



Network Working Group                                           D. Dhody
Internet-Draft                                       Huawei Technologies
Intended status: Standards Track                               A. Farrel
Expires: May 3, 2021                                  Old Dog Consulting
                                                                   Z. Li
                                                     Huawei Technologies
                                                        October 30, 2020


                 PCEP Extension for Flow Specification
                    draft-ietf-pce-pcep-flowspec-12

Abstract

   The Path Computation Element (PCE) is a functional component capable
   of selecting paths through a traffic engineering network.  These
   paths may be supplied in response to requests for computation, or may
   be unsolicited requests issued by the PCE to network elements.  Both
   approaches use the PCE Communication Protocol (PCEP) to convey the
   details of the computed path.

   Traffic flows may be categorized and described using "Flow
   Specifications".  RFC XXXX defines the Flow Specification and
   describes how Flow Specification Components are used to describe
   traffic flows.  RFC XXXX also defines how Flow Specifications may be
   distributed in BGP to allow specific traffic flows to be associated
   with routes.

   This document specifies a set of extensions to PCEP to support
   dissemination of Flow Specifications.  This allows a PCE to indicate
   what traffic should be placed on each path that it is aware of.

   The extensions defined in this document include the creation, update,
   and withdrawal of Flow Specifications via PCEP, and can be applied to
   tunnels initiated by the PCE or to tunnels where control is delegated
   to the PCE by the PCC.  Furthermore, a PCC requesting a new path can
   include Flow Specifications in the request to indicate the purpose of
   the tunnel allowing the PCE to factor this into the path computation.

   RFC Editor Note: Please replace XXXX in the Abstract with the RFC
   number assigned to draft-ietf-idr-rfc5575bis when it is published.
   Please remove this note.

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

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Procedures for PCE Use of Flow Specifications . . . . . . . .   6
     3.1.  Context for PCE Use of Flow Specifications  . . . . . . .   6
     3.2.  Elements of Procedure . . . . . . . . . . . . . . . . . .   7
       3.2.1.  Capability Advertisement  . . . . . . . . . . . . . .   7
       3.2.2.  Dissemination Procedures  . . . . . . . . . . . . . .   8
       3.2.3.  Flow Specification Synchronization  . . . . . . . . .   9
   4.  PCE FlowSpec Capability TLV . . . . . . . . . . . . . . . . .  10
   5.  PCEP FLOWSPEC Object  . . . . . . . . . . . . . . . . . . . .  10
   6.  Flow Filter TLV and L2 Flow Filter TLV  . . . . . . . . . . .  13
   7.  Flow Specification TLVs . . . . . . . . . . . . . . . . . . .  13
     7.1.  L2 Flow Specification TLVs  . . . . . . . . . . . . . . .  17
   8.  Detailed Procedures . . . . . . . . . . . . . . . . . . . . .  18
     8.1.  Default Behavior and Backward Compatibility . . . . . . .  18
     8.2.  Composite Flow Specifications . . . . . . . . . . . . . .  19
     8.3.  Modifying Flow Specifications . . . . . . . . . . . . . .  19
     8.4.  Multiple Flow Specifications  . . . . . . . . . . . . . .  19
     8.5.  Adding and Removing Flow Specifications . . . . . . . . .  20



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     8.6.  VPN Identifiers . . . . . . . . . . . . . . . . . . . . .  20
     8.7.  Priorities and Overlapping Flow Specifications  . . . . .  20
   9.  PCEP Messages . . . . . . . . . . . . . . . . . . . . . . . .  21
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  24
     10.1.  PCEP Objects . . . . . . . . . . . . . . . . . . . . . .  24
       10.1.1.  PCEP FLOWSPEC Object Flag Field  . . . . . . . . . .  24
     10.2.  PCEP TLV Type Indicators . . . . . . . . . . . . . . . .  25
     10.3.  Flow Specification TLV Type Indicators . . . . . . . . .  25
     10.4.  L2 Flow Specification TLV Type Indicators  . . . . . . .  26
     10.5.  PCEP Error Codes . . . . . . . . . . . . . . . . . . . .  27
     10.6.  PCE Capability Flag  . . . . . . . . . . . . . . . . . .  27
   11. Implementation Status . . . . . . . . . . . . . . . . . . . .  27
   12. Security Considerations . . . . . . . . . . . . . . . . . . .  28
   13. Manageability Considerations  . . . . . . . . . . . . . . . .  29
     13.1.  Management of Multiple Flow Specifications . . . . . . .  29
     13.2.  Control of Function through Configuration and Policy . .  30
     13.3.  Information and Data Models  . . . . . . . . . . . . . .  30
     13.4.  Liveness Detection and Monitoring  . . . . . . . . . . .  31
     13.5.  Verifying Correct Operation  . . . . . . . . . . . . . .  31
     13.6.  Requirements on Other Protocols and Functional
            Components . . . . . . . . . . . . . . . . . . . . . . .  31
     13.7.  Impact on Network Operation  . . . . . . . . . . . . . .  31
   14. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  31
   15. References  . . . . . . . . . . . . . . . . . . . . . . . . .  31
     15.1.  Normative References . . . . . . . . . . . . . . . . . .  32
     15.2.  Informative References . . . . . . . . . . . . . . . . .  33
   Appendix A.  Contributors . . . . . . . . . . . . . . . . . . . .  35
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  36

1.  Introduction

   [RFC4655] defines the Path Computation Element (PCE), a functional
   component capable of computing paths for use in traffic engineering
   networks.  PCE was originally conceived for use in Multiprotocol
   Label Switching (MPLS) for Traffic Engineering (TE) networks to
   derive the routes of Label Switched Paths (LSPs).  However, the scope
   of PCE was quickly extended to make it applicable to Generalized MPLS
   (GMPLS)-controlled networks, and more recent work has brought other
   traffic engineering technologies and planning applications into scope
   (for example, Segment Routing (SR) [RFC8664]).

   [RFC5440] describes the Path Computation Element Communication
   Protocol (PCEP).  PCEP defines the communication between a Path
   Computation Client (PCC) and a PCE, or between PCE and PCE, enabling
   computation of path for MPLS-TE LSPs.

   Stateful PCE [RFC8231] specifies a set of extensions to PCEP to
   enable control of TE-LSPs by a PCE that retains state about the LSPs



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   provisioned in the network (a stateful PCE).  [RFC8281] describes the
   setup, maintenance, and teardown of LSPs initiated by a stateful PCE
   without the need for local configuration on the PCC, thus allowing
   for a dynamic network that is centrally controlled.  [RFC8283]
   introduces the architecture for PCE as a central controller and
   describes how PCE can be viewed as a component that performs
   computation to place 'flows' within the network and decide how these
   flows are routed.

   The description of traffic flows by the combination of multiple Flow
   Specification Components and their dissemination as traffic flow
   specifications (Flow Specifications) is described for BGP in
   [I-D.ietf-idr-rfc5575bis].  In BGP, a Flow Specification is comprised
   of traffic filtering rules and is associated with actions to perform
   on the packets that match the Flow Specification.  The BGP routers
   that receive a Flow Specification can classify received packets
   according to the traffic filtering rules and can direct packets based
   on the associated actions.

   When a PCE is used to initiate tunnels (such as TE-LSPs or SR paths)
   using PCEP, it is important that the head end of the tunnels
   understands what traffic to place on each tunnel.  The data flows
   intended for a tunnel can be described using Flow Specification
   Components.  When PCEP is in use for tunnel initiation it makes sense
   for that same protocol to be used to distribute the Flow
   Specification Components that describe what data is to flow on those
   tunnels.

   This document specifies a set of extensions to PCEP to support
   dissemination of Flow Specification Components.  We term the
   description of a traffic flow using Flow Specification Components as
   a "Flow Specification".  This term is conceptually the same as the
   term used in [I-D.ietf-idr-rfc5575bis], however, no mechanism is
   provided to distribute an action associated with the Flow
   Specification because there is only one action that is applicable in
   the PCEP context (that is, directing the matching traffic to the
   identified LSP).

   The extensions defined in this document include the creation, update,
   and withdrawal of Flow Specifications via PCEP, and can be applied to
   tunnels initiated by the PCE or to tunnels where control is delegated
   to the PCE by the PCC.  Furthermore, a PCC requesting a new path can
   include Flow Specifications in the request to indicate the purpose of
   the tunnel allowing the PCE to factor this into the path computation.

   Flow Specifications are carried in TLVs within a new object called
   the FLOWSPEC object defined in this document.  The flow filtering




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   rules indicated by the Flow Specifications are mainly defined by BGP
   Flow Specifications.

   Note that PCEP-installed Flow Specifications are intended to be
   installed only at the head-end of the LSP to which they direct
   traffic.  It is acceptable (and potentially desirable) that other
   routers in the network have Flow Specifications installed that match
   the same traffic, but direct it onto different routes or to different
   LSPs.  Those other Flow Specifications may be installed using the
   PCEP extensions defined in this document, may be distributed using
   BGP per [I-D.ietf-idr-rfc5575bis], or may be configured using manual
   operations.  Since this document is about PCEP-installed Flow
   Specifications, those other Flow Specifications at other routers are
   out of scope.  In this context, however, it is worth noting that
   changes to the wider routing system (such as the distribution and
   installation of BGP Flow Specifications, or fluctuations in the IGP
   link state database) might mean that traffic matching the PCEP Flow
   Specification never reaches the head end of the LSP at which the PCEP
   Flow Specification has been installed.  This may or may not be
   desirable according to the operator's traffic engineering and routing
   policies, and is particularly applicable at LSPs that do not have
   their head ends at the ingress-edge of the network, but it is not an
   effect that this document seeks to address.

2.  Terminology

   This document uses the following terms defined in [RFC5440]: PCC,
   PCE, PCEP Peer.

   The following term from [I-D.ietf-idr-rfc5575bis] is used frequently
   throughout this document:

      A Flow Specification is an n-tuple consisting of several matching
      criteria that can be applied to IP traffic.  A given IP packet is
      said to match the defined Flow Specification if it matches all the
      specified criteria.

   [I-D.ietf-idr-rfc5575bis] also states that "A given Flow
   Specification may be associated with a set of attributes," and that,
   "...attributes can be used to encode a set of predetermined actions."
   However, in the context of this document, no action is explicitly
   specified associated with the Flow Specification since the action
   "forward all matching traffic onto the associated path" is implicit.

   How an implementation decides how to filter traffic that matches a
   Flow Specification does not form part of this specification, but a
   flag is provided to indicate whether the sender of a PCEP message




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   that includes a Flow Specification intends it to be installed as a
   Longest Prefix Match route or as a Flow Specification policy.

   This document uses the terms "stateful PCE" and "active PCE" as
   advocated in [RFC7399].

   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.

3.  Procedures for PCE Use of Flow Specifications

3.1.  Context for PCE Use of Flow Specifications

   In the PCE architecture there are five steps in the setup and use of
   LSPs:

   1.  Decide which LSPs to set up.  The decision may be made by a user,
       by a PCC, or by the PCE.  There can be a number of triggers for
       this including user intervention and dynamic response to changes
       in traffic demands.

   2.  Decide what properties to assign to an LSP.  This can include
       bandwidth reservations, priorities, and DSCP (i.e., MPLS Traffic
       Class field).  This function is also determined by user
       configuration or in response to predicted or observed traffic
       demands.

   3.  Decide what traffic to put on the LSP.  This is effectively
       determining which traffic flows to assign to which LSPs, and
       practically, this is closely linked to the first two decisions
       listed above.

   4.  Cause the LSP to be set up and modified to have the right
       characteristics.  This will usually involve the PCE advising or
       instructing the PCC at the head end of the LSP, and the PCC will
       then signal the LSP across the network.

   5.  Tell the head end of the LSP what traffic to put on the LSP.
       This may happen after or at the same time as the LSP is set up.
       This step is the subject of this document.








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3.2.  Elements of Procedure

   There are three elements of procedure:

   o  A PCE and a PCC must be able to indicate whether or not they
      support the use of Flow Specifications.

   o  A PCE or PCC must be able to include Flow Specifications in PCEP
      messages with clear understanding of the applicability of those
      Flow Specifications in each case.  This includes whether the use
      of such information is mandatory, constrained, or optional, and
      how overlapping Flow Specifications will be resolved.

   o  Flow Specification information/state must be synchronized between
      PCEP peers so that, on recovery, the peers have the same
      understanding of which Flow Specifications apply just as is
      required in the case of stateful PCE and LSP delegation (see
      Section 5.6 of [RFC8231]).

   The following subsections describe these points.

3.2.1.  Capability Advertisement

   As with most PCEP capability advertisements, the ability to support
   Flow Specifications can be indicated in the PCEP OPEN message or in
   IGP PCE capability advertisements.

3.2.1.1.  PCEP OPEN Message

   During PCEP session establishment, a PCC or PCE that supports the
   procedures described in this document announces this fact by
   including the "PCE FlowSpec Capability" TLV (described in Section 4)
   in the OPEN Object carried in the PCEP Open message.

   The presence of the PCE FlowSpec Capability TLV in the OPEN Object in
   a PCE's OPEN message indicates that the PCE can distribute FlowSpecs
   to PCCs and can receive FlowSpecs in messages from PCCs.

   The presence of the PCE FlowSpec Capability TLV in the OPEN Object in
   a PCC's OPEN message indicates that the PCC supports the FlowSpec
   functionality described in this document.

   If either one of a pair of PCEP peers does not include the PCE
   FlowSpec Capability TLV in the OPEN Object in its OPEN message, then
   the other peer MUST NOT include a FLOWSPEC object in any PCEP message
   sent to the peer.  If a FLOWSPEC object is received when support has
   not been indicated, the receiver will respond with a PCErr message
   reporting the objects containing the FlowSpec as described in



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   [RFC5440]: that is, it will use 'Unknown Object' if it does not
   support this specification, and 'Not supported object' if it supports
   this specification but has not chosen to support FLOWSPEC objects on
   this PCEP session.

3.2.1.2.  IGP PCE Capabilities Advertisement

   The ability to advertise support for PCEP and PCE features in IGP
   advertisements is provided for OSPF in [RFC5088] and for IS-IS in
   [RFC5089].  The mechanism uses the PCE Discovery TLV which has a PCE-
   CAP-FLAGS sub-TLV containing bit-flags each of which indicates
   support for a different feature.

   This document defines a new PCE-CAP-FLAGS sub-TLV bit, the FlowSpec
   Capable flag (bit number TBD1).  Setting the bit indicates that an
   advertising PCE supports the procedures defined in this document.

   Note that while PCE FlowSpec Capability may be advertised during
   discovery, PCEP speakers that wish to use Flow Specification in PCEP
   MUST negotiate PCE FlowSpec Capability during PCEP session setup, as
   specified in Section 3.2.1.1.  A PCC MAY initiate PCE FlowSpec
   Capability negotiation at PCEP session setup even if it did not
   receive any IGP PCE capability advertisement, and a PCEP peer that
   advertised support for FlowSpec in the IGP is not obliged to support
   these procedures on any given PCEP session.

3.2.2.  Dissemination Procedures

   This section describes the procedures to support Flow Specifications
   in PCEP messages.

   The primary purpose of distributing Flow Specification information is
   to allow a PCE to indicate to a PCC what traffic it should place on a
   path (such as an LSP or an SR path).  This means that the Flow
   Specification may be included in:

   o  PCInitiate messages so that an active PCE can indicate the traffic
      to place on a path at the time that the PCE instantiates the path.

   o  PCUpd messages so that an active PCE can indicate or change the
      traffic to place on a path that has already been set up.

   o  PCRpt messages so that a PCC can report the traffic that the PCC
      will place on the path.

   o  PCReq messages so that a PCC can indicate what traffic it plans to
      place on a path at the time it requests the PCE to perform a
      computation in case that information aids the PCE in its work.



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   o  PCRep messages so that a PCE that has been asked to compute a path
      can suggest which traffic could be placed on a path that a PCC may
      be about to set up.

   o  PCErr messages so that issues related to paths and the traffic
      they carry can be reported to the PCE by the PCC, and so that
      problems with other PCEP messages that carry Flow Specifications
      can be reported.

   To carry Flow Specifications in PCEP messages, this document defines
   a new PCEP object called the PCEP FLOWSPEC object.  The object is
   OPTIONAL in the messages described above and MAY appear more than
   once in each message.

   To describe a traffic flow, the PCEP FLOWSPEC object carries one of
   the following combinations of TLVs:

   o  zero or one Flow Filter TLV

   o  one L2 Flow Filter TLV

   o  both a Flow Filter TLV and an L2 Flow Filter TLV

   The inclusion of multiple PCEP FLOWSPEC objects allows multiple
   traffic flows to be placed on a single path.

   Once a PCE and PCC have established that they can both support the
   use of Flow Specifications in PCEP messages, such information may be
   exchanged at any time for new or existing paths.

   The application and prioritization of Flow Specifications is
   described in Section 8.7.

   As per [RFC8231], any attributes of the path received from a PCE are
   subject to PCC's local policy.  This holds good for the Flow
   Specifications as well.

3.2.3.  Flow Specification Synchronization

   The Flow Specifications are carried along with the LSP State
   information as per [RFC8231] making the Flow Specifications part of
   the LSP database (LSP-DB).  Thus, the synchronization of the Flow
   Specification information is done as part of LSP-DB synchronization.
   This may be achieved using normal state synchronization procedures as
   described in [RFC8231] or enhanced state synchronization procedures
   as defined in [RFC8232].





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   The approach selected will be implementation and deployment specific
   and will depend on issues such as how the databases are constructed
   and what level of synchronization support is needed.

4.  PCE FlowSpec Capability TLV

   The PCE-FLOWSPEC-CAPABILITY TLV is an optional TLV that can be
   carried in the OPEN Object [RFC5440] to exchange PCE FlowSpec
   capabilities of the PCEP speakers.

   The format of the PCE-FLOWSPEC-CAPABILITY TLV follows the format of
   all PCEP TLVs as defined in [RFC5440] and is shown in Figure 1.


    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=TBD2             |          Length=2             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Value=0             |          Padding              |
   +---------------------------------------------------------------+


               Figure 1: PCE-FLOWSPEC-CAPABILITY TLV format

   The type of the PCE-FLOWSPEC-CAPABILITY TLV is TBD2 and it has a
   fixed length of 2 octets.  The Value field MUST be set to 0 and MUST
   be ignored on receipt.  The two bytes of padding MUST be set to zero
   and ignored on receipt.

   The inclusion of this TLV in an OPEN object indicates that the sender
   can perform FlowSpec handling as defined in this document.

5.  PCEP FLOWSPEC Object

   The PCEP FLOWSPEC object defined in this document is compliant with
   the PCEP object format defined in [RFC5440].  It is OPTIONAL in the
   PCReq, PCRep, PCErr, PCInitiate, PCRpt, and PCUpd messages and MAY be
   present zero, one, or more times.  Each instance of the object
   specifies a separate traffic flow.

   The PCEP FLOWSPEC object carries a FlowSpec filter rule encoded in a
   TLV (a Flow Filter TLV, a single L2 Flow Filter TLV, or both) as
   defined in Section 6).

   The FLOWSPEC Object-Class is TBD3 (to be assigned by IANA).

   The FLOWSPEC Object-Type is 1.



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   The format of the body of the PCEP FLOWSPEC object is shown in
   Figure 2


    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            FS-ID                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         AFI                   |  Reserved     |   Flags   |L|R|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                             TLVs                            //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                Figure 2: PCEP FLOWSPEC Object Body Format

   FS-ID (32-bits): A PCEP-specific identifier for the FlowSpec
   information.  A PCE or PCC creates an FS-ID for each FlowSpec that it
   originates, and the value is unique within the scope of that PCE or
   PCC and is constant for the lifetime of a PCEP session.  All
   subsequent PCEP messages can identify the FlowSpec using the FS-ID.
   The values 0 and 0xFFFFFFFF are reserved and MUST NOT be used.  Note
   that [I-D.gont-numeric-ids-sec-considerations] gives advice on
   assigning transient numeric identifiers such as the FS-ID so as to
   minimise security risks.

   AFI (16-bits): Address Family Identifier as used in BGP [RFC4760]
   (AFI=1 for IPv4 or VPNv4, AFI=2 for IPv6 and VPNv6 as per as per
   [I-D.ietf-idr-flow-spec-v6]).

   Reserved (8-bits): MUST be set to zero on transmission and ignored on
   receipt.

   Flags (8-bits): Two flags are currently assigned -

      R bit: The Remove bit is set when a PCEP FLOWSPEC object is
      included in a PCEP message to indicate removal of the Flow
      Specification from the associated tunnel.  If the bit is clear,
      the Flow Specification is being added or modified.

      L bit: The Longest Prefix Match (LPM) bit is set to indicate that
      the Flow Specification is to be installed as a route subject to
      longest prefix match forwarding.  If the bit is clear, the Flow
      Specification described by the Flow Filter TLV (see Section 6) is
      to be installed as a Flow Specification.  If the bit is set, only



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      Flow Specifications that describe IPv4 or IPv6 destinations are
      meaningful in the Flow Filter TLV and others are ignored.  If the
      L is set and the receiver does not support the use of Flow
      Specifications that are present in the Flow Filter TLV for the
      installation of a route subject to longest prefix match
      forwarding, then the PCEP peer MUST respond with a PCErr message
      with error-type TBD8 (FlowSpec Error) and error-value 5
      (Unsupported LPM Route).

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

   If the PCEP speaker receives a message with R bit set in the FLOWSPEC
   object and the Flow Specification identified with a FS-ID does not
   exist, it MUST generate a PCErr with Error-type TBD8 (FlowSpec
   Error), error-value 4 (Unknown FlowSpec).

   If the PCEP speaker does not understand or support the AFI in the
   FLOWSPEC message, the PCEP peer MUST respond with a PCErr message
   with error-type TBD8 (FlowSpec Error), error-value 2 (Malformed
   FlowSpec).

   The following TLVs can be used in the FLOWSPEC object:

   o  Speaker Entity Identifier TLV: As specified in [RFC8232], the
      SPEAKER-ENTITY-ID TLV encodes a unique identifier for the node
      that does not change during the lifetime of the PCEP speaker.
      This is used to uniquely identify the FlowSpec originator and thus
      used in conjunction with FS-ID to uniquely identify the FlowSpec
      information.  This TLV MUST be included.  If the TLV is missing,
      the PCEP peer MUST respond with a PCErr message with error-type
      TBD8 (FlowSpec Error), error-value 2 (Malformed FlowSpec).  If
      more than one instance of this TLV is present, the first MUST be
      processed and subsequence instances MUST be ignored.

   o  Flow Filter TLV (variable): One TLV MAY be included.  The Flow
      Filter TLV is OPTIONAL when the R bit is set.

   o  L2 Flow Filter TLV (variable): One TLV MAY be included.  The L2
      Flow Filter TLV is OPTIONAL when the R bit is set.

   At least one Flow Filter TLV or one L2 Flow Filter TLV MUST be
   present when the R bit is clear.  If both TLVs are missing when the R
   bit is clear, the PCEP peer MUST respond with a PCErr message with
   error-type TBD8 (FlowSpec Error) and error-value 2 (Malformed
   FlowSpec).  A Flow Filter TLV and a L2 Flow Filter TLV MAY both be
   present when filtering is based on both L3 and L2 fields.




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6.  Flow Filter TLV and L2 Flow Filter TLV

   Two new PCEP TLVs are defined to convey Flow Specification filtering
   rules that specify what traffic is carried on a path.  The TLVs
   follow the format of all PCEP TLVs as defined in [RFC5440].  The Type
   field values come from the codepoint space for PCEP TLVs and has the
   value TBD4 for Flow Filter TLV and TBD9 for L2 Flow Filter TLV.

   The Value fields of the TLVs contain one or more sub-TLVs (the Flow
   Specification TLVs or L2 Flow Specification TLVs) as defined in
   Section 7, and they represent the complete definition of a Flow
   Specification for traffic to be placed on the tunnel.  This tunnel is
   indicated by the PCEP message in which the PCEP FLOWSPEC object is
   carried.  The set of Flow Specification TLVs and L2 Flow Filter TLVs
   in a single instance of a Flow Filter TLV are combined to indicate
   the specific Flow Specification.  Note that the PCEP FLOWSPEC object
   can include just one Flow Filter TLV, just one L2 Flow Filter TLV, or
   one of each TLV.

   Further Flow Specifications can be included in a PCEP message by
   including additional FLOWSPEC objects.

7.  Flow Specification TLVs

   The Flow Filter TLV carries one or more Flow Specification TLVs.  The
   Flow Specification TLV follows the format of all PCEP TLVs as defined
   in [RFC5440].  However, the Type values are selected from a separate
   IANA registry (see Section 10.3) rather than from the common PCEP TLV
   registry.

   Type values are chosen so that there can be commonality with Flow
   Specifications defined for use with BGP [I-D.ietf-idr-rfc5575bis] and
   [I-D.ietf-idr-flow-spec-v6].  This is possible because the BGP Flow
   Spec encoding uses a single octet to encode the type where as PCEP
   uses two octets.  Thus the space of values for the Type field is
   partitioned as shown in Figure 3.















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   Range          |
   ---------------+---------------------------------------------------
   0 .. 255       | Per BGP registry defined by
                  | [I-D.ietf-idr-rfc5575bis] and
                  | [I-D.ietf-idr-flow-spec-v6].
                  | Not to be allocated in this registry.
                  |
   256 ..   65535 | New PCEP Flow Specifications allocated according
                  | to the registry defined in this document.


               Figure 3: Flow Specification TLV Type Ranges

   [I-D.ietf-idr-rfc5575bis] is the reference for the registry "Flow
   Spec Component Types" and defines the allocations it contains.
   [I-D.ietf-idr-flow-spec-v6] requested for another registry "Flow Spec
   IPv6 Component Types" and requested initial allocations in it.  If
   the AFI (in the FLOWSPEC object) is set to IPv4, the range 0..255 is
   as per "Flow Spec Component Types" [I-D.ietf-idr-rfc5575bis]; if the
   AFI is set to IPv6, the range 0..255 is as per "Flow Spec IPv6
   Component Types" [I-D.ietf-idr-flow-spec-v6].

   The content of the Value field in each TLV is specific to the type/
   AFI and describes the parameters of the Flow Specification.  The
   definition of the format of many of these Value fields is inherited
   from BGP specifications.  Specifically, the inheritance is from
   [I-D.ietf-idr-rfc5575bis] and [I-D.ietf-idr-flow-spec-v6], but may
   also be inherited from future BGP specifications.

   When multiple Flow Specification TLVs are present in a single Flow
   Filter TLV they are combined to produce a more detailed specification
   of a flow.  For examples and rules about how this is achieved, see
   [I-D.ietf-idr-rfc5575bis].  As described in [I-D.ietf-idr-rfc5575bis]
   where it says "A given component type MAY (exactly once) be present
   in the Flow Specification," a Flow Filter TLV MUST NOT contain more
   than one Flow Specification TLV of the same type: an implementation
   that receives a PCEP message with a Flow Flter TLV that contains more
   than one Flow Specification TLV of the same type MUST respond with a
   PCErr message with error-type TBD8 (FlowSpec Error), error-value 2
   (Malformed FlowSpec) and MUST NOT install the Flow Specification.

   An implementation that receives a PCEP message carrying a Flow
   Specification TLV with a type value that it does not recognize or
   does not support MUST respond with a PCErr message with error-type
   TBD8 (FlowSpec Error), error-value 1 (Unsupported FlowSpec) and MUST
   NOT install the Flow Specification.





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   When used in other protocols (such as BGP), these Flow Specifications
   are also associated with actions to indicate how traffic matching the
   Flow Specification should be treated.  In PCEP, however, the only
   action is to associate the traffic with a tunnel and to forward
   matching traffic onto that path, so no encoding of an action is
   needed.

   Section 8.7 describes how overlapping Flow Specifications are
   prioritized and handled.

   All Flow Specification TLVs with Types in the range 0 to 255 have
   Values defined for use in BGP (for example, in
   [I-D.ietf-idr-rfc5575bis] and [I-D.ietf-idr-flow-spec-v6]) and are
   set using the BGP encoding, but without the type octet (the relevant
   information is in the Type field of the TLV).  The Value field is
   padded with trailing zeros to achieve 4-byte alignment.

   This document defines the following new types:


   +-------+-------------------------+-----------------------------+
   | Type  | Description             | Value defined in            |
   |       |                         |                             |
   +-------+-------------------------+-----------------------------+
   | TBD5  | Route Distinguisher     | [This.I-D]                  |
   +-------+-------------------------+-----------------------------+
   | TBD6  | IPv4 Multicast Flow     | [This.I-D]                  |
   +-------+-------------------------+-----------------------------+
   | TBD7  | IPv6 Multicast Flow     | [This.I-D]                  |
   +-------+-------------------------+-----------------------------+



      Figure 4: Table of Flow Specification TLV Types defined in this
                                 document

   To allow identification of a VPN in PCEP via a Route Distinguisher
   (RD) [RFC4364], a new TLV - ROUTE-DISTINGUISHER TLV is defined in
   this document.  A Flow Specification TLV with Type TBD5 (ROUTE-
   DISTINGUISHER TLV) carries an RD Value, used to identify that other
   flow filter information (for example, an IPv4 destination prefix) is
   associated with a specific VPN identified by the RD.  See Section 8.6
   for further discussion of VPN identification.








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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Type=[TBD5]         |           Length=8            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Route Distinguisher                       |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


            Figure 5: The Format of the ROUTE-DISTINGUISHER TLV

   The format of RD is as per [RFC4364].

   Although it may be possible to describe a multicast Flow
   Specification from the combination of other Flow Specification TLVs
   with specific values, it is more convenient to use a dedicated Flow
   Specification TLV.  Flow Specification TLVs with Type values TBD6 and
   TBD7 are used to identify a multicast flow for IPv4 and IPv6
   respectively.  The Value field is encoded as 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Reserved           |S|G|  Src Mask Len | Grp Mask Len  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                        Source Address                         ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                   Group multicast Address                     ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


            Figure 6: Multicast Flow Specification TLV Encoding

   The address fields and address mask lengths of the two Multicast Flow
   Specification TLVs contain source and group prefixes for matching
   against packet flows noting that the two address fields are 32 bits
   for an IPv4 Multicast Flow and 128 bits for an IPv6 Multicast Flow.

   The Reserved field MUST be set to zero and ignored on receipt.

   Two bit flags (S and G) are defined to describe the multicast
   wildcarding in use.  If the S bit is set, then source wildcarding is
   in use and the values in the Source Mask Length and Source Address
   fields MUST be ignored.  If the G bit is set, then group wildcarding
   is in use and the values in the Group Mask Length and Group multicast
   Address fields MUST be ignored.  The G bit MUST NOT be set unless the



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   S bit is also set: if a Multicast Flow Specification TLV is received
   with S bit = 0 and G bit = 1 the receiver MUST respond with a PCErr
   with Error-type TBD8 (FlowSpec Error) and error-value 2 (Malformed
   FlowSpec).

   The three multicast mappings may be achieved as follows:

      (S, G) - S bit = 0, G bit = 0, the Source Address and Group
      multicast Address prefixes are both used to define the multicast
      flow.

      (*, G) - S bit = 1, G bit = 0, the Group multicast Address prefix
      is used to define the multicast flow, but the Source Address
      prefix is ignored.

      (*, *) = S bit = 1, G bit = 1, the Source Address and Group
      multicast Address prefixes are both ignored.

7.1.  L2 Flow Specification TLVs

   The L2 Flow Filter TLV carries one or more L2 Flow Specification TLV.
   The L2 Flow Specification TLV follows the format of all PCEP TLVs as
   defined in [RFC5440].  However, the Type values are selected from a
   separate IANA registry (see Section 10.4) rather than from the common
   PCEP TLV registry.

   Type values are chosen so that there can be commonality with L2 Flow
   Specifications defined for use with BGP
   [I-D.ietf-idr-flowspec-l2vpn].  This is possible because the BGP Flow
   Spec encoding uses a single octet to encode the type where as PCEP
   uses two octets.  Thus the space of values for the Type field is
   partitioned as shown in Figure 7.


      Range          |
      ---------------+-------------------------------------------------
      0 .. 255       | Per BGP registry defined by
                     | [I-D.ietf-idr-flowspec-l2vpn].
                     | Not to be allocated in this registry.
                     |
      256 ..   65535 | New PCEP Flow Specifications allocated according
                     | to the registry defined in this document.


              Figure 7: L2 Flow Specification TLV Type Ranges

   [I-D.ietf-idr-flowspec-l2vpn] is the reference for the registry "L2
   Flow Spec Component Types" and defines the allocations it contains.



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   The content of the Value field in each TLV is specific to the type
   and describes the parameters of the Flow Specification.  The
   definition of the format of many of these Value fields is inherited
   from BGP specifications.  Specifically, the inheritance is from
   [I-D.ietf-idr-flowspec-l2vpn], but may also be inherited from future
   BGP specifications.

   When multiple L2 Flow Specification TLVs are present in a single L2
   Flow Filter TLV they are combined to produce a more detailed
   specification of a flow.  Similarly, when both Flow Filter TLV and L2
   Flow Filter TLV are present, they are combined to produce a more
   detailed specification of a flow.

   An implementation that receives a PCEP message carrying a L2 Flow
   Specification TLV with a type value that it does not recognize or
   does not support MUST respond with a PCErr message with error-type
   TBD8 (FlowSpec Error), error-value 1 (Unsupported FlowSpec) and MUST
   NOT install the Flow Specification.

   All L2 Flow Specification TLVs with Types in the range 0 to 255 have
   their Values interpretted as defined for use in BGP (for example, in
   [I-D.ietf-idr-flowspec-l2vpn]) and are set using the BGP encoding,
   but without the type octet (the relevant information is in the Type
   field of the TLV).  The Value field is padded with trailing zeros to
   achieve 4-byte alignment.

   This document defines no new types.

   In the rest of the document when the Flow Specification is mentioned,
   it includes the L2 Flow Specifications as well.

8.  Detailed Procedures

   This section outlines some specific detailed procedures for using the
   protocol extensions defined in this document.

8.1.  Default Behavior and Backward Compatibility

   The default behavior is that no Flow Specification is applied to a
   tunnel.  That is, the default is that the FLOWSPEC object is not used
   as is the case in all systems before the implementation of this
   specification.

   In this case, it is a local matter (such as through configuration)
   how tunnel head ends are instructed what traffic to place on a
   tunnel.





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   [RFC5440] describes how receivers respond when they see unknown PCEP
   objects.

8.2.  Composite Flow Specifications

   Flow Specifications may be represented by a single Flow Specification
   TLV or may require a more complex description using multiple Flow
   Specification TLVs.  For example, a flow indicated by a source-
   destination pair of IPv6 addresses would be described by the
   combination of Destination IPv6 Prefix and Source IPv6 Prefix Flow
   Specification TLVs.

8.3.  Modifying Flow Specifications

   A PCE may want to modify a Flow Specification associated with a
   tunnel, or a PCC may want to report a change to the Flow
   Specification it is using with a tunnel.

   It is important that the specific Flow Specification is identified so
   that it is clear that this is a modification of an existing flow and
   not the addition of a new flow as described in Section 8.4.  The FS-
   ID field of the PCEP FLOWSPEC object is used to identify a specific
   Flow Specification in the context of the content of the Speaker
   Entity Identifier TLV.

   When modifying a Flow Specification, all Flow Specification TLVs for
   the intended specification of the flow MUST be included in the PCEP
   FLOWSPEC object. the FS-ID MUST be retained from the previous
   description of the flow, and the same Speaker Entity Identity TLV
   MUST be used.

8.4.  Multiple Flow Specifications

   It is possible that traffic from multiple flows will be placed on a
   single tunnel.  In some cases it is possible to define these within a
   single PCEP FLOWSPEC object by widening the scope of a Flow
   Specification TLV: for example, traffic to two destination IPv4
   prefixes might be captured by a single Flow Specification TLV with
   type 'Destination' with a suitably adjusted prefix.  However, this is
   unlikely to be possible in most scenarios, and it must be recalled
   that it is not permitted to include two Flow Specification TLVs of
   the same type within one Flow Filter TLV.

   The normal procedure, therefore, is to carry each Flow Specification
   in its own PCEP FLOWSPEC object.  Multiple objects may be present on
   a single PCEP message, or multiple PCEP messages may be used.





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8.5.  Adding and Removing Flow Specifications

   The Remove bit in the PCEP FLOWSPEC object is left clear when a Flow
   Specification is being added or modified.

   To remove a Flow Specification, a PCEP FLOWSPEC object is included
   with the FS-ID matching the one being removed, and the R bit set to
   indicate removal.  In this case it is not necessary to include any
   Flow Specification TLVs.

   If the R bit is set and Flow Specification TLVs are present, an
   implementation MAY ignore them.  If the implementation checks the
   Flow Specification TLVs against those recorded for the FS-ID and
   Speaker Entity Identity of the Flow Specification being removed and
   finds a mismatch, the Flow Specification matching the FS-ID MUST
   still be removed and the implementation SHOULD record a local
   exception or log.

8.6.  VPN Identifiers

   VPN instances are identified in BGP using Route Distinguishers (RDs)
   [RFC4364].  These values are not normally considered to have any
   meaning outside of the network, and they are not encoded in data
   packets belonging to the VPNs.  However, RDs provide a useful way of
   identifying VPN instances and are often manually or automatically
   assigned to VPNs as they are provisioned.

   Thus the RD provides a useful way to indicate that traffic for a
   particular VPN should be placed on a given tunnel.  The tunnel head
   end will need to interpret this Flow Specification not as a filter on
   the fields of data packets, but using the other mechanisms that it
   already uses to identify VPN traffic.  This could be based on the
   incoming port (for port-based VPNs) or may leverage knowledge of the
   VRF that is in use for the traffic.

8.7.  Priorities and Overlapping Flow Specifications

   Flow specifications can overlap.  For example, two different flow
   specifications may be identical except for the length of the prefix
   in the destination address.  In these cases the PCC must determine
   how to prioritize the flow specifications so as to know to which path
   to assign packets that match both flow specifications.  That is, the
   PCC must assign a precedence to the flow specifications so that it
   checks each incoming packet for a match in a predictable order.

   The processing of BGP Flow Specifications is described in
   [I-D.ietf-idr-rfc5575bis].  Section 5.1 of that document explains the




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   order of traffic filtering rules to be executed by an implementation
   of that specification.

   PCCs MUST apply the same ordering rules as defined in
   [I-D.ietf-idr-rfc5575bis].

   Furthermore, it is possible that Flow Specifications will be
   distributed by BGP as well as by PCEP as described in this document.
   In such cases implementations supporting both approaches MUST apply
   the prioritization and ordering rules as set out in
   [I-D.ietf-idr-rfc5575bis] regardless of which protocol distributed
   the Flow Specifications.  However, implementations MAY provide a
   configuration control to allow one protocol to take precedence over
   the other as this may be particularly useful if the Flow
   Specifications make identical matches on traffic, but have different
   actions.  It is RECOMMENDED that when two Flow Specifications
   distributed by different protocols overlap, and especially when one
   acts to replace another, that a message be logged for the operator to
   understand the behaviour.

   Section 13.1 of this document covers manageability considerations
   relevant to the prioritized ordering of flow specifications.

   An implementation that receives a PCEP message carrying a Flow
   Specification that it cannot resolve against other Flow
   Specifications already installed (for example, because the new Flow
   Specification has irresolvable conflicts with other Flow
   Specifications that are already installed) MUST respond with a PCErr
   message with error-type TBD8 (FlowSpec Error), error-value 3
   (Unresolvable Conflict) and MUST NOT install the Flow Specification.

9.  PCEP Messages

   This section describes the format of messages that contain FLOWSPEC
   objects.  The only difference to previous message formats is the
   inclusion of that object.

   The figures in this section use the notation defined in [RFC5511].

   The FLOWSPEC object is OPTIONAL and MAY be carried in the PCEP
   messages.

   The PCInitiate message is defined in [RFC8281] and updated as below:








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   <PCInitiate Message> ::= <Common Header>
                            <PCE-initiated-lsp-list>

   Where:
      <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-instantiation> ::= <SRP>
                                            <LSP>
                                            [<END-POINTS>]
                                            <ERO>
                                            [<attribute-list>]
                                            [<flowspec-list>]

      Where:
         <flowspec-list> ::= <FLOWSPEC> [<flowspec-list>]


   The PCUpd message is defined in [RFC8231] and updated as below:


   <PCUpd Message> ::= <Common Header>
                       <update-request-list>

   Where:
      <update-request-list> ::= <update-request>
                                [<update-request-list>]

      <update-request> ::= <SRP>
                           <LSP>
                           <path>
                           [<flowspec-list>]

      Where:
         <path>::= <intended-path><intended-attribute-list>

         <flowspec-list> ::= <FLOWSPEC> [<flowspec-list>]


   The PCRpt message is defined in [RFC8231] and updated as below:







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

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

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

       Where:
         <path>::= <intended-path>
                   [<actual-attribute-list><actual-path>]
                   <intended-attribute-list>

         <flowspec-list> ::= <FLOWSPEC> [<flowspec-list>]


   The PCReq message is defined in [RFC5440] and updated in [RFC8231],
   it is further updated below for flow specification:


   <PCReq Message>::= <Common Header>
                      [<svec-list>]
                      <request-list>

   Where:
      <svec-list>::= <SVEC>[<svec-list>]

      <request-list>::= <request>[<request-list>]

      <request>::= <RP>
                   <END-POINTS>
                   [<LSP>]
                   [<LSPA>]
                   [<BANDWIDTH>]
                   [<metric-list>]
                   [<RRO>[<BANDWIDTH>]]
                   [<IRO>]
                   [<LOAD-BALANCING>]
                   [<flowspec-list>]

      Where:
         <flowspec-list> ::= <FLOWSPEC> [<flowspec-list>]






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   The PCRep message is defined in [RFC5440] and updated in [RFC8231],
   it is further updated below for flow specification:


   <PCRep Message> ::= <Common Header>
                       <response-list>

   Where:
      <response-list>::=<response>[<response-list>]

      <response>::=<RP>
                  [<LSP>]
                  [<NO-PATH>]
                  [<attribute-list>]
                  [<path-list>]
                  [<flowspec-list>]

      Where:
         <flowspec-list> ::= <FLOWSPEC> [<flowspec-list>]


10.  IANA Considerations

   IANA maintains the "Path Computation Element Protocol (PCEP) Numbers"
   registry.  This document requests IANA actions to allocate code
   points for the protocol elements defined in this document.

10.1.  PCEP Objects

   Each PCEP object has an Object-Class and an Object-Type.  IANA
   maintains a subregistry called "PCEP Objects".  IANA is requested to
   make an assignment from this subregistry as follows:


   Object-Class | Value Name  | Object-Type            |  Reference
   -------------+-------------+------------------------+----------------
      TBD3      | FLOWSPEC    |  0: Reserved           |  [This.I-D]
                |             |  1: Flow Specification |  [This.I-D]


10.1.1.  PCEP FLOWSPEC Object Flag Field

   This document requests that a new sub-registry, named "FLOWSPEC
   Object Flag Field", is created within the "Path Computation Element
   Protocol (PCEP) Numbers" registry to manage the Flag field of the
   FLOWSPEC object.  New values are to be assigned by Standards Action
   [RFC8126].  Each bit should be tracked with the following qualities:




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

   o  Capability description

   o  Defining RFC

   The initial population of this registry is as follows:


    Bit  |  Description       |  Reference
    -----+--------------------+-------------
    0-5  |  Unnassigned       |
      6  |  LPM (L bit)       |  [This.I-D]
      7  |  Remove (R bit)    |  [This.I-D]


10.2.  PCEP TLV Type Indicators

   IANA maintains a subregistry called "PCEP TLV Type Indicators".  IANA
   is requested to make an assignment from this subregistry as follows:


   Value   | Meaning                      | Reference
   --------+------------------------------+-------------
    TBD2   | PCE-FLOWSPEC-CAPABILITY TLV  | [This.I-D]
    TBD4   | FLOW FILTER TLV              | [This.I-D]
    TBD9   | L2 FLOW FILTER TLV           | [This.I-D]


10.3.  Flow Specification TLV Type Indicators

   IANA is requested to create a new subregistry call the "PCEP Flow
   Specification TLV Type Indicators" registry.

   Allocations from this registry are to be made according to the
   following assignment policies [RFC8126]:















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   Range          | Assignment policy
   ---------------+---------------------------------------------------
   0 .. 255       | Reserved - must not be allocated.
                  | Usage mirrors the BGP FlowSpec registry
                  | [I-D.ietf-idr-rfc5575bis] and
                  | [I-D.ietf-idr-flow-spec-v6].
                  |
   256 ..   64506 | Specification Required
                  |
   64507 .. 65531 | First Come First Served
                  |
   65532 .. 65535 | Experimental


   IANA is requested to pre-populate this registry with values defined
   in this document as follows, taking the new values from the range 256
   to 64506:


    Value | Meaning
   -------+------------------------
    TBD5  | Route Distinguisher
    TBD6  | IPv4 Multicast
    TBD7  | IPv6 Multicast


10.4.  L2 Flow Specification TLV Type Indicators

   IANA is requested to create a new subregistry called the "PCEP L2
   Flow Specification TLV Type Indicators" registry.

   Allocations from this registry are to be made according to the
   following assignment policies [RFC8126]:


    Range          | Assignment policy
    ---------------+---------------------------------------------------
    0 .. 255       | Reserved - must not be allocated.
                   | Usage mirrors the BGP L2 FlowSpec registry
                   | [I-D.ietf-idr-flowspec-l2vpn].
                   |
    256 ..   64506 | Specification Required
                   |
    64507 .. 65531 | First Come First Served
                   |
    65532 .. 65535 | Experimental





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10.5.  PCEP Error Codes

   IANA maintains a subregistry called "PCEP-ERROR Object Error Types
   and Values".  Entries in this subregistry are described by Error-Type
   and Error-value.  IANA is requested to make the following assignment
   from this subregistry:


    Error-| Meaning            | Error-value                | Reference
    Type  |                    |                            |
   -------+--------------------+----------------------------+-----------
    TBD8  | FlowSpec error     | 0: Unassigned              | [This.I-D]
          |                    | 1: Unsupported FlowSpec    | [This.I-D]
          |                    | 2: Malformed FlowSpec      | [This.I-D]
          |                    | 3: Unresolvable Conflict   | [This.I-D]
          |                    | 4: Unknown FlowSpec        | [This.I-D]
          |                    | 5: Unsupported LPM Route   | [This.I-D]
          |                    | 6-255: Unassigned          | [This.I-D]


10.6.  PCE Capability Flag

   IANA maintains a subregistry called "Open Shortest Path First v2
   (OSPFv2) Parameters" with a sub-registry called "Path Computation
   Element (PCE) Capability Flags".  IANA is requested to assign a new
   capability bit from this registry as follows:


    Bit   | Capability Description        | Reference
   -------+-------------------------------+------------
    TBD1  | FlowSpec                      | [This.I-D]


11.  Implementation Status

   [NOTE TO RFC EDITOR : This whole section and the reference to RFC
   7942 is to be removed before publication as an RFC]

   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



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   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".

   At the time of posting the -12 version of this document, there are no
   known implementations of this mechanism.  It is believed that two
   vendors are considering prototype implementations, but these plans
   are too vague to make any further assertions.

12.  Security Considerations

   We may assume that a system that utilizes a remote PCE is subject to
   a number of vulnerabilities that could allow spurious LSPs or SR
   paths to be established or that could result in existing paths being
   modified or torn down.  Such systems, therefore, apply security
   considerations as described in [RFC5440], Section 2.5 of [RFC6952],
   [RFC8253], and [I-D.ietf-idr-rfc5575bis].

   The description of Flow Specifications associated with paths set up
   or controlled by a PCE add a further detail that could be attacked
   without tearing down LSPs or SR paths, but causing traffic to be
   misrouted within the network.  Therefore, the use of the security
   mechanisms for PCEP referenced above is important.

   Visibility into the information carried in PCEP does not have direct
   privacy concerns for end-users' data, however, knowledge of how data
   is routed in a network may make that data more vulnerable.  Of
   course, the ability to interfere with the way data is routed also
   makes the data more vulnerable.  Furthermore, knowledge of the
   connected end-points (such as multicast receivers or VPN sites) is
   usually considered private customer information.  Therefore,
   implementations or deployments concerned with protecting privacy MUST
   apply the mechanisms described in the documents referenced above: in
   particular to secure the PCEP session using IPSec per Sections 10.4
   to 10.6 of [RFC5440] or TLS per [RFC8253].  Note that TCP-MD5
   security as originally suggested in [RFC5440] does not provide
   sufficient security or privacy guarantees, and SHOULD NOT be relied
   upon.

   Experience with Flow Specifications in BGP systems indicates that
   they can become complex and that the overlap of Flow Specifications
   installed in different orders can lead to unexpected results.



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   Although this is not directly a security issue per se, the confusion
   and unexpected forwarding behavior may be engineered or exploited by
   an attacker.  Furthermore, this complexity might give rise to a
   situation where the forwarding behaviors might create gaps in the
   monitoring and inspection of particular traffic or provide a path
   that avoids expected mitigations.  Therefore, implementers and
   operators SHOULD pay careful attention to the Manageability
   Considerations described in Section 13 and familiarize themselves
   with the careful explanations in [I-D.ietf-idr-rfc5575bis].

13.  Manageability Considerations

   The feature introduced by this document enables operational
   manageability of networks operated in conjunction with a PCE and
   using PCEP.  Without this feature, but in the case of a stateful
   active PCE or with PCE-initiated services, additional manual
   configuration is needed to tell the head-ends what traffic to place
   on the network services (LSPs, SR paths, etc.).

   This section follows the advice and guidance of [RFC6123].

13.1.  Management of Multiple Flow Specifications

   Experience with flow specification in BGP suggests that there can be
   a lot of complexity when two or more flow specifications overlap.
   This can arise, for example, with addresses indicated using prefixes,
   and could cause confusion about what traffic should be placed on
   which path.  Unlike the behavior in a distributed routing system, it
   is not important to the routing stablity and consistency of the
   network that each head-end implementation applies the same rules to
   disambiguate overlapping Flow Specifications, but it is important
   that:

   o  A network operator can easily find out what traffic is being
      placed on which path and why.  This will facilitate analysis of
      the network and diagnosis of faults.

   o  A PCE is able to correctly predict the effect of instructions it
      gives to a PCC.  This will ensure that traffic is correctly placed
      on the network without causing congestion or other network
      inefficiencies, and that traffic is correctly delivered.

   To that end, a PCC MUST enable an operator to view the the Flow
   Specifications that it has installed, and these MUST be presented in
   order of precedence such that when two Flow Specifications overlap,
   the one that will be serviced with higher precedence is presented to
   the operator first.




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   A discussion of precedence ordering for flow specifications is found
   in Section 8.7.

13.2.  Control of Function through Configuration and Policy

   Support for the function described in this document implies that a
   functional element that is capable of requesting a PCE to compute and
   control a path is also able to configure the specification of what
   traffic should be placed on that path.  Where there is a human
   involved in this action, configuration of the Flow Specification must
   be available through an interface (such as a graphical user interface
   or a command line interface).  Where a distinct software component
   (i.e., one not co-implemented with the PCE) is used, a protocol
   mechanism will be required that could be PCEP itself or could be a
   data model such as extensions to the YANG model for requesting path
   computation [I-D.ietf-teas-yang-path-computation].

   Implementations MAY be constructed with a configurable switch to say
   whether they support the functions defined in this document.
   Otherwise, such implementations MUST indicate that they support the
   function as described in Section 4.  If an implementation supports
   configurable support of this function, that support MAY be
   configurable per peer or once for the whole implementation.

   As mentioned in Section 13.1, a PCE implementation SHOULD provide a
   mechanism to configure variations in the precedence ordering of Flow
   Specifications per PCC.

13.3.  Information and Data Models

   The YANG model in [I-D.ietf-pce-pcep-yang] can be used to model and
   monitor PCEP states and messages.  To make that YANG model useful for
   the extensions described in this document, it would need to be
   augmented to cover the new protocol elements.

   Similarly, as noted in Section 13.2, the YANG model defined in
   [I-D.ietf-teas-yang-path-computation] could be extended to allow
   specification of Flow Specifications.

   Finally, as mentioned in Section 13.1, a PCC implementation SHOULD
   provide a mechanism to allow an operator to read the Flow
   Specifications from a PCC and to understand in what order they will
   be executed.  This could be achieved using a new YANG model.








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13.4.  Liveness Detection and Monitoring

   The extensions defined in this document do not require any additional
   liveness detection and monitoring support.  See [RFC5440] and
   [RFC5886] for more information.

13.5.  Verifying Correct Operation

   The chief element of operation that needs to be verified (in addition
   to the operation of the protocol elements as described in [RFC5440])
   is the installation, precedence, and correct operation of the Flow
   Specifications at a PCC.

   In addition to the YANG model for reading Flow Specifications
   described in Section 13.3, tools may be needed to inject Operations
   and Management (OAM) traffic at the PCC that matches specific
   criteria so that it can be monitored as traveling along the desired
   path.  Such tools are outside the scope of this document.

13.6.  Requirements on Other Protocols and Functional Components

   This document places no requirements on other protocols or
   components.

13.7.  Impact on Network Operation

   The use of the features described in this document clearly have an
   important impact on network traffic since they cause traffic to be
   routed on specific paths in the network.  However, in practice, these
   changes make no direct changes to the network operation because
   traffic is already placed on those paths using some pre-existing
   configuration mechanism.  Thus, the significant change is the
   reduction in mechanisms that have to be applied, rather than a change
   to how the traffic is passed through the network.

14.  Acknowledgements

   Thanks to Julian Lucek, Sudhir Cheruathur, Olivier Dugeon, Jayant
   Agarwal, Jeffrey Zhang, Acee Lindem, Vishnu Pavan Beeram, Julien
   Meuric, Deborah Brungard, Eric Vyncke, Erik Kline, Benjamin Kaduk,
   Martin Duke, Roman Danyliw, and Alvaro Retana for useful discussions
   and comments.

15.  References







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15.1.  Normative References

   [I-D.ietf-idr-flow-spec-v6]
              Loibl, C., Raszuk, R., and S. Hares, "Dissemination of
              Flow Specification Rules for IPv6", draft-ietf-idr-flow-
              spec-v6-17 (work in progress), October 2020.

   [I-D.ietf-idr-flowspec-l2vpn]
              Weiguo, H., Eastlake, D., Litkowski, S., and S. Zhuang,
              "BGP Dissemination of L2 Flow Specification Rules", draft-
              ietf-idr-flowspec-l2vpn-15 (work in progress), May 2020.

   [I-D.ietf-idr-rfc5575bis]
              Loibl, C., Hares, S., Raszuk, R., McPherson, D., and M.
              Bacher, "Dissemination of Flow Specification Rules",
              draft-ietf-idr-rfc5575bis-27 (work in progress), October
              2020.

   [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>.

   [RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
              Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
              2006, <https://www.rfc-editor.org/info/rfc4364>.

   [RFC4760]  Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
              "Multiprotocol Extensions for BGP-4", RFC 4760,
              DOI 10.17487/RFC4760, January 2007,
              <https://www.rfc-editor.org/info/rfc4760>.

   [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>.

   [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>.

   [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>.






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

   [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>.

   [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>.

15.2.  Informative References

   [I-D.gont-numeric-ids-sec-considerations]
              Gont, F. and I. Arce, "Security Considerations for
              Transient Numeric Identifiers Employed in Network
              Protocols", draft-gont-numeric-ids-sec-considerations-05
              (work in progress), July 2020.

   [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.ietf-teas-yang-path-computation]
              Busi, I., Belotti, S., Lopez, V., Sharma, A., and Y. Shi,
              "Yang model for requesting Path Computation", draft-ietf-
              teas-yang-path-computation-10 (work in progress), July
              2020.

   [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>.



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   [RFC5088]  Le Roux, JL., Ed., Vasseur, JP., Ed., Ikejiri, Y., and R.
              Zhang, "OSPF Protocol Extensions for Path Computation
              Element (PCE) Discovery", RFC 5088, DOI 10.17487/RFC5088,
              January 2008, <https://www.rfc-editor.org/info/rfc5088>.

   [RFC5089]  Le Roux, JL., Ed., Vasseur, JP., Ed., Ikejiri, Y., and R.
              Zhang, "IS-IS Protocol Extensions for Path Computation
              Element (PCE) Discovery", RFC 5089, DOI 10.17487/RFC5089,
              January 2008, <https://www.rfc-editor.org/info/rfc5089>.

   [RFC5886]  Vasseur, JP., Ed., Le Roux, JL., and Y. Ikejiri, "A Set of
              Monitoring Tools for Path Computation Element (PCE)-Based
              Architecture", RFC 5886, DOI 10.17487/RFC5886, June 2010,
              <https://www.rfc-editor.org/info/rfc5886>.

   [RFC6123]  Farrel, A., "Inclusion of Manageability Sections in Path
              Computation Element (PCE) Working Group Drafts", RFC 6123,
              DOI 10.17487/RFC6123, February 2011,
              <https://www.rfc-editor.org/info/rfc6123>.

   [RFC6952]  Jethanandani, M., Patel, K., and L. Zheng, "Analysis of
              BGP, LDP, PCEP, and MSDP Issues According to the Keying
              and Authentication for Routing Protocols (KARP) Design
              Guide", RFC 6952, DOI 10.17487/RFC6952, May 2013,
              <https://www.rfc-editor.org/info/rfc6952>.

   [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>.

   [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>.

   [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>.

   [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>.





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   [RFC8664]  Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
              and J. Hardwick, "Path Computation Element Communication
              Protocol (PCEP) Extensions for Segment Routing", RFC 8664,
              DOI 10.17487/RFC8664, December 2019,
              <https://www.rfc-editor.org/info/rfc8664>.

Appendix A.  Contributors


   Shankara
   Huawei Technologies
   Divyashree Techno Park,
   Whitefield Bangalore,
   Karnataka
   560066
   India

   Email: shankara@huawei.com

   Qiandeng Liang
   Huawei Technologies
   101 Software Avenue,
   Yuhuatai District
   Nanjing
   210012
   China

   Email: liangqiandeng@huawei.com

   Cyril Margaria
   Juniper Networks
   200 Somerset Corporate Boulevard, Suite 4001
   Bridgewater, NJ
   08807
   USA

   Email: cmargaria@juniper.net

   Colby Barth
   Juniper Networks
   200 Somerset Corporate Boulevard, Suite 4001
   Bridgewater, NJ
   08807
   USA

   Email: cbarth@juniper.net

   Xia Chen



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

   Email: jescia.chenxia@huawei.com

   Shunwan Zhuang
   Huawei Technologies
   Huawei Bld., No.156 Beiqing Rd.
   Beijing
   100095
   China

   Email: zhuangshunwan@huawei.com

   Cheng Li
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Rd.
   Beijing  100095
   China

   Email: c.l@huawei.com



Authors' Addresses

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

   Email: dhruv.ietf@gmail.com


   Adrian Farrel
   Old Dog Consulting

   Email: adrian@olddog.co.uk









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

   Email: lizhenbin@huawei.com












































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