.





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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on February 23, 2020.

Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   5
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  PCECC SRv6  . . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  PCEP Requirements . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Procedures for Using the PCE as the Central Controller
       (PCECC) in SRv6 . . . . . . . . . . . . . . . . . . . . . . .   6
     5.1.  Stateful PCE Model  . . . . . . . . . . . . . . . . . . .   6
     5.2.  New Functions . . . . . . . . . . . . . . . . . . . . . .   6
     5.3.  PCECC Capability Advertisement  . . . . . . . . . . . . .   7
     5.4.  PCEP session IP address and TEDB Router ID  . . . . . . .   7
     5.5.  SRv6 Path Operations  . . . . . . . . . . . . . . . . . .   7
       5.5.1.  PCECC Segment Routing in IPv6 (SRv6)  . . . . . . . .   7
         5.5.1.1.  PCECC SRv6 Node/Prefix SID allocation . . . . . .   7
         5.5.1.2.  PCECC SRv6 Adjacency SID allocation . . . . . . .   8
         5.5.1.3.  Redundant PCEs  . . . . . . . . . . . . . . . . .   9
         5.5.1.4.  Re Delegation and Cleanup . . . . . . . . . . . .   9
         5.5.1.5.  Synchronization of SRv6 SID Allocations . . . . .   9
   6.  PCEP messages . . . . . . . . . . . . . . . . . . . . . . . .   9
   7.  PCEP Objects  . . . . . . . . . . . . . . . . . . . . . . . .   9
     7.1.  OPEN Object . . . . . . . . . . . . . . . . . . . . . . .   9
       7.1.1.  PCECC Capability sub-TLV  . . . . . . . . . . . . . .   9
     7.2.  PATH-SETUP-TYPE TLV . . . . . . . . . . . . . . . . . . .  10
     7.3.  CCI Object  . . . . . . . . . . . . . . . . . . . . . . .  10



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     7.4.  FEC Object  . . . . . . . . . . . . . . . . . . . . . . .  11
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   9.  Manageability Considerations  . . . . . . . . . . . . . . . .  11
     9.1.  Control of Function and Policy  . . . . . . . . . . . . .  11
     9.2.  Information and Data Models . . . . . . . . . . . . . . .  11
     9.3.  Liveness Detection and Monitoring . . . . . . . . . . . .  12
     9.4.  Verify Correct Operations . . . . . . . . . . . . . . . .  12
     9.5.  Requirements On Other Protocols . . . . . . . . . . . . .  12
     9.6.  Impact On Network Operations  . . . . . . . . . . . . . .  12
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
     10.1.  PCECC-CAPABILITY TLV . . . . . . . . . . . . . . . . . .  12
     10.2.  New Path Setup Type Registry . . . . . . . . . . . . . .  12
     10.3.  PCEP-Error Object  . . . . . . . . . . . . . . . . . . .  13
   11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  13
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  13
     12.2.  Informative References . . . . . . . . . . . . . . . . .  14
   Appendix A.  Contributor Addresses  . . . . . . . . . . . . . . .  17
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  17

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].

   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].



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   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.

   [I-D.ietf-pce-pcep-extension-for-pce-controller] specify 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.

   Segment Routing (SR) technology leverages the source routing and
   tunneling paradigms.  A source node can choose a path without relying
   on hop-by-hop signaling protocols such as LDP or RSVP-TE.  Each path
   is specified as a set of "segments" advertised by link-state routing
   protocols (IS-IS or OSPF).  [RFC8402] provides an introduction to SR
   architecture.  The corresponding IS-IS and OSPF extensions are
   specified in [I-D.ietf-isis-segment-routing-extensions] and
   [I-D.ietf-ospf-segment-routing-extensions] , respectively.  It relies
   on a series of forwarding instructions being placed in the header of
   a packet.  The list of segment forming the path is called the Segment
   List and is encoded in the packet header.  Segment Routing can be
   applied to the IPv6 architecture with the Segment Routing Header
   (SRH) [I-D.ietf-6man-segment-routing-header].  A segment is encoded
   as an IPv6 address.  An ordered list of segments is encoded as an
   ordered list of IPv6 addresses in the routing header.  The active
   segment is indicated by the Destination Address of the packet.  Upon
   completion of a segment, a pointer in the new routing header is
   incremented and indicates the next segment.  The segment routing
   architecture supports operations that can be used to steer packet
   flows in a network, thus providing a form of traffic engineering.
   [I-D.ietf-pce-segment-routing] and
   [I-D.ietf-pce-segment-routing-ipv6] specify the SR specific PCEP
   extensions.

   PCECC may further use PCEP protocol for SR SID (Segment Identifier)
   distribution on the SR nodes with some benefits.
   [I-D.zhao-pce-pcep-extension-pce-controller-sr] specifies the
   procedures and PCEP protocol extensions when a PCE-based controller
   is also responsible for configuring the forwarding actions on the
   routers (SR SID distribution in this case), in addition to computing
   the paths for packet flows in a segment routing network and telling



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   the edge routers what instructions to attach to packets as they enter
   the network.  This document extends this to include SRv6 SID
   distribution as well.

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

   Terminologies used in this document is same as described in the draft
   [RFC8283] and [I-D.ietf-teas-pcecc-use-cases].

3.  PCECC SRv6

   [I-D.ietf-pce-segment-routing] specifies extensions to PCEP that
   allow a stateful PCE to compute, update or initiate SR-TE paths for
   MPLS dataplane.  An ingress node of an SR-TE path appends all
   outgoing packets with a list of MPLS labels (SIDs).  This is encoded
   in SR-ERO subobject, capable of carrying a label (SID) as well as the
   identity of the node/adjacency label (SID).
   [I-D.ietf-pce-segment-routing-ipv6] extends the procedure to include
   support for SRv6 paths.

   As per [I-D.ietf-6man-segment-routing-header], an SRv6 Segment is a
   128-bit value.  "SRv6 SID" or simply "SID" are often used as a
   shorter reference for "SRv6 Segment".  Further details are in an
   illustration provided in [I-D.ietf-spring-srv6-network-programming].
   The SR is applied to IPV6 forwarding plane using SRH.  A SR path can
   be derived from an IGP Shortest Path Tree (SPT), but SR-TE paths may
   not follow IGP SPT.  Such paths may be chosen by a suitable network
   planning tool, or a PCE and provisioned on the ingress node.
   [I-D.ietf-pce-segment-routing-ipv6] extended SR-ERO subobject capable
   of carrying an SRv6 SID as well as the identity of the node/adjacency
   represented by the SID.

   As per [RFC8283], PCE as a central controller can allocate and
   provision the node/prefix/adjacency label (SID) via PCEP.  As per
   [I-D.ietf-teas-pcecc-use-cases] this is also applicable to SRv6 SIDs.

   Rest of the processing is similar to existing stateful PCE with SRv6
   mechanism.





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4.  PCEP Requirements

   Following key requirements for PCECC-SRv6 should be considered when`
   designing the PCECC based solution:

   o  PCEP speaker supporting this draft MUST have the capability to
      advertise its PCECC-SRv6 capability to its peers.

   o  PCEP speaker not supporting this draft MUST be able to reject
      PCECC-SRv6 related message with a reason code that indicates no
      support for it.

   o  PCEP procedures MUST provide a means to update (or cleanup) the
      SRv6 SID to the PCC.

   o  PCEP procedures SHOULD provide a means to synchronize the SRv6 SID
      allocations between PCE to PCC in the PCEP messages.

5.  Procedures for Using the PCE as the Central Controller (PCECC) in
    SRv6

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 Functions

   This document uses the same PCEP messages and its extensions which
   are described in [I-D.ietf-pce-pcep-extension-for-pce-controller] and
   [I-D.zhao-pce-pcep-extension-pce-controller-sr] for PCECC-SRv6 as
   well.

   PCEP messages PCRpt, PCInitiate, PCUpd are also used to send LSP
   Reports, LSP setup and LSP update respectively.  The extended
   PCInitiate message described in
   [I-D.ietf-pce-pcep-extension-for-pce-controller] is used to download
   or cleanup central controller's instructions (CCIs) (SRv6 SID in
   scope of this document).  The extended PCRpt message described in
   [I-D.ietf-pce-pcep-extension-for-pce-controller] is also used to
   report the CCIs (SRv6 SIDs) from PCC to PCE.

   [I-D.ietf-pce-pcep-extension-for-pce-controller] specify an object
   called CCI for the encoding of central controller's instructions.
   [I-D.zhao-pce-pcep-extension-pce-controller-sr] extends the CCI by
   defining a object-type for segment routing.  This document further
   extends the CCI by defining another object-type for SRv6.



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5.3.  PCECC Capability Advertisement

   During PCEP Initialization Phase, PCEP Speakers (PCE or PCC)
   advertise their support of PCECC extensions.  A PCEP Speaker includes
   the "PCECC Capability" sub-TLV, described in
   [I-D.ietf-pce-pcep-extension-for-pce-controller].

   A S-bit is added in PCECC-CAPABILITY sub-TLV to indicate support for
   PCECC-SR in [I-D.zhao-pce-pcep-extension-pce-controller-sr].  This
   document adds another I-bit to indicate support for SR in IPv6.  A
   PCC MUST set I-bit in PCECC-CAPABILITY sub-TLV and include SRv6-PCE-
   CAPABILITY sub-TLV ([I-D.ietf-pce-segment-routing-ipv6]) in OPEN
   Object (inside the the PATH-SETUP-TYPE-CAPABILITY TLV) to support the
   PCECC SRv6 extensions defined in this document.  If I-bit is set in
   PCECC-CAPABILITY sub-TLV and SRv6-PCE-CAPABILITY sub-TLV is not
   advertised in OPEN Object, PCE SHOULD send a PCErr message with
   Error-Type=19 (Invalid Operation) and Error-value=TBD(SRv6 capability
   was not advertised) and terminate the session.

5.4.  PCEP session IP address and TEDB Router ID

   As described in [I-D.zhao-pce-pcep-extension-pce-controller-sr], it
   is important to link the session IP address with the Router ID in
   TEDB for successful PCECC operations.

5.5.  SRv6 Path Operations

   The PCEP messages pertaining to PCECC-SRv6 MUST include PATH-SETUP-
   TYPE TLV [RFC8408] with PST=TBD in the SRP object to clearly identify
   the PCECC-SRv6 setup is intended.

5.5.1.  PCECC Segment Routing in IPv6 (SRv6)

   Segment Routing (SR) as described in [RFC8402] depends on "segments"
   that are advertised by Interior Gateway Protocols (IGPs).  The SR-
   node allocates and advertises the SID (node, adj etc) and flood via
   the IGP.  This document proposes a new mechanism where PCE allocates
   the SRv6 SID centrally and uses PCEP to advertise the SRv6 SID.  In
   some deployments PCE (and PCEP) are better suited than IGP because of
   centralized nature of PCE and direct TCP based PCEP session to the
   node.

5.5.1.1.  PCECC SRv6 Node/Prefix SID allocation

   Each node (PCC) is allocated a node SRv6 SID by the PCECC.  The PCECC
   sends PCInitiate message to update the SID table of each node.  The
   TE router ID is determined from the TEDB or from "IPv4/IPv6 Router-
   ID" Sub-TLV [I-D.dhodylee-pce-pcep-ls], in the OPEN Object.



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   On receiving the SRv6 node SID allocation, each node (PCC) uses the
   local routing information to determine the next-hop and download the
   forwarding instructions accordingly.  The PCInitiate message in this
   case MUST have FEC object.

   On receiving the SRv6 node SID allocation:

      For the local SID, node (PCC) needs to update SID with associated
      function (END function in this case) in "My Local SID Table"
      ([I-D.ietf-spring-srv6-network-programming]).

      For the non-local SID, node (PCC) uses the local routing
      information to determine the next-hop and download the forwarding
      instructions accordingly.

   The PCInitiate message in this case MUST have FEC object.

   The forwarding behavior and the end result is similar to IGP based
   "Node-SID" in SRv6.  Thus, from anywhere in the domain, it enforces
   the ECMP-aware shortest-path forwarding of the packet towards the
   related node.

   PCE relies on the Node/Prefix SRv6 SID cleanup using the same
   PCInitiate message.

5.5.1.2.  PCECC SRv6 Adjacency SID allocation

   [I-D.ietf-pce-segment-routing] extends PCEP to allow a stateful PCE
   to compute and initiate SR-TE paths, as well as a PCC to request a
   path subject to certain constraint(s) and optimization criteria in SR
   networks.

   For PCECC SR, apart from node-SID, Adj-SID is used where each
   adjacency is allocated an Adj-SID by the PCECC.  The PCECC sends
   PCInitiate message to update the label map of each Adj to the
   corresponding nodes in the domain.  Each node (PCC) download the SRv6
   SID instructions accordingly.  Similar to SRv6 Node/Prefix Label
   allocation, the PCInitiate message in this case uses the FEC object.

   The forwarding behavior and the end result is similar to IGP based
   "Adj-SID" in SRv6.

   The Path Setup Type for segment routing MUST be set for PCECC SRv6 =
   TBD (see Section 7.2).  All PCEP procedures and mechanism are similar
   to [I-D.ietf-pce-segment-routing].

   PCE relies on the Adj label cleanup using the same PCInitiate
   message.



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5.5.1.3.  Redundant PCEs

   [I-D.litkowski-pce-state-sync] describes synchronization mechanism
   between the stateful PCEs.  The SRv6 SIDs allocated by a PCE MUST
   also be synchronized among PCEs for PCECC SRv6 state synchronization.
   Note that the SRv6 SIDs are independent to the PCECC-SRv6 paths, and
   remains intact till any topology change.  The redundant PCEs MUST
   have a common view of all SRv6 SIDs allocated in the domain.

5.5.1.4.  Re Delegation and Cleanup

   [I-D.ietf-pce-pcep-extension-for-pce-controller] describes the action
   needed for CCIs for the Basic PCECC LSP on this terminated session.
   Similarly actions should be applied for the SRv6 SID as well.

5.5.1.5.  Synchronization of SRv6 SID Allocations

   [I-D.ietf-pce-pcep-extension-for-pce-controller] describes the
   synchronization of Central Controller's Instructions (CCI) via LSP
   state synchronization as described in [RFC8231] and [RFC8232].  Same
   procedures should be applied for SRv6 SIDs as well.

6.  PCEP messages

   The PCEP message is as per
   [I-D.zhao-pce-pcep-extension-pce-controller-sr].

7.  PCEP Objects

7.1.  OPEN Object

7.1.1.  PCECC Capability sub-TLV

   [I-D.ietf-pce-pcep-extension-for-pce-controller] defined the PCECC-
   CAPABILITY TLV.

   A new I-bit is defined in PCECC-CAPABILITY sub-TLV for PCECC-SRv6:


       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=TBD        |            Length=4           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             Flags                         |I|S|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+





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   I (PCECC-SRv6-CAPABILITY - 1 bit): If set to 1 by a PCEP speaker, it
   indicates that the PCEP speaker is capable for PCECC-SRv6 capability
   and PCE would allocate node and Adj SRv6 SID on this session.

7.2.  PATH-SETUP-TYPE TLV

   The PATH-SETUP-TYPE TLV is defined in [RFC8408].  PST = TBD is used
   when Path is setup via PCECC SRv6 mode.

   On a PCRpt/PCUpd/PCInitiate message, the PST=TBD indicates that this
   path was setup via a PCECC-SRv6 based mechanism where either the SIDs
   were allocated/instructed by PCE via PCECC mechanism.

7.3.  CCI Object

   The Central Control Instructions (CCI) Object is used by the PCE to
   specify the forwarding instructions is defined in
   [I-D.ietf-pce-pcep-extension-for-pce-controller].  This document
   defines another object-type for SRv6 purpose.

   CCI Object-Type is TBD for SRv6 as below -


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            CC-ID                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      MT-ID    |    Algorithm  |        Flags        |N|E|V|L|O|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Reserved            |   SRv6 Endpoint Function      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                      SRv6 Identifier                          |
   |                         (128-bit)                             |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                        Optional TLV                         //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   The field CC-ID is as described in
   [I-D.ietf-pce-pcep-extension-for-pce-controller].  The field MT-ID,
   Algorithm, Flags are defined in
   [I-D.zhao-pce-pcep-extension-pce-controller-sr].




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   Reserved: MUST be set to 0 while sending and ignored on receipt.

   SRv6 Endpoint Function: 16 bit field representing supported functions
   associated with SRv6 SIDs.

   SRv6 Identifier: 128 bit IPv6 addresses representing SRv6 segment.

   [Editor's Note - It might be useful to seperate the LOC:FUNC part in
   the SRv6 SID]

7.4.  FEC Object

   The FEC Object is used to specify the FEC information and MAY be
   carried within PCInitiate or PCRpt message.

   FEC Object (and various Object-Types) are described in
   [I-D.zhao-pce-pcep-extension-pce-controller-sr].  SRv6 Node SID MUST
   includes the FEC Object-Type 2 for IPv6 Node.  SRv6 Adjacency SID
   MUST include the FEC Object-Type=4 for IPv6 adjacency.  Further FEC
   object types would be added in future revisions.

8.  Security Considerations

   The security considerations described in
   [I-D.ietf-pce-pcep-extension-for-pce-controller] apply to the
   extensions described in this document.

   As per [RFC8231], it is RECOMMENDED that these PCEP extensions only
   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] (unless explicitly set aside in
   [RFC8253]).

9.  Manageability Considerations

9.1.  Control of Function and Policy

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

9.2.  Information and Data Models

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

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



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9.3.  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].

9.4.  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].

9.5.  Requirements On Other Protocols

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

9.6.  Impact On Network Operations

   PCEP implementation SHOULD allow a limit to be placed on the rate of
   PCInitiate/PCUpd messages (as per [RFC8231]) sent by PCE and
   processed by PCC.  It SHOULD also allow sending a notification when a
   rate threshold is reached.

10.  IANA Considerations

10.1.  PCECC-CAPABILITY TLV

   [I-D.ietf-pce-pcep-extension-for-pce-controller] defines the PCECC-
   CAPABILITY TLV and requests that IANA creates a registry to manage
   the value of the PCECC-CAPABILITY TLV's Flag field.  IANA is
   requested to allocate a new bit in the PCECC-CAPABILITY TLV Flag
   Field registry, as follows:

          Bit            Description                Reference
          TBD            I((PCECC-SRv6-CAPABILITY)) This document

10.2.  New Path Setup Type Registry

   IANA is requested to allocate new PST Field in PATH- SETUP-TYPE TLV.
   The allocation policy for this new registry should be by IETF
   Consensus.  The new registry should contain the following value:

         Value          Description                 Reference
         TBD            Path is                     This document
                        setup using PCECC-SRv6 mode





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10.3.  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:


   Error-Type   Meaning
   ----------   -------
   19           Invalid operation.

                 Error-value = TBD :                 SRv6 capability was
                                                     not advertised

11.  Acknowledgments

12.  References

12.1.  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>.

   [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>.

   [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>.






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   [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>.

   [I-D.ietf-pce-segment-routing-ipv6]
              Negi, M., Li, C., Sivabalan, S., Kaladharan, P., and Y.
              Zhu, "PCEP Extensions for Segment Routing leveraging the
              IPv6 data plane", draft-ietf-pce-segment-routing-ipv6-02
              (work in progress), April 2019.

   [I-D.ietf-pce-pcep-extension-for-pce-controller]
              Zhao, Q., Li, Z., Negi, M., and C. Zhou, "PCEP Procedures
              and Protocol Extensions for Using PCE as a Central
              Controller (PCECC) of LSPs", draft-ietf-pce-pcep-
              extension-for-pce-controller-02 (work in progress), July
              2019.

   [I-D.zhao-pce-pcep-extension-pce-controller-sr]
              Zhao, Q., Li, Z., Negi, M., 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-05 (work in progress), July
              2019.

12.2.  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>.




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   [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>.

   [RFC8232]  Crabbe, E., Minei, I., Medved, J., Varga, R., Zhang, X.,
              and D. Dhody, "Optimizations of Label Switched Path State
              Synchronization Procedures for a Stateful PCE", RFC 8232,
              DOI 10.17487/RFC8232, September 2017,
              <https://www.rfc-editor.org/info/rfc8232>.

   [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>.

   [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>.

   [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>.

   [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-04 (work in progress), July 2019.

   [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-12 (work in progress), July 2019.





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   [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-isis-segment-routing-extensions]
              Previdi, S., Ginsberg, L., Filsfils, C., Bashandy, A.,
              Gredler, H., and B. Decraene, "IS-IS Extensions for
              Segment Routing", draft-ietf-isis-segment-routing-
              extensions-25 (work in progress), May 2019.

   [I-D.ietf-ospf-segment-routing-extensions]
              Psenak, P., Previdi, S., Filsfils, C., Gredler, H.,
              Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
              Extensions for Segment Routing", draft-ietf-ospf-segment-
              routing-extensions-27 (work in progress), December 2018.

   [I-D.litkowski-pce-state-sync]
              Litkowski, S., Sivabalan, S., Li, C., and H. Zheng, "Inter
              Stateful Path Computation Element (PCE) Communication
              Procedures.", draft-litkowski-pce-state-sync-06 (work in
              progress), July 2019.

   [I-D.dhodylee-pce-pcep-ls]
              Dhody, D., Lee, Y., and D. Ceccarelli, "PCEP Extension for
              Distribution of Link-State and TE Information.", draft-
              dhodylee-pce-pcep-ls-13 (work in progress), February 2019.

   [I-D.ietf-spring-srv6-network-programming]
              Filsfils, C., Camarillo, P., Leddy, J.,
              daniel.voyer@bell.ca, d., Matsushima, S., and Z. Li, "SRv6
              Network Programming", draft-ietf-spring-srv6-network-
              programming-01 (work in progress), July 2019.

   [I-D.ietf-6man-segment-routing-header]
              Filsfils, C., Dukes, D., Previdi, S., Leddy, J.,
              Matsushima, S., and d. daniel.voyer@bell.ca, "IPv6 Segment
              Routing Header (SRH)", draft-ietf-6man-segment-routing-
              header-22 (work in progress), August 2019.











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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



Authors' Addresses

   Mahendra Singh Negi
   Huawei Technologies
   Divyashree Techno Park, Whitefield
   Bangalore, Karnataka  560066
   India

   EMail: mahend.ietf@gmail.com


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

   EMail: lizhenbin@huawei.com


   Xuesong Geng
   Huawei Technologies
   China

   EMail: gengxuesong@huawei.com












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