I am tasked with migrating a network from EIGRP to OSPF. My thought is that I would start configuring OSPF on the exterior and work my way to the core. That being said my end goal is that the core be the designated router. I am worried that if I start enabling OSPF on the exterior first then another router would become the designated router before I get to the core, even if I configure the core with a higher OSPF priority due to the fact that an OSPF DR has already been elected. I know that once I get to the core I can start shutting interfaces and restarting the OSPF process to force the core to be the DR but I really do not want to go that route.
My current idea is that I figure all exterior routers with an OSPF priority of 0 then once I get to the core configure that with an OSPF priority of 2 then the routes will be learned and the core will be the designated router.
My only worry is that if I set all of the exterior routers with a priority of 0 will they still form neighbor relationships with each other and then cause redundant traffic to be passed around the network until I configure the core due to the fact that there is no designated router?
Additionally, if I go this way then there will never be a backup designated router. How important is it to actually have one of your routers be elected as BDR in OSPF?
