BGP Dual Homing – Dual Homing WAN Circuits with BGP


we have the following scenario:

MPLS_WAN_provider1 connects to our edge router1 via eBGP
MPLS_WAN_provider2 connects to our edge router2 via eBGP

Both edge routers are to connect to our LAN. We need to decide on a routing protocol, between our LAN and both edge routers, that will support rerouting should one of the MPLS circuits go down.

We are considering either OSPF or iBGP, can both do the failover re-routing?

What are the advantages of one routing protocol over the other?

Best Answer

You probably want to run iBGP between your WAN routers, but make sure you have a direct link between the WAN routers. There are failure scenarios where not having the direct link can cause prefixes to be blackholed, especially if you run iBGP to other routers on the LAN..

You can use either iBGP or OSPF for you LAN routers, but iBGP requires a full mesh or a mitigation (route reflectors or confederations). That is because an iBGP speaker cannot advertise an iBGP learned prefix to another iBGP speaker. This is often not appropriate because it can limit your LAN topology.

You can run OSPF without the full mesh limitation of iBGP, and you could use a single or multiple areas, whichever is most appropriate for your site.