Versatile Routing and Services with BGP: Understanding and Implementing BGP in SR-OS

Chapter 4

BGP Signaling for VPWS

The widely adopted method for setup, maintenance, and teardown of pseudowires using LDP for signaling is defined in RFC 4447. However, it is equally possible to use BGP for Auto-Discovery and Signaling of point-to-point L2-VPNs using much of the mechanics previously described for VPLS with some additional concepts from RFC 6624. Although individual sections of this book are readable in their own right, the overlap with BGP-VPLS is significant and many of the concepts are not repeated in this chapter. Therefore, readers of this chapter should read Chapter 3 as well.

BGP VPWS

The SR-OS implementation of BGP VPWS supports Ethernet pseudowires and provides for a redundant access capability using BGP Multi-Homing (draft-ietf-l2vpn-vpls-multihoming). It provides two options:

• Establishing a single pseudowire to the DF of a Site-ID
• Signaling two pseudowires to the DF/non-DF in an active/standby arrangement

The active/standby method provides faster reconvergence upon failure than the single pseudowire method, primarily because the standby pseudowire is presignaled. The single pseudowire method can be considered a subset of that capability and aligns with the implementations supported by other vendors.

The VPLS NLRI with AFI (25) and VPLS SAFI (65) used for Auto-Discovery and Signaling of VPLS services is extended for the VPWS NLRI to include a Circuit Status Vector (CSV) encoded as a TLV. The type field of this TLV is 1 and the value field uses a bit-vector ...