DR selection in a common ethernet link

[ashres]

If R1 and R2 are in the same Ethernet link, according to the following exhibit, R1 should be DR. However, the exhibit mentions different DR in each router. 

Isn't there supposed to be one DR per link?

[Georg Pauwen]

Hello,

check the process IDs on your routers, they need to be the same. You have:

R1

router ospf 1

R2

router ospf 2

[Peter Paluch]

Hello Georg,

I respectfully disagree - it is EIGRP that requires that neighboring routers have the same process number. OSPF does not advertise the process number in its packets, and so does not depend on whether the neighbors use the same process number.

However, from the output (and this seems to be a test question), the timers are mismatched between the neighbors. OSPF requires the timers (Hello and Dead intervals) to be identical, otherwise, the routers will ignore each other. I guess that this is the reason why there are two DRs on this segment, one ignoring the other.

Best regards,
Peter

[Georg Pauwen]

Peter,

yes, you are absolutely right, and I was absolutely wrong. That looked like an easy answer...it wasn't...(:

I missed that this apparently is an exam question. I guess in a real network you would notice right away that no OSPF neighborships are established...

[ashres]

Yes, it is an exam question. 

The graphic shows the output of the show ip ospf interface e0 command for routers R1 and R2. Based on the information in the graphic, what is the cause of this problem?

A. The OSPF area is not configured properly.
B. The priority on R1 should be set higher.
C. The cost on R1 should be set higher.
D. The hello and dead timers are not configured properly.
E. A backup designated router needs to be added to the network.
F. The OSPF process ID numbers must match.

I have noticed the difference in hello and dead timers. I would build a lab to check if there are two DRs on the same ethernet link due to this difference.

[Deepak Kumar]

Hi,

OSPF will not check your process number. So there is no impact of process ID. I can see that your Hello timer, dead timer are not same. This is a big reason in OSPF.

Regards,

Deepak Kumar