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Juniper JN0-351 Exam - Topic 6 Question 51 Discussion

You are configuring an IS-IS IGP network and do not see the IS-IS adjacencies established. In this scenario, what are two reasons for this problem? (Choose two.)
A) MTU is not at least 1492 bytes. and D) The lo0 interface is not included as an IS-IS interface.
B) IP subnets are not a /30 address.
C) The Level 2 routers have mismatched areas.

Juniper JN0-351 Exam - Topic 6 Question 51 Discussion

Actual exam question for Juniper's JN0-351 exam
Question #: 51
Topic #: 6
[All JN0-351 Questions]

You are configuring an IS-IS IGP network and do not see the IS-IS adjacencies established. In this scenario, what are two reasons for this problem? (Choose two.)

Show Suggested Answer Hide Answer
Suggested Answer: A, D

Option A suggests that the MTU is not at least 1492 bytes.This is correct because IS-IS requires a minimum MTU of 1492 bytes to establish adjacencies1.If the MTU is less than this, IS-IS adjacencies will not be established1.

Option D suggests that the lo0 interface is not included as an IS-IS interface.This is also correct because the loopback interface (lo0) is typically used as the router ID in IS-IS1.If the loopback interface is not included in IS-IS, it could prevent IS-IS adjacencies from being established1.

Therefore, options A and D are correct.


by Sheridan at Jan 05, 2026, 05:16 AM

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Ronald
2 months ago
I feel like B isn’t relevant here. The /30 subnet isn’t a requirement for IS-IS.
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Dick
2 months ago
I’m leaning towards A and D. If lo0 isn’t included, that could stop adjacencies too.
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Felicidad
3 months ago
I agree, A is definitely a factor. But C makes sense too, mismatched areas can prevent adjacencies.
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Matthew
3 months ago
I think A and C are likely reasons. MTU issues can really mess things up.
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Stephaine
3 months ago
Totally agree with C), mismatched areas are a big deal!
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Yuonne
3 months ago
B) subnets being /30 isn't a requirement for IS-IS, right?
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Marshall
3 months ago
Wait, does the lo0 interface really need to be included?
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Linwood
3 months ago
I think C) is a common mistake too!
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Marquetta
4 months ago
A) MTU issues can definitely cause adjacency problems.
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Matthew
4 months ago
Ah, the good old IS-IS adjacency problems. Brings back memories of my CCIE lab days. A and C are spot on.
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Ressie
4 months ago
The /30 subnet thing is just silly. Who uses that for an IGP these days? A and C are the way to go.
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Lucina
5 months ago
Haha, I bet the person who wrote this question was an OSPF fan trying to trick us. IS-IS is way cooler than that old protocol.
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Marylin
5 months ago
I agree, A and C are the right choices. Mismatched areas can definitely cause issues with IS-IS adjacencies.
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Denise
5 months ago
The correct answers are A and C. MTU needs to be at least 1492 bytes, and the Level 2 routers must have the same area.
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Cheryl
5 months ago
I thought the /30 subnet was more relevant for point-to-point links, but I’m not convinced it’s a reason for adjacencies not forming.
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Izetta
5 months ago
I practiced a question like this, and I feel like the loopback interface not being included could also be a factor, so D might be worth considering.
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Carolynn
5 months ago
I’m not entirely sure, but I think mismatched areas could definitely cause issues, so maybe C is correct too.
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Rusty
6 months ago
I remember something about MTU settings being crucial for adjacencies, so A might be a good choice.
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Allene
6 months ago
Ugh, IS-IS adjacencies can be tricky. I'm going to have to really think through the key configuration requirements here. The areas and loopback interface are good places to start troubleshooting.
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Katie
6 months ago
I feel pretty confident about this one. The mismatched areas and missing loopback interface are the two most likely culprits here. The subnet size and MTU are good to verify, but those aren't the main problems.
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Pete
6 months ago
Okay, let's see. I'm pretty sure the mismatched areas would definitely cause an issue with the adjacency. And I think the loopback interface needs to be included as well. The subnet size and MTU are good things to double-check too.
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Gerald
6 months ago
Hmm, this one has me a bit stumped. I know the IS-IS adjacency has some specific configuration needs, but I'm not remembering all the details off the top of my head.
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Hubert
7 months ago
I think the key here is to focus on the IS-IS adjacency requirements. The MTU and subnet size seem like they could be factors, but I'm not totally sure.
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Christoper
11 days ago
Don't forget about the lo0 interface. It needs to be included!
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Serita
16 days ago
Definitely! A mismatch can break connections.
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Zack
2 months ago
MTU settings are crucial for adjacencies.
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