Introduction

[RFC6718] describes the framework and requirements for pseudowire (PW) redundancy, and [RFC6870] specifies a PW redundancy mechanism for scenarios where a set of redundant PWs are configured between Provider Edge (PE) nodes in Single-Segment Pseudowire (SS-PW) [RFC3985] applications, or between Terminating Provider Edge (T-PE) nodes in Multi-Segment Pseudowire (MS-PW) [RFC5659] applications.

In some MS-PW scenarios, there are benefits of providing PW redundancy on Switching Provider Edges (S-PEs), such as reducing the burden on the access T-PE nodes and enabling faster protection switching compared to the end-to-end MS-PW protection mechanisms.

This document describes some scenarios in which PW redundancy is provided on S-PEs and specifies the operations of the S-PEs. The S-PEs connect to the neighboring T-PEs or S-PEs with PW segments. For the S-PE that provides PW redundancy for an MS-PW, there is a single PW segment on one side, which is called the single-homed side, and there are multiple PW segments on the other side, which is called the multi-homed side. The scenario in which the S-PE has two multihomed sides is out of scope. Signaling of the Preferential Forwarding status as defined in [RFC6870] and [RFC6478] is reused. This document does not require any change to the T-PEs of MS-PW.

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].