This section describes the application of BGP multihoming to I-VPLS services. BGP multihoming for I-VPLS uses the same mechanisms as those used when BGP multihoming is configured in a non-PBB VPLS service, which are described in detail in this guide.
The multihomed sites can be configured with either a SAP or spoke-SDP, and support both split horizon groups and fate-sharing by the use of oper-groups.
When the B-VPLS service is using LDP signaled pseudowires, blackhole protection is supported after a multihoming failover event when send-flush-on-failure and send-bvpls-flush flush-all-from-me is configured within the I-VPLS. This causes the system on which the site object fails to send a MAC flush all-from-me message so that customer MACs are flushed on the remote backbone edge bridges using a flush-all-from-me message. The message sent includes a PBB TLV which contains the source B-MAC identifying the originator (‟mine”/‟me”) of the flush indication and the ISID list identifying the I-VPLS instances affected by the flush indication, see section LDP MAC flush solution for PBB blackholing.
The VPLS preference sent in BGP multihoming updates is always set to zero, however, if a non-zero value is received in a valid BGP multihoming update it is used to influence the designated forwarder (DF) election.