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Juniper Exam JN0-351 Topic 7 Question 42 Discussion

Actual exam question for Juniper's JN0-351 exam
Question #: 42
Topic #: 7
[All JN0-351 Questions]

Exhibit.

Which router will become the OSPF BDR if all routers are powered on at the same time?

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Suggested Answer: A

OSPF DR/BDR election is a process that occurs on multi-access data links. It is intended to select two OSPF nodes: one to be acting as the Designated Router (DR), and another to be acting as the Backup Designated Router (BDR). The DR and BDR are responsible for generating network LSAs for the multi-access network and synchronizing the LSDB with other routers on the same network1.

The DR/BDR election is based on two criteria: the OSPF priority and the router ID. The OSPF priority is a value between 0 and 255 that can be configured on each interface participating in OSPF. The default priority is 1. A priority of 0 means that the router will not participate in the election and will never become a DR or BDR. The router with the highest priority will become the DR, and the router with the second highest priority will become the BDR. If there is a tie in priority, then the router ID is used as a tie-breaker. The router ID is a 32-bit number that uniquely identifies each router in an OSPF domain. It can be manually configured or automatically derived from the highest IP address on a loopback interface or any active interface2.

In this scenario, all routers have the same priority of 1, so the router ID will determine the outcome of the election. The router IDs are shown in the exhibit as RID values. The highest RID belongs to R4 (10.10.10.4), so R4 will become the DR. The second highest RID belongs to R3 (10.10.10.3), so R3 will become the BDR.


1: OSPF DR/BDR Election: Process, Configuration, and Tuning 2: OSPF Designated Router (DR) and Backup Designated Router (BDR)

Contribute your Thoughts:

Fidelia
8 days ago
That's a good point, I didn't consider the priority. R2 could be the BDR then.
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Carin
14 days ago
I disagree, I believe R2 will become the OSPF BDR because it has the highest priority.
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Ming
16 days ago
R4 is the largest router, so it must be the OSPF BDR. Gotta go with option A!
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Fidelia
21 days ago
I think it will be R4 because it has the highest router ID.
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Lyla
23 days ago
If all routers are powered on at the same time, then R2 should become the OSPF BDR. That's my guess.
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