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300-410 Practice Question: Is troubleshooting an EIGRP adjacency that is not…
A network engineer is troubleshooting an EIGRP adjacency that is not forming. Both routers are configured for EIGRP with BFD. The engineer checks the BFD session and sees it is 'Down'. The interface between the routers is up/up. The EIGRP configuration appears correct. What is the most likely cause?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The BFD timers are configured with 'bfd interval 50 min_rx 50 multiplier 3' on one router and 'bfd interval 100 min_rx 100 multiplier 3' on the other, causing a negotiation failure.
EIGRP BFD requires that the BFD session be established before the EIGRP adjacency can form. If the BFD session is down, the issue is often a mismatch in BFD parameters or a lack of BFD configuration on one side.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The EIGRP process is configured with 'bfd all-interfaces' but the interface is not configured with 'eigrp bfd'.
Why it's wrong here
The 'bfd all-interfaces' command under EIGRP enables BFD on all interfaces that have EIGRP enabled, so this would not cause the issue.
- ✓
The BFD timers are configured with 'bfd interval 50 min_rx 50 multiplier 3' on one router and 'bfd interval 100 min_rx 100 multiplier 3' on the other, causing a negotiation failure.
Why this is correct
BFD timers must be compatible; if the required interval or multiplier values are not negotiable, the session will fail to come up.
- ✗
The interface is configured with 'ip address 10.0.0.1 255.255.255.252' but the neighbor is using a different subnet.
Why it's wrong here
A subnet mismatch would prevent EIGRP from forming, but BFD would still attempt to form; the BFD session would show 'Down' due to no response.
- ✗
The EIGRP autonomous system number is mismatched between the two routers.
Why it's wrong here
AS number mismatch would prevent EIGRP adjacency, but BFD would still attempt to form; the BFD session would show 'Down' due to no response.
Quick reference
Routing Protocol Comparison
| Protocol | Metric | Max Hops | Algorithm | Type |
|---|---|---|---|---|
| RIP v2 | Hop count | 15 | Bellman-Ford | Distance vector |
| OSPF | Cost (bandwidth) | Unlimited | Dijkstra (SPF) | Link state |
| EIGRP | Composite metric | Unlimited | DUAL | Hybrid |
| IS-IS | Cost | Unlimited | Dijkstra | Link state |
| BGP | Policy / attributes | Unlimited | Path vector | Path vector |
RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 300-410 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 300-410 exam.