Network Working Group D. Dhody
Internet-Draft Huawei Technologies
Intended status: Standards Track A. Farrel
Expires: February 8, 2020 Old Dog Consulting
Z. Li
Huawei Technologies
August 7, 2019

PCEP Extension for Flow Specification


The Path Computation Element (PCE) is a functional component capable of selecting the 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

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 February 8, 2020.

Copyright Notice

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

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents ( 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

[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 of as traffic flow specifications (Flow Specifications) was introduced for BGP in [RFC5575] and updated (for clarification) in [RFC7674]. A Flow 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 in during 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:

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.

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:

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. 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 the 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 even though 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. 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 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:

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 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              |


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.


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

 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 -

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).

Following TLVs can be used in the FLOWSPEC object:

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 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 to be used in PCEP.

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 description 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.

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 on to 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.

| 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

This document defines following new types -

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 a 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.

 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 are as described in Section 4.9.1 of [RFC7761] noting that the two address fields are 32 bits for the IPv4 Multicast Flow and 128 bits for the IPv6 Multicast Flow. The Reserved field MUST be set to zero and ignored on receipt.

Two 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 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:

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.

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 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 prioritise 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 prioritised 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.

9. PCEP Messages

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> ::= <PCE-initiated-lsp-request>

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

   <PCE-initiated-lsp-instantiation> ::= <SRP>

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

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

<PCUpd Message> ::= <Common Header>

   <update-request-list> ::= <update-request>

   <update-request> ::= <SRP>

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

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

      <path>::= <intended-path>

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

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

   <request>::= <RP>

      <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>



      <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 "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:

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:

Value   | Meaning                      | Reference
 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:

 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".

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 to protect 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].

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:

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, an 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 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 just 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 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 an 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 travelling 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.

13.8. Other Considerations

No other manageability considerations are known at this time.

14. Acknowledgements

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

15. References

15.1. Normative References

[I-D.ietf-idr-flow-spec-v6] McPherson, D., Raszuk, R., Pithawala, B.,, a. and S. Hares, "Dissemination of Flow Specification Rules for IPv6", Internet-Draft draft-ietf-idr-flow-spec-v6-09, 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.
[RFC4760] Bates, T., Chandra, R., Katz, D. and Y. Rekhter, "Multiprotocol Extensions for BGP-4", RFC 4760, DOI 10.17487/RFC4760, January 2007.
[RFC5440] Vasseur, JP. and JL. Le Roux, "Path Computation Element (PCE) Communication Protocol (PCEP)", RFC 5440, DOI 10.17487/RFC5440, March 2009.
[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.
[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.
[RFC7674] Haas, J., "Clarification of the Flowspec Redirect Extended Community", RFC 7674, DOI 10.17487/RFC7674, October 2015.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017.
[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.

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", Internet-Draft draft-ietf-idr-flowspec-l2vpn-11, 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)", Internet-Draft draft-ietf-pce-pcep-yang-12, July 2019.
[I-D.ietf-pce-segment-routing] Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W. and J. Hardwick, "PCEP Extensions for Segment Routing", Internet-Draft draft-ietf-pce-segment-routing-16, March 2019.
[I-D.ietf-teas-yang-path-computation] Busi, I. and S. Belotti, "Yang model for requesting Path Computation", Internet-Draft draft-ietf-teas-yang-path-computation-06, July 2019.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February 2006.
[RFC4655] Farrel, A., Vasseur, J. and J. Ash, "A Path Computation Element (PCE)-Based Architecture", RFC 4655, DOI 10.17487/RFC4655, August 2006.
[RFC5088] Le Roux, JL., Vasseur, JP., Ikejiri, Y. and R. Zhang, "OSPF Protocol Extensions for Path Computation Element (PCE) Discovery", RFC 5088, DOI 10.17487/RFC5088, January 2008.
[RFC5089] Le Roux, JL., Vasseur, JP., Ikejiri, Y. and R. Zhang, "IS-IS Protocol Extensions for Path Computation Element (PCE) Discovery", RFC 5089, DOI 10.17487/RFC5089, January 2008.
[RFC5886] Vasseur, JP., 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.
[RFC6123] Farrel, A., "Inclusion of Manageability Sections in Path Computation Element (PCE) Working Group Drafts", RFC 6123, DOI 10.17487/RFC6123, February 2011.
[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.
[RFC7399] Farrel, A. and D. King, "Unanswered Questions in the Path Computation Element Architecture", RFC 7399, DOI 10.17487/RFC7399, October 2014.
[RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., Parekh, R., Zhang, Z. and L. Zheng, "Protocol Independent Multicast - Sparse Mode (PIM-SM): Protocol Specification (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 2016.
[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.
[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.
[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.
[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.
[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.
[RFC8283] Farrel, A., Zhao, Q., 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.

Appendix A. Contributors

Huawei Technologies
Divyashree Techno Park,
Whitefield Bangalore,


Qiandeng Liang
Huawei Technologies
101 Software Avenue,
Yuhuatai District


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


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


Xia Chen
Huawei Technologies
Huawei Bld., No.156 Beiqing Rd.


Shunwan Zhuang
Huawei Technologies
Huawei Bld., No.156 Beiqing Rd.


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



Authors' Addresses

Dhruv Dhody Huawei Technologies Divyashree Techno Park, Whitefield Bangalore, Karnataka, 560066 India EMail:
Adrian Farrel Old Dog Consulting EMail:
Zhenbin Li Huawei Technologies Huawei Bld., No.156 Beiqing Rd. Beijing, 100095 China EMail: