PCEP Extensions for traffic steering support in Service Function Chaining
draft-wu-pce-traffic-steering-sfc-05

Abstract

This document provides an overview of the usage of Path Computation Element (PCE) with Service Function Chaining (SFC); which is described as the definition and instantiation of an ordered set of such service functions (such as firewalls, load balancers), and the subsequent "steering" of traffic flows through those service functions.

This document specifies extensions to the Path Computation Element Protocol (PCEP) that allow a stateful PCE to compute and instantiate Service Function Paths (SFP).

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Table of Contents

• 1. Introduction
• 2. Conventions used in this document
• 3. Service Function Paths and PCE
• 4. Overview of PCEP Operation in SFC-enabled Networks
• 4.1. SFP Instantiation
• 4.2. SFP Withdrawal
• 4.3. SFP Delegation and Cleanup
• 4.4. SFP State Synchronization
• 4.5. SFP Update and Report
• 5. Object Formats
• 5.1. The OPEN Object
• 5.2. The LSP Object
• 5.2.1. SFP Identifiers TLV
• 6. Backward Compatibility
• 7. Relationship to SR
• 8. Security Considerations
• 9. IANA Considerations
• 10. References
• 10.1. Normative References
• 10.2. Informative References

1. Introduction

Service chaining enables the creation of composite services that consist of an ordered set of Service Functions (SF) that must be applied to packets and/or frames selected as a result of classification as described in [I-D.ietf-sfc-architecture] and referred to as Service Function Chain (SFC). A Service Function Path (SFP) is the instantiation of a SFC in the network. Packets follow a Service Function Path from a classifier through the requisite Service Functions (SF).

[RFC5440] describes the Path Computation Element Protocol (PCEP) as the communication between a Path Computation Client (PCC) and a Path Control Element (PCE), or between PCE and PCE, enabling computation of Multiprotocol Label Switching (MPLS) for Traffic Engineering Label Switched Path (TE LSP).

[I-D.ietf-pce-stateful-pce] specifies extensions to PCEP to enable stateful control of MPLS TE LSPs. [I-D.ietf-pce-pce-initiated-lsp] provides the fundamental extensions needed for stateful PCE-initiated LSP instantiation.

This document specifies extensions to the PCEP that allow a stateful PCE to compute and instantiate Service Function Paths (SFP).

2. Conventions used in this document

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 [RFC2119].

The following terminologies are used in this document:

PCC:

Path Computation Client.

PCE:

Path Computation Element.

PCEP:

Path Computation Element Protocol.

PDP:

Policy Decision Point.

SF:

Service Function.

SFC:

Service Function Chain.

SFP:

Service Function Path.

SFF:

Service Forwarder Function.

UNI:

User-Network Interface.

3. Service Function Paths and PCE

Services are constructed as a sequence of SFs that represent an SFC, where a SF can be a virtual instance or be embedded in a physical network element, and one or more SFs may be supported by the same physical network element. A SFC creates an abstracted view of a service and specifies the set of required SFs as well as the order in which they must be executed.

When an SFC is instantiated into the network it is necessary to select the specific instances of SFs that will be used, and to create the service topology for that SFC using SF network locators. Thus, instantiation of the SFC results in the creation of a Service Function Path (SFP) and is used for forwarding packets through the SFC. In other words, an SFP is the instantiation of the defined SFC as described in [I-D.ietf-sfc-architecture].

The selection of SFP can be based on a set of policy attributes (forwarding and routing, QoS, security, etc., or a combination thereof), ranging from simple to more elaborate selection criteria and the use of stateful PCE with extensions to PCEP are one such way to achieve this.

Stateful pce [I-D.ietf-pce-stateful-pce] specifies a set of extensions to PCEP to enable stateful control of TE LSPs. [I-D.ietf-pce-pce-initiated-lsp] provides the fundamental motivations and extensions needed for stateful PCE-initiated LSP instantiation. This document specifies extensions that allow a stateful PCE to compute and instantiate Service Function Paths (SFP) via PCEP.

              +------------------------+
              |           stateful PCE |
              |  +-------+  +-------+  |
              |  |Policy |  | TE-DB |  |    +-------+
              |  +-------+  +-------+  |    |  SFC  |
   +----------|      +-------------+   |<---|control|
   |SFP       |      |LSP-DB/SFP-DB|   |    | plane |
   |Instan-   |      +-------------+   |    +-------+
   |tiation   +------------------------+
   |            +-----+ +-----+          +-----+
   |            |SF-1 | |SF-2 |          |SF-3 |
   |            |     | |     |          |     |
   |            +---+-+ +-+---+          +--+--+
   |                |     |                 |
   |               ++-----++           +----+--+
   V               |       |           |       |
+-----+  Signaling |       | Signaling |       | Signaling
| SF  |----------->| SFF-1 | --------->| SFF-2 |----------->
Classifier         |       |           |       |
|Node |            |       |           |       |
+-----+            +-------+           +-------+
                      

 
 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=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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                PLSP-ID                | Flags |F|C|  O|A|R|S|D|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
//                        TLVs                                 //
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+