This section describes BGP-based procedures for electing a designated forwarder among the set of PEs that are multihomed to a customer site. Only the local PEs are actively participating in the selection algorithm. The PEs remote from the dual-homed CE are not required to participate in the designated forwarding election for a remote dual-homed CE.
The main components of the BGP-based multihoming solution for VPLS are:
Provisioning model
MP-BGP procedures
Designated Forwarder Election
Blackhole avoidance – indicating the designated forwarder change toward the core PEs and access PEs or CEs
The interaction with pseudowire signaling (BGP/LDP)
Figure 1. BGP multihoming for VPLS
Figure 1 shows the VPLS using BGP multihoming for the case of multihomed CEs. Although the figure shows the case of a pseudowire infrastructure signaled with LDP for an LDP VPLS using BGP-AD for discovery, the procedures are identical for BGP VPLS or for a mix of BGP- and LDP-signaled pseudowires.