This section describes the application of BGP multi-homing to I-VPLS services. BGP multi-homing for I-VPLS uses the same mechanisms as those used when BGP multi-homing is configured in a non-PBB VPLS service, which are described in detail in this guide.
The multi-homed 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 multi-homing 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 multi-homing updates is always set to zero, however, if a non-zero value is received in a valid BGP multi-homing update it is used to influence the designated forwarder (DF) election.