Juniper JN0-351 Exam - Topic 4 Question 47 Discussion

Actual exam question for Juniper's JN0-351 exam

Question #: 47
Topic #: 4

You are an operator for a network running 1S-IS. Two routers are failing to form an adjacency. What are two reasons for this problem? (Choose two.)

AThere are mismatched router IDs on the L2 routers.

BThere is no configured ISO address on any IS-IS interface.

CThere is a mismatched area ID between the L2 routers.

DThe family iso configuration is missing from the adjacency interface.

Show Suggested Answer

Suggested Answer: B, D

The two reasons for the failure to form an adjacency in a network running IS-IS could be:

B) There is no configured ISO address on any IS-IS interface.IS-IS requires each router interface to have an ISO address configured.Without this address, the routers cannot form an adjacency1.

D) The family iso configuration is missing from the adjacency interface.The 'family iso' configuration is essential for IS-IS to function correctly.If this configuration is missing from the adjacency interface, it could prevent the formation of an adjacency1.

These explanations are based on the Enterprise Routing and Switching Specialist (JNCIS-ENT) documents and learning resources available at Juniper Networks23.

by Deangelo at Aug 12, 2025, 04:32 PM

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Reid

2 months ago

Missing family iso config is a big deal, can't overlook that!

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King

2 months ago

Wait, is it really possible to have no ISO address? That seems odd.

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Anissa

2 months ago

I think the area ID mismatch is a common culprit too.

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Janae

3 months ago

I disagree, I’ve seen adjacencies form without that being a problem.

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Felicidad

3 months ago

Mismatched router IDs can definitely cause issues.

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Quentin

3 months ago

I think the family iso configuration is important, so D might be a reason as well, but I need to double-check that.

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Tijuana

3 months ago

I practiced a question like this, and I feel like mismatched router IDs could be a factor, but I can't recall if that's specifically for L2 routers.

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Major

4 months ago

I'm not entirely sure, but I think if the ISO address isn't configured, that could definitely prevent adjacency. So, B might be right too.

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Aimee

4 months ago

I remember something about mismatched area IDs causing adjacency issues, so maybe option C is a good choice.

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Miriam

4 months ago

This seems straightforward. The key is to identify any mismatches in the router ID or area ID between the two routers. That's probably the issue here.

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Twana

4 months ago

I'm a bit confused on this one. I know it's related to the IS-IS configuration, but I'm not sure which specific settings could be causing the problem.

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