PCE Path Profiles
draft-alvarez-pce-path-profiles-04

Abstract

This document describes extensions to the Path Computation Element (PCE) Communication Protocol (PCEP) to signal path profile identifiers. A profile represents a list of path parameters or policies that a PCEP peer may invoke on a remote peer using an opaque identifier. When a path computation client (PCC) initiates a path computation request, the PCC can signal profile identifiers to invoke path parameters or policies defined on the PCE which would influence the path computation. Similarly, when a PCE initiates or updates a path, the PCE can signal profile identifiers to invoke path parameters or policies defined on the PCC which would influence the path setup.

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Table of Contents

• 1. Introduction
• 1.1. Requirements Language
• 2. Motivation
• 3. Path Profiles
• 4. Procedures
• 4.1. Capability Advertisement
• 4.2. PCC-Initiated Paths
• 4.2.1. Point-to-Point Paths
• 4.2.2. Point-to-Multipoint Paths
• 4.3. PCE-Initiated Paths
• 5. Object Extensions
• 5.1. OPEN Object
• 5.2. PATH-PROFILE Object
• 6. Error Codes for PATH-PROFILE Object
• 7. Acknowledgements
• 8. IANA Considerations
• 9. Security Considerations
• 10. References
• 10.1. Normative References
• 10.2. Informative References
• Authors' Addresses

1. Introduction

[RFC4655] specifies an architecture to address path computation requirements in large, multi-domain, multi-region and multi-layer networks. The architecture defines two main functional nodes: a path computation client (PCC) and a path computation element (PCE). It includes considerations for centralized versus distributed computation, synchronization, PCE discovery, PCE load balancing, PCE liveness detection, PCC-PCE and PCE-PCE communication, Traffic Engineering Database (TED) synchronization, stateful versus stateless PCEs, monitoring, policy, confidentiality, and evaluation metrics.

[RFC5440] specifies the PCE Protocol (PCEP) for communications between a PCC and a PCE, or between two PCEs. [I-D.ietf-pce-stateful-pce] specifies PCEP extensions for stateful control of LSPs including LSP state synchronization between PCCs and PCEs, delegation of LSP control to PCEs, and PCE control of timing and sequence of path computations within and across PCEP sessions. [I-D.ietf-pce-pce-initiated-lsp] introduces PCEP extensions to allow a stateful PCE to set up, maintain and tear down LSPs without the need for local configuration on the PCC.

This document describes PCEP extensions to signal path profile identifiers. A profile represents a list of path parameters or policies that a PCEP peer may invoke on a remote peer using an opaque identifier. The PCE may be stateful or stateless. When a path computation client (PCC) initiates a path computation request, the PCC can signal profile identifiers to invoke path parameters or policies defined on the PCE which would influence the path computation. Similarly, when a PCE initiates or updates a path, the PCE can signal profile identifiers to invoke path parameters or policies defined on the PCC which would influence the path setup.

1.1. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119].

2. Motivation

PCEP peers may need to specify request-specific parameters and policies without signaling them explicitly. The signaling of one or more path profile identifiers allows peers to make use of opaque identifiers to implicitly communicate such information. An important characteristic of this approach is that the transmitting peer does not need to know the specifics of the profiles and can invoke new functional enhancements on the receiving peer without requiring changes to its implementation.

There are multiple reasons why the explicit communication of some parameters and policies may not be possible or desirable. The transmitting peer may not implement the protocol extensions required or such extensions do not exist. The defintion of some parameters and policies may be located on the receiving peer as a matter of operational preference. The parameters and policies may not be directly related to computation or instantiation of the path, but may be related to other functionality associated with the path (e.g. traffic steering, accounting, monitoring, etc).

A PCC may use path profiles in numerous scenarios when requesting a path computation. For example, a PCE may be provisioned with a policy profile that enforces path diversity, elaborate dependencies between paths or time-based behaviors. Alternative, a PCE may be provisioned with a set of configuration profiles that define path computation parameters. These policies and configuration parameters can be centrally managed on the PCE and made effective across multiple PCCs. A PCC does not need to know the specifics of the profiles and is able to invoke new PCE functionality without changes to its implementation.

Similarly, a PCE may use path profiles in numerous scenarios when initiating or updating a path on a PCC. A PCC may be provisioned with a set of configuration and policy profiles that may be applied to paths. For example, those profiles could specify a policy to steer traffic into the path or configuration parameters related to traffic accounting, event logging, path monitoring, etc. A PCE can invoke these policies and configuration, so the PCC can establish a more completly configured path. A PCE does not need to know the specifics of the profiles and is able to invoke new PCC functionality without changes to its implementation.

3. Path Profiles

A path profile represents a list of path parameters or policies that a PCEP peer may invoke on a remote peer using a profile identifier. The receiving peer interprets the identifier according to a local path profile definition. The PATH-PROFILE object defined in Section 5.2 can signal one or more profile identifiers. PCEP carries profile identifiers as opaque values. PCEP peers do not exchange the details of a path profile.

Regarding policies in particular, the PCE path profile specifications in this document enable a new type of policy realization in the PCE architecture. They define an approach where request-specific policies may be communicated implicitly to achieve some level of coordination of policy between PCEP peers. [RFC4655] defines the current policy realization options and policy types in the PCE architecture.

4. Procedures

4.1. Capability Advertisement

PCEP peers advertise their capability to support path profile identifiers during the session initialization phase. They include the PATH-PROFILE-CAPABILITY TLV defined in Section 5.1 as part of the OPEN object. A PCEP peer can only signal path profile identifiers if both peers advertised this capability. A peer MUST send a PCErr message with Error-Type=4 (Not supported object), Error-value=1 (Not supported object class) and close the session if it receives a message with a path profile identifier, it supports the extensions in this document and both peers did not advertise this capability.

4.2. PCC-Initiated Paths

A PCC MAY include a PATH-PROFILE object when sending a PCReq message. The PCE uses the path profile identifiers to select path parameters or path policies to fulfill the request. The PCE MUST process the identifiers in the PATH-PROFILE object in the order received. The means by which the PCC learns about a particular path profile identifier and decides to include it in a PCReq message are outside the scope of this document. Similarly, the means by which the PCE selects a set of parameters or policies based on the profile identifier for a specific request are outside the scope of this document. The P flag of the PATH-PROFILE object MUST be set.

A PCE may receive a path computation request with one or more unexpected path profile identifiers. The PCE sends a PCErr message with Error-Type=[TBA] (PATH-PROFILE Error), Error-value=1 (Unknown path profile) if the path profile identifier is not known to the PCE. The PCE sends a PCErr message with Error-Type=[TBA] (PATH-PROFILE Error), Error-value=2 (Invalid path profile) if the PCE knows about the path profile identifier, but considers the request invalid. As an example, the profile may be invalid because of the path type, the PCEP session type or the originating PCC. The PCE sends a PCErr message with Error-Type=[TBA] (PATH-PROFILE Error), Error-value=3 (Incompatible path profiles) if two or more path profile identifiers are incompatible. That is, they are known and valid, but can not occur simultanously. The PCEP-ERROR object SHOULD include the path profile identifiers that generated the error condition.

The PCE will determine whether to consider any additional optional objects included in a PCReq message based on policy. As illustrated in Section 4.2.1 and Section 4.2.2, the PCC MAY include other optional objects along with a PATH-PROFILE object as part of a path computation request. The PCC will use the processing-rule (P) flag in the common object header to signal whether it considers those objects mandatory or optional when the PCE performs path computation. Those objects may overlap with the path parameters that the PCE associates with the path profile identifier.

PCE policy may place different kinds of restrictions on PCReq messages that include a PATH-PROFILE object and additional parameters. A PCE MUST send an error message if it receives a request with optional objects signaled as mandatory (P flag = 1) for path computation and PCE policy does not allow such behavior from the originating PCC. In that case, the PCE sends a PCErr message with Error-Type=[TBA] (PATH-PROFILE Error), Error-value=3 (Unexpected mandatory object). If the objects are signaled as optional (P flag = 0) for path computation, the PCE will decide based on policy whether to consider them or not. When sending the PCRep message for the request, the PCE will use the ignore (I) flag in the common object header to indicate to the PCC whether an object was ignored.

4.2.1. Point-to-Point Paths

[RFC5440] defines the basic structure of a PCReq message for point-to-point paths. This documents extends the message format as follows:

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

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

   <request>::= <RP>
                <END-POINTS>
                [<PATH-PROFILE>]
                [<path-computation>]
             
             

where:

where:

<path-computation> is the list of optional objects used for path computation as defined initially in [RFC5440] and modified in subsequent PCEP extensions.

If present in a PCReq message, the PATH-PROFILE object MUST be the first optional object in the request portion of the message.

4.2.2. Point-to-Multipoint Paths

[RFC6006] defines the basic structure of a PCReq message for point-to-multipoint paths. This documents extends the message format as follows:

<PCReq Message>::= <Common Header>
                   <request>
              
            

   <request>::= <RP>
                <end-point-rro-pair-list>
                [<PATH-PROFILE>]
                [<OF>]
                [<LSPA>]
                [<BANDWIDTH>]
                [<metric-list>]
                [<IRO>]
                [<LOAD-BALANCING>]
              
            

where:

   <end-point-rro-pair-list>::=
                      <END-POINTS>[<RRO-List>][<BANDWIDTH>]
                      [<end-point-rro-pair-list>]

   <RRO-List>::=<RRO>[<BANDWIDTH>][<RRO-List>]
   <metric-list>::=<METRIC>[<metric-list>]
              
            

where:

If present in a PCReq message, the PATH-PROFILE object MUST be the first optional object in the request portion of the message.

4.3. PCE-Initiated Paths

A PCE MAY include a PATH-PROFILE object when sending a PCInitiate message as defined in [I-D.ietf-pce-pce-initiated-lsp]. The PCC uses the path profile identifiers to select path parameters or path policies to be applied during the instantiation of the path. The PCC MUST process the identifiers in the PATH-PROFILE object in the order received. The means by which the PCE learns about a particular path profile identifier and decides to include it in a PCInitiate message are outside the scope of this document. Similarly, the means by which the PCC selects a set of parameters or policies based on the profile identifier for a specific path are outside the scope of this document.

A PCC may receive a path instantiation request with one or more unexpected path profile identifiers. The PCC sends a PCErr message with Error-Type=[TBA] (PATH-PROFILE Error), Error-value=1 (Unknown path profiles) if the path profile identifier is not known to the PCC. The PCC sends a PCErr message with Error-Type=[TBA] (PATH-PROFILE Error), Error-value=2 (Invalid path profiles) if the PCC knows about the path profile identifier, but considers the request invalid. As an example, the profile may be invalid because of the path type, the PCEP session type or the originating PCE. The PCC sends a PCErr message with Error-Type=[TBA] (PATH-PROFILE Error), Error-value=3 (Incompatible path profiles) if two or more path profile identifiers are incompatible. That is, they are known and valid, but can not occur simultanously. The PCEP-ERROR object SHOULD include the path profile identifiers that generated the error condition.

[I-D.ietf-pce-pce-initiated-lsp] defines the basic structure of a PCInitiate message. This documents extends the message format as follows:

<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>
                                        [PATH-PROFILE>
                                        [<attribute-list>]

  <PCE-initiated-lsp-deletion> ::= <SRP>
                                   <LSP>

             
             

where:

<attribute-list> is defined in [RFC5440] and extended by PCEP extensions.

5. Object Extensions

5.1. OPEN Object

This documents defines a new optional PATH-PROFILE-CAPABILITY TLV in the OPEN object.

 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=[TBA]          |            Length=4           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|            Reserved           |             Flags             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
             
             

 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               |
//                             TLVs                            //
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
             
             

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|             Type=[TBD]        |             Length=10         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|    Reserved   |      Flags    |       Path Profile Id         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|    Path Profile Id  (cont)    |         Extended Id           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|       Extended Id (cont)      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
             
             

Error-Type       Meaning                  Error-Value
  <TBA>     PATH-PROFILE Error     1: Unknown path profiles
                                   2: Invalid path profiles
                                   3: Incompatible path profiles
                                   4: Unexpected mandatory object