Should the ABR be the DR or should the 2 adjacent routers on Area 0 be the DR and BDR?

[blue phoenix]

Hi all,

Hope anyone can shed light on the matter?  Please see the image I have uploaded and suggest if R5 should be the DR or should it be R3 and R4 the BDR?

[Eugene Khabarov · Accepted solution]

If R3 and R5 on links F2/0 are in 192.168.10.0/30 subnet, it is no matter who will be DR, furthermore you can configure this link as point-to-point and get rid of DR election at all.  If no loopbacks or router-id specifically configured - R3 will be DR (in case if both routers started at the same time) based on highest active ip address. R5 will be BDR.

The same apply for R4 - R5 F3/0 connection on 192.168.10.4/30 R4 will be DR based on highest active ip address configured (if no loopbacks or router-id specified). R5 will be BDR. 

[LJ Gabrillo · Accepted solution]

Hi There,

This is what I take note with regards to DR/BDR Election:

DR Election

1. Highest interface Priority

2. Highest Router ID

        2.1 Hardcoded Router-ID

        2.2 Highest Loopback Interface IP

        2.3 Highest Interface IP

BDR Election:
-Second best of DR

Just note that the purpose of the DR:

DR help maintain and manage adjacency

-Avoid high CPU and memory utilization

-Avoid unnecessary traffic due to hello packets

-BDR takes over if DR fails, BDR becomes new DR and BDR election occurs

That's its purpose, It wont improve greatly the path your packet goes or related. Just optimizes all your routers to not over use its CPU

And also, election happens after adjacency, 

->Re-election must occur before new DR is elected. Point is, even if you have a new router added, the existing DR will still exist. To cope with that do: #clear ip ospf process IN THE DR

To verify DR do: #show ip ospf neigbor -Execute it in your ABR considering it has the most neighbors, the one marked with DR is well, the DR