DRs and BDRs

[djcpisani]

Which one of these is the DR/s or BDR/s. Would there be more than one DR in this topology? and is this topology three seperate networks, or one? 

[Nagendra Kumar Nainar]

Hi,

DR/BDR is per broadcast subnet. In simple words if a router have 2 Ethernet interfaces with OSPF enabled (with default network type), it will have DR/BDR election in both the interfaces. It might also be posisble that the router is DR in one interface while DROther in other interafce.

In your topology, RTA will have DR/BDR election happening on 2 interfaces (10.4.0.1 and 10.5.0.1) while RTB will have DR/BDR election happening on 1 interface (10.5.0.2).

Regarding the DR/BDR selection, it uses OSPF priority or RID (if priority is same) to elect DR/BDR. 

-Nagendra

[davrojas]

Hello djcpisani,

Just to add a little some, the Point-to-Point link does not elect a DR/BDR because there are only two devices therefore there is no need for this, however you can change this behavior (which would be non-nonsensical in real world) by changing the opsf interface type.

Regards,

D_-a-_v_-i-_D