| PCE Working Group | U. Palle |
| Internet-Draft | D. Dhody |
| Intended status: Standards Track | Huawei Technologies |
| Expires: July 29, 2014 | January 25, 2014 |
PCEP Extensions for PCE-initiated Point-to-Multipoint LSP Setup in a Stateful PCE Model
draft-palle-pce-stateful-pce-initiated-p2mp-lsp-00
The Path Computation Element (PCE) has been identified as an appropriate technology for the determination of the paths of point-to-multipoint (P2MP) TE LSPs. The extensions described in [I-D.ietf-pce-stateful-pce] provide stateful control of Multiprotocol Label Switching (MPLS) Traffic Engineering Label Switched Paths (TE LSP) via PCE communication Protocol (PCEP), for a model where the Path Computation Client (PCC) delegates control over one or more locally configured LSPs to the PCE. Further [I-D.ietf-pce-pce-initiated-lsp] describes the creation and deletion of PCE-initiated LSPs under the stateful PCE model. This document provides extensions required for PCEP so as to enable stateful PCE-Initiated point-to-multipoint (P2MP) TE LSP instantiation.
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As per [RFC4655], the Path Computation Element (PCE) is an entity that is capable of computing a network path or route based on a network graph, and applying computational constraints. A Path Computation Client (PCC) may make requests to a PCE for paths to be computed.
[RFC4857] describes how to set up point-to-multipoint (P2MP) Traffic Engineering Label Switched Paths (TE LSPs) for use in Multiprotocol Label Switching (MPLS) and Generalized MPLS (GMPLS) networks. The PCE has been identified as a suitable application for the computation of paths for P2MP TE LSPs ([RFC5671]).
The PCEP is designed as a communication protocol between PCCs and PCEs for point-to-point (P2P) path computations and is defined in [RFC5440]. The extensions of PCEP to request path computation for P2MP TE LSPs are described in [RFC6006].
Stateful PCEs are shown to be helpful in many application scenarios, in both MPLS and GMPLS networks, as illustrated in [I-D.ietf-pce-stateful-pce-app]. These scenarios apply equally to P2P and P2MP TE LSPs. [I-D.ietf-pce-stateful-pce] provides the fundamental extensions needed for stateful PCE to support general functionality for P2P TE LSP. Further [I-D.palle-pce-stateful-pce-p2mp] focuses on the extensions that are necessary in order for the deployment of stateful PCEs to support P2MP TE LSPs. It includes mechanisms to effect P2MP LSP state synchronization between PCCs and PCEs, delegation of control of P2MP LSPs to PCEs, and PCE control of timing and sequence of P2MP path computations within and across PCEP sessions and focuses on a model where P2MP LSPs are configured on the PCC and control over them is delegated to the PCE.
[I-D.ietf-pce-pce-initiated-lsp] provides the fundamental extensions needed for stateful PCE-initiated P2P TE LSP instantiation.
This document describes the setup, maintenance and teardown of PCE- initiated P2MP LSPs under the stateful PCE model, without the need for local configuration on the PCC, thus allowing for a dynamic network that is centrally controlled and deployed.
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 [RFC2119].
Terminology used in this document is same as terminology used in [I-D.ietf-pce-stateful-pce], [I-D.ietf-pce-pce-initiated-lsp] and [RFC6006].
[I-D.palle-pce-stateful-pce-p2mp] provides stateful control over P2MP TE LSPs that are locally configured on the PCC. This model relies on the Ingress taking an active role in delegating locally configured P2MP TE LSPs to the PCE, and is well suited in environments where the P2MP TE LSP placement is fairly static. However, in environments where the P2MP TE LSP placement needs to change in response to application demands, it is useful to support dynamic creation and tear down of P2MP TE LSPs. The ability for a PCE to trigger the creation of P2MP TE LSPs on demand can be seamlessly integrated into a controller-based network architecture, where intelligence in the controller can determine when and where to set up paths.
Section 3 of [I-D.ietf-pce-pce-initiated-lsp] further describes the motivation behind the PCE-Initiated capability, which are equally applicable for P2MP TE LSPs instantiation.
A PCC or PCE indicates its ability to support PCE provisioned dynamic LSPs and P2MP operations during the PCEP Initialization Phase via mechanism described in Section 4.
As per section 5.1 of [I-D.ietf-pce-pce-initiated-lsp], the PCE sends a Path Computation LSP Initiate Request (PCInitiate) message to the PCC to instantiate or delete a P2P TE LSP. This document extends the PCInitiate message to support P2MP TE LSP Instantiation (see details in Section 5.1).
P2MP TE LSP instantiation and deletion operations are same as P2P LSP Instantiation as described in section 5.3 and 5.4 of [I-D.ietf-pce-pce-initiated-lsp]. This document focuses on extensions needed for further handling of P2MP TE LSP Instantiation (see details in Section 5.2).
As per Section 3.1 of [RFC6006], PCE advertises P2MP capability via IGP discovery or a P2MP capable TLV in open message. To support instantiation of PCE-initiated P2MP TE LSPs, this document extends the advertisement of P2MP capable TLV in open message by all PCEP speakers. As per Section 4 of [I-D.ietf-pce-pce-initiated-lsp], PCC or PCE advertises capability for instantiation of PCE-initiated LSPs via Stateful PCE Capability TLV (LSP-INSTANTIATION-CAPABILITY bit) in open message. These mechanism when used together indicates the instantiation capability for P2MP TE LSPs by the PCEP speaker.
As defined in section 5.1 of [I-D.ietf-pce-pce-initiated-lsp], PCE sends a PCInitiate message to a PCC to instantiate a P2P TE LSP, this document extends the format of PCInitiate message for the creation of P2MP TE LSPs but the creation and deletion operations of P2MP TE LSP are same to the P2P TE LSP.
The format of PCInitiate message is 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-point-path-pair-list>
[<attribute-list>]
<PCE-initiated-lsp-deletion> ::= <SRP>
<LSP>
Where:
<end-point-path-pair-list>::=
[<END-POINTS>]
<path>
[<end-point-path-pair-list>]
<path> ::= (<ERO>|<SERO>)
[<path>]
<attribute-list> is defined in [RFC5440] and extended
by PCEP extensions.
Figure 1
The PCInitiate message with an LSP object with N bit (P2MP) set is used to convey operation on a P2MP TE LSP. The SRP object is used to correlate between initiation requests sent by the PCE and the error reports and state reports sent by the PCC as described in [I-D.ietf-pce-stateful-pce].
The Instantiation operation of P2MP TE LSP is same as defined in section 5.3 of [I-D.ietf-pce-pce-initiated-lsp]. Rules of processing and error codes remains unchanged. Further, as defined in section 6.1 of [I-D.palle-pce-stateful-pce-p2mp], N bit MUST be set in LSP object in PCInitiate message by PCE to specify the instantiation is for P2MP TE LSP and the PCC or PCE MUST follow the mechanism defined in [I-D.palle-pce-stateful-pce-p2mp] for delegation and updation of P2MP TE LSPs.
The deletion operation of P2MP TE LSP is same as defined in section 5.4 of [I-D.ietf-pce-pce-initiated-lsp] by sending an LSP Initiate Message with an LSP object carrying the PLSP-ID of the LSP to be removed and an SRP object with the R flag set (LSP-REMOVE as per section 5.2 of [I-D.ietf-pce-pce-initiated-lsp]). Rules of processing and error codes remains unchanged.
P2MP TE LSP delegation and cleanup operations are same as defined in section 6 of [I-D.ietf-pce-pce-initiated-lsp]. Rules of processing and error codes remains unchanged.
The total PCEP message length, including the common header, is 16 bytes. In certain scenarios the P2MP LSP Initiate may not fit into a single PCEP message (initial PCInitiate message). The F-bit is used in the LSP object to signal that the initial PCInitiate was too large to fit into a single message and will be fragmented into multiple messages.
Fragmentation procedure described below for PCInitiate message is similar to [RFC6006] which describes request and response message fragmentation.
Once the PCE initiates to set up the P2MP TE LSP, a PCInitiate message is sent to the PCC. If the PCInitiate is too large to fit into a single PCInitiate message, the PCE will split the PCInitiate over multiple messages. Each PCInitiate message sent by the PCE, except the last one, will have the F-bit set in the LSP object to signify that the PCInitiate has been fragmented into multiple messages. In order to identify that a series of PCInitiate messages represents a single Initiate, each message will use the same PLSP-ID (in this case 0) and SRP-ID-number.
[Editor Note: P2MP message fragmentation errors associated with a P2MP path initiation will be defined in future version].
The PCEP protocol extensions described in this document for PCC or PCE with instantiation capability for P2MP TE LSPs MUST NOT be used if PCC or PCE has not advertised its stateful capability with Instantiation and P2MP capability as per Section 4. If this is not the case and Stateful operations on P2MP TE LSPs are attempted, then a PCErr with error-type 19 (Invalid Operation) and error-value TBD needs to be generated.
[Editor Note: more information on exact error value is needed]
TBD
TBD.
TBD.
TBD.
TBD.
TBD.
TBD.
TBD
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. |