[Docs] [txt|pdf|xml|html] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits] [IPR]

Versions: (draft-li-pce-pcep-flowspec) 00 01 02 03 04 05 06

Network Working Group                                           D. Dhody
Internet-Draft                                       Huawei Technologies
Intended status: Standards Track                               A. Farrel
Expires: May 5, 2020                                  Old Dog Consulting
                                                                   Z. Li
                                                     Huawei Technologies
                                                        November 2, 2019


                 PCEP Extension for Flow Specification
                    draft-ietf-pce-pcep-flowspec-06

Abstract

   The Path Computation Element (PCE) is a functional component capable
   of selecting paths through a traffic engineered network.  These paths
   may be supplied in response to requests for computation, or may be
   unsolicited instructions 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 5575 defines the Flow Specification and
   describes how Flow Specification Components are used to describe
   traffic flows.  RFC 5575 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.

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/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on May 5, 2020.



Dhody, et al.              Expires May 5, 2020                  [Page 1]


Internet-Draft                PCEP-FlowSpec                November 2019


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
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Procedures for PCE Use of Flow Specifications . . . . . . . .   5
     3.1.  Context for PCE Use of Flow Specifications  . . . . . . .   5
     3.2.  Elements of Procedure . . . . . . . . . . . . . . . . . .   5
       3.2.1.  Capability Advertisement  . . . . . . . . . . . . . .   6
       3.2.2.  Dissemination Procedures  . . . . . . . . . . . . . .   7
       3.2.3.  Flow Specification Synchronization  . . . . . . . . .   8
   4.  PCE FlowSpec Capability TLV . . . . . . . . . . . . . . . . .   8
   5.  PCEP FLOWSPEC Object  . . . . . . . . . . . . . . . . . . . .   9
   6.  Flow Filter TLV . . . . . . . . . . . . . . . . . . . . . . .  11
   7.  Flow Specification TLVs . . . . . . . . . . . . . . . . . . .  11
   8.  Detailed Procedures . . . . . . . . . . . . . . . . . . . . .  15
     8.1.  Default Behavior and Backward Compatibility . . . . . . .  15
     8.2.  Composite Flow Specifications . . . . . . . . . . . . . .  15
     8.3.  Modifying Flow Specifications . . . . . . . . . . . . . .  16
     8.4.  Multiple Flow Specifications  . . . . . . . . . . . . . .  16
     8.5.  Adding and Removing Flow Specifications . . . . . . . . .  16
     8.6.  VPN Identifiers . . . . . . . . . . . . . . . . . . . . .  17
     8.7.  Priorities and Overlapping Flow Specifications  . . . . .  17
   9.  PCEP Messages . . . . . . . . . . . . . . . . . . . . . . . .  18
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  21
     10.1.  PCEP Objects . . . . . . . . . . . . . . . . . . . . . .  21
       10.1.1.  PCEP FLOWSPEC Object Flag Field  . . . . . . . . . .  21
     10.2.  PCEP TLV Type Indicators . . . . . . . . . . . . . . . .  21
     10.3.  Flow Specification TLV Type Indicators . . . . . . . . .  22
     10.4.  PCEP Error Codes . . . . . . . . . . . . . . . . . . . .  22
     10.5.  PCE Capability Flag  . . . . . . . . . . . . . . . . . .  23
   11. Implementation Status . . . . . . . . . . . . . . . . . . . .  23
   12. Security Considerations . . . . . . . . . . . . . . . . . . .  24
   13. Manageability Considerations  . . . . . . . . . . . . . . . .  24



Dhody, et al.              Expires May 5, 2020                  [Page 2]


Internet-Draft                PCEP-FlowSpec                November 2019


     13.1.  Management of Multiple Flow Specifications . . . . . . .  25
     13.2.  Control of Function through Configuration and Policy . .  25
     13.3.  Information and Data Models  . . . . . . . . . . . . . .  26
     13.4.  Liveness Detection and Monitoring  . . . . . . . . . . .  26
     13.5.  Verifying Correct Operation  . . . . . . . . . . . . . .  26
     13.6.  Requirements on Other Protocols and Functional
            Components . . . . . . . . . . . . . . . . . . . . . . .  26
     13.7.  Impact on Network Operation  . . . . . . . . . . . . . .  27
     13.8.  Other Considerations . . . . . . . . . . . . . . . . . .  27
   14. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  27
   15. References  . . . . . . . . . . . . . . . . . . . . . . . . .  27
     15.1.  Normative References . . . . . . . . . . . . . . . . . .  27
     15.2.  Informative References . . . . . . . . . . . . . . . . .  28
   Appendix A.  Contributors . . . . . . . . . . . . . . . . . . . .  30
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  32

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) networks, and more recent work has brought other traffic
   engineering technologies and planning applications into scope (for
   example, Segment Routing (SR) [I-D.ietf-pce-segment-routing]).

   [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 the
   LSPs 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) was introduced for BGP in
   [RFC5575] and updated (for clarification) in [RFC7674].  A Flow



Dhody, et al.              Expires May 5, 2020                  [Page 3]


Internet-Draft                PCEP-FlowSpec                November 2019


   Specification is comprised of traffic filtering rules and actions.
   The routers that receive a Flow Specification can classify received
   packets according to the traffic filtering rules and can direct
   packets based on the 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, and 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 Specifications Components.  For convenience we
   term the description of a traffic flow using Flow Specification
   Components as a "Flow Specification" and it must be understood that
   this is not the same as the same term used in [RFC5575] since no
   action is explicitly included in the encoding.

   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 Flow Spec Object
   defined in this document.  The flow filtering rules indicated by the
   Flow Specifications are mainly defined by BGP Flow Specifications.

2.  Terminology

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

   The following term from [RFC5575] is used frequently throughout this
   document:

      Flow Specification (FlowSpec): A Flow Specification is an n-tuple
      consisting of several matching criteria that can be applied to IP
      traffic, including filters and actions.  Each FlowSpec consists of
      a set of filters and a set of actions.

   However, in the context of this document, no action is specified as
   part of the FlowSpec since the action "forward all matching traffic
   onto the associated path" is implicit.



Dhody, et al.              Expires May 5, 2020                  [Page 4]


Internet-Draft                PCEP-FlowSpec                November 2019


   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 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 which will then signal the LSP across the
       network.

   5.  Tell the head end 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.

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.




Dhody, et al.              Expires May 5, 2020                  [Page 5]


Internet-Draft                PCEP-FlowSpec                November 2019


   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 including 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.

   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 indicate support of
   the functionality described in this document by not including 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 that does not support the procedures.  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 [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.







Dhody, et al.              Expires May 5, 2020                  [Page 6]


Internet-Draft                PCEP-FlowSpec                November 2019


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
      plans to 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.

   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.




Dhody, et al.              Expires May 5, 2020                  [Page 7]


Internet-Draft                PCEP-FlowSpec                November 2019


   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.

   The PCEP FLOWSPEC Object carries zero or one Flow Filter TLV which
   describes a traffic flow.

   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].

   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.





Dhody, et al.              Expires May 5, 2020                  [Page 8]


Internet-Draft                PCEP-FlowSpec                November 2019


   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 is set to default value 0.
   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 traffic flow.

   The PCEP FLOWSPEC object carries a FlowSpec filter rule encoded in a
   TLV (as defined in Section 6).

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

   The FLOWSPEC Object-Type is 1.

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












Dhody, et al.              Expires May 5, 2020                  [Page 9]


Internet-Draft                PCEP-FlowSpec                November 2019


    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     |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.

   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): One flag is 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.

      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 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).



Dhody, et al.              Expires May 5, 2020                 [Page 10]


Internet-Draft                PCEP-FlowSpec                November 2019


   Following TLVs can be used in the FLOWSPEC object:

   o  Speaker Entity Identifier TLV: As specified in [RFC8232], 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).

   o  Flow Filter TLV (variable): One TLV MAY be included.  The Flow
      Filter TLV is OPTIONAL when the R bit is set.  The TLV MUST be
      present when the R bit is clear.  If the TLV is missing when the R
      bit is clear, the PCEP peer MUST respond with a PCErr message with
      error-type TBD8 (FlowSpec Error), error-value 2 (Malformed
      FlowSpec).

6.  Flow Filter TLV

   A new PCEP TLV is defined to convey Flow Specification filtering
   rules that specify what traffic is carried on a path.  The TLV
   follows 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.

   The Value field contains one or more sub-TLVs (the Flow Specification
   TLVs) as defined in Section 7.  Only one Flow Filter TLV can be
   present and represents the complete definition of a Flow
   Specification for traffic to be placed on the tunnel indicated by the
   PCEP message in which the PCEP Flow Spec Object is carried.  The set
   of Flow Specification TLVs in a single instance of a Flow Filter TLV
   are combined to indicate the specific Flow Specification.

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

7.  Flow Specification TLVs

   The Flow Filter TLV carries one or more Flow Specification TLV.  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) 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 [RFC5575].  This is possible
   because the BGP Flow Spec encoding uses a single octet to encode the



Dhody, et al.              Expires May 5, 2020                 [Page 11]


Internet-Draft                PCEP-FlowSpec                November 2019


   type where as PCEP uses two octets.  Thus the space of values for the
   Type field is partitioned as shown in Figure 3.


   Range          |
   ---------------+---------------------------------------------------
   0              | Reserved - must not be allocated.
                  |
   1 .. 255       | Per BGP registry defined by [RFC5575] 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

   [RFC5575] created the registry "Flow Spec Component Types" and made
   allocations to it.  [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 1..255 is as per "Flow Spec Component Types"
   [RFC5575]; if the AFI is set to IPv6, the range 1..255 is as per
   "Flow Spec IPv6 Component Types" [I-D.ietf-idr-flow-spec-v6].  When
   future BGP specifications (such as [I-D.ietf-idr-flowspec-l2vpn])
   make further allocations to the aforementioned registries, they are
   also inherited for PCEP usage.

   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
   [RFC5575] 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
   [RFC5575].

   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.





Dhody, et al.              Expires May 5, 2020                 [Page 12]


Internet-Draft                PCEP-FlowSpec                November 2019


   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 1 to 255 have
   Values defined for use in BGP (for example, in [RFC5575],
   [I-D.ietf-idr-flow-spec-v6], and [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 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.








Dhody, et al.              Expires May 5, 2020                 [Page 13]


Internet-Draft                PCEP-FlowSpec                November 2019


    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.  They have the common meanings
   for wildcarding in multicast.  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



Dhody, et al.              Expires May 5, 2020                 [Page 14]


Internet-Draft                PCEP-FlowSpec                November 2019


   NOT be set unless the S bit is also set: if a Multicast Flow
   Specification TLV is received with S bit = 0 and G bit = 1 the
   receiver SHOULD 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,
      but the Source Address prefix is ignored.

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

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 Flow Spec 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.

   [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.







Dhody, et al.              Expires May 5, 2020                 [Page 15]


Internet-Draft                PCEP-FlowSpec                November 2019


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 Flow Spec Object is used to identify a specific
   Flow Specification.

   When modifying a Flow Specification, all Flow Specification TLVs for
   the intended specification of the flow MUST be included in the PCEP
   Flow Spec Object and the FS-ID MUST be retained from the previous
   description of the flow.

8.4.  Multiple Flow Specifications

   It is possible that multiple flows will be place on a single tunnel.
   In some cases it is possible to to define these within a single PCEP
   Flow Spec Object: for example, two Destination IPv4 Prefix TLVs could
   be included to indicate that packets matching either prefix are
   acceptable.  PCEP would consider this as a single Flow Specification
   identified by a single FS-ID.

   In other scenarios the use of multiple Flow Specification TLVs would
   be confusing.  For example, if flows from A to B and from C to D are
   to be included then using two Source IPv4 Prefix TLVs and two
   Destination IPv4 Prefix TLVs would be confusing (are flows from A to
   D included?).  In these cases, each Flow Specification is carried in
   its own PCEP Flow Spec Object with multiple objects present on a
   single PCEP message.  Use of separate objects also allows easier
   removal and modification of Flow Specifications.

8.5.  Adding and Removing Flow Specifications

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

   To remove a Flow Specification, a PCEP Flow Spec 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 of the



Dhody, et al.              Expires May 5, 2020                 [Page 16]


Internet-Draft                PCEP-FlowSpec                November 2019


   Flow Specification being removed and finds a mismatch, the Flow
   Specification 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 [RFC5575].
   Section 5.1 of that document explains the order of traffic filtering
   rules to be executed by an implementation of that specification.

   PCCs MUST apply the same ordering rules as defined in [RFC5575].

   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 MUST respond with a PCErr message
   with error-type TBD8 (FlowSpec Error), error-value 3 (Unresolvable
   conflict) and MUST NOT install the Flow Specification.






Dhody, et al.              Expires May 5, 2020                 [Page 17]


Internet-Draft                PCEP-FlowSpec                November 2019


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:


   <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:














Dhody, et al.              Expires May 5, 2020                 [Page 18]


Internet-Draft                PCEP-FlowSpec                November 2019


   <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:


   <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:









Dhody, et al.              Expires May 5, 2020                 [Page 19]


Internet-Draft                PCEP-FlowSpec                November 2019


   <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>]


   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>]








Dhody, et al.              Expires May 5, 2020                 [Page 20]


Internet-Draft                PCEP-FlowSpec                November 2019


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 "FLOW SPEC
   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:

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

   o  Capability description

   o  Defining RFC

   The following values are defined in this document:


    Bit     Description           Reference

     31     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:





Dhody, et al.              Expires May 5, 2020                 [Page 21]


Internet-Draft                PCEP-FlowSpec                November 2019


   Value   | Meaning                      | Reference
   --------+------------------------------+-------------
    TBD2   | PCE-FLOWSPEC-CAPABILITY TLV  | [This.I-D]
    TBD4   | 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]:


   Range          | Assignment policy
   ---------------+---------------------------------------------------
   0              | Reserved - must not be allocated.
                  |
   1 .. 255       | Reserved - must not be allocated.
                  | Usage mirrors the BGP FlowSpec registry [RFC5575]
                  | & [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.  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:



Dhody, et al.              Expires May 5, 2020                 [Page 22]


Internet-Draft                PCEP-FlowSpec                November 2019


    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]
          |                    | 5-255: Unassigned          | [This.I-D]


10.5.  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
   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".



Dhody, et al.              Expires May 5, 2020                 [Page 23]


Internet-Draft                PCEP-FlowSpec                November 2019


   At the time of posting the -04 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], [RFC6952], and [RFC8253].

   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.

   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.
   Although this is not directly a security issue per se, the confusion
   and unexpected forwarding behavior may be engineered or exploited by
   an attacker.  Therefore, implementers and operators SHOULD pay
   careful attention to the Manageability Considerations described in
   Section 13.

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].



Dhody, et al.              Expires May 5, 2020                 [Page 24]


Internet-Draft                PCEP-FlowSpec                November 2019


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 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.

   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.

   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 support indicating 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.




Dhody, et al.              Expires May 5, 2020                 [Page 25]


Internet-Draft                PCEP-FlowSpec                November 2019


   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 will 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.

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.








Dhody, et al.              Expires May 5, 2020                 [Page 26]


Internet-Draft                PCEP-FlowSpec                November 2019


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.

13.8.  Other Considerations

   No other manageability considerations are known at this time.

14.  Acknowledgements

   Thanks to Julian Lucek, Sudhir Cheruathur, Olivier Dugeon, Jayant
   Agarwal, and Jeffrey Zhang for useful discussions.

15.  References

15.1.  Normative References

   [I-D.ietf-idr-flow-spec-v6]
              McPherson, D., Raszuk, R., Pithawala, B.,
              akarch@cisco.com, a., and S. Hares, "Dissemination of Flow
              Specification Rules for IPv6", draft-ietf-idr-flow-spec-
              v6-09 (work in progress), November 2017.

   [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>.

   [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>.







Dhody, et al.              Expires May 5, 2020                 [Page 27]


Internet-Draft                PCEP-FlowSpec                November 2019


   [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>.

   [RFC5575]  Marques, P., Sheth, N., Raszuk, R., Greene, B., Mauch, J.,
              and D. McPherson, "Dissemination of Flow Specification
              Rules", RFC 5575, DOI 10.17487/RFC5575, August 2009,
              <https://www.rfc-editor.org/info/rfc5575>.

   [RFC7674]  Haas, J., Ed., "Clarification of the Flowspec Redirect
              Extended Community", RFC 7674, DOI 10.17487/RFC7674,
              October 2015, <https://www.rfc-editor.org/info/rfc7674>.

   [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>.

   [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>.

15.2.  Informative References

   [I-D.ietf-idr-flowspec-l2vpn]
              Weiguo, H., Eastlake, D., Uttaro, J., Litkowski, S., and
              S. Zhuang, "BGP Dissemination of L2VPN Flow Specification
              Rules", draft-ietf-idr-flowspec-l2vpn-11 (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-13 (work in progress), October 2019.

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

   [I-D.ietf-teas-yang-path-computation]
              Busi, I. and S. Belotti, "Yang model for requesting Path
              Computation", draft-ietf-teas-yang-path-computation-06
              (work in progress), July 2019.



Dhody, et al.              Expires May 5, 2020                 [Page 28]


Internet-Draft                PCEP-FlowSpec                November 2019


   [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>.

   [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>.

   [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>.







Dhody, et al.              Expires May 5, 2020                 [Page 29]


Internet-Draft                PCEP-FlowSpec                November 2019


   [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>.

   [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>.

   [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>.

   [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>.

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



Dhody, et al.              Expires May 5, 2020                 [Page 30]


Internet-Draft                PCEP-FlowSpec                November 2019


   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
   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: chengli13@huawei.com




Dhody, et al.              Expires May 5, 2020                 [Page 31]


Internet-Draft                PCEP-FlowSpec                November 2019


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


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

   Email: lizhenbin@huawei.com



























Dhody, et al.              Expires May 5, 2020                 [Page 32]


Html markup produced by rfcmarkup 1.129d, available from https://tools.ietf.org/tools/rfcmarkup/