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Configuring Multihoming on a VPLS Border Router

 

Configuring multihoming on VPLS border routers ensures that if one border router is unreachable, BGP/LDP PE connectivity is maintained through the other VPLS border router. With multihoming, one border router is chosen as the designated forwarder for each mesh group. The designated forwarder is chosen through either the BGP or VPLS path-selection procedure. If the designated forwarder loses connectivity with a mesh group, the alternate border router then takes over as designated forwarder for that mesh group. A VPLS instance must be configured with BGP signaling in order for multihoming to work.

Figure 1 shows a simplified example of how multihoming works with VPLS border routers. In this example, B1 is the designated forwarder and B2 is the alternate forwarder. If CE1 wanted to send data to CE9, the data would travel from CE1 to PE1, which is part of the LDP-1 mesh group. PE1 would then flood the data to B1 (the designated forwarder), which would forward the data to PE2. It would not send the data to Router B2. PE2 would then send the data to its destination, CE9. If B1 lost connectivity with the LDP-1 mesh group, then B2 would become the designated forwarder. In this case, PE1 would send the data through B2, not through B1.

Figure 1: Multihoming for Border Area Routers
Multihoming for Border Area Routers

You configure multihoming on border routers by including the site-identifier and multi-homing statements at the [edit routing-instances routing-instance-name protocols] hierarchy level. The designated forwarder and alternate forwarder must be configured with the same site identifier.

Router B1

Router B2

For more information on multihoming, see Option: Configuring VPLS Multihoming with BGP Signaling.