DR (default router) and DBR question?!!!

kruegerbeats

Router A has the lowest IP on the 10.4.0.0/16 network, and is elected the DR.
Router A has the lowest IP on the 10.5.0.0/16 network, and is not elected the DR.
Am I missing something? I thought the highest IP number was used to determine the DR since the default OSPF settings were used?
Please help.

chap11-2.jpg

Zoovash

Since the default OSPF settings are used and no priority is set, the election is using the highest RID to make the selection. The RID (Router ID) is the highest logical (loopback) IP address configured on a router, if no logical/loopback IP address is set then the router uses the highest IP address configured on its active interfaces. The consequence is that the RID can be different than the IP for a specific segment. In your example, since there's no loopback interface configured, Router A has a RID of 10.5.0.1 and is elected DR for 10.4.0.0/16 network because is higher than the RID of HQ Router which is 10.4.0.2.

Hope this helps!