The query here is what is selected first: The DR or the BDR?
From the selection process, it seems that the BDR is selected first and then DR. If there is no DR present, then the BDR becomes the DR.
My second question is, how do the routers vote to become a DR or a BDR?
Jeff Doyle in his book says that some routers claim to be DRs and some for being a BDR. How?
Awaiting a reply.
-/ Kiran Cherian
>> this process will be done for all the routers in a particular area,
Actually, DR and BDR election is performed on each LAN segment: if there 4 Vlans then 4 DRs and 4 BDRs are elected.
to take part in election and to build adjacencies with the elected DR and BDR all routers must agree on some parameters that are present in Hello packets:
Area-id: a 4 byte value
Area flag: = type of area
Authentication: if used must match
OSPF router-id have to be unique to avoid problems.
So in an OSPF area many DRs and BDRs can exist.
The usage of ip ospf priority is recommended to avoid to have the same router acting as DR in multiple LAN segments that will increase its CPU load.
(without changing priority the highest OSPF RID will win in all LAN interfaces it is heard by other routers)
The suggestion is to distribute the workload of DR and BDR roles on different routers.
The DR will build a Network LSA (type 2) to describe the multiaccess segment that includes a list of OSPF RIDs of routers that are connected to the LAN.
This allows distant routers in the same OSPF area to know the topology in detail.
Hope to help