- A
The route 10.1.1.0/24 has become unreachable, and EIGRP is querying neighbors.
Why wrong: The route is still reachable with a new successor; no query is sent because a feasible successor exists.
- B
EIGRP is performing a Diffusing Update Algorithm (DUAL) recomputation due to a metric increase, but a feasible successor is available, so no query is needed.
The metric increased, but a feasible successor was found, allowing immediate convergence without queries.
- C
The route is being removed from the topology table because the metric changed.
Why wrong: The route remains in the topology table with a new successor.
- D
EIGRP is sending a query to all neighbors because no feasible successor exists.
Why wrong: The debug shows a feasible successor was found, so no query is sent.
300-410 EIGRP Troubleshooting Practice Question
This 300-410 practice question tests your understanding of eigrp troubleshooting. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A network engineer runs the following command to troubleshoot an EIGRP issue:
R1# debug eigrp fsm *Mar 1 00:20:45.678: EIGRP: 10.1.1.0/24 - do advertising, metric 131072 *Mar 1 00:20:45.678: EIGRP: 10.1.1.0/24 - route installed in table *Mar 1 00:20:45.678: EIGRP: 10.1.1.0/24 - metric change from 131072 to 131328 *Mar 1 00:20:45.678: EIGRP: 10.1.1.0/24 - find FS, metric 131328, RD 130816 *Mar 1 00:20:45.678: EIGRP: 10.1.1.0/24 - found FS via 10.1.3.3, metric 131328 *Mar 1 00:20:45.678: EIGRP: 10.1.1.0/24 - new successor is 10.1.3.3
What does this output indicate?
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
EIGRP is performing a Diffusing Update Algorithm (DUAL) recomputation due to a metric increase, but a feasible successor is available, so no query is needed.
The debug output shows EIGRP detecting a metric change for 10.1.1.0/24 from 131072 to 131328. DUAL then searches for a feasible successor (FS) and finds one via 10.1.3.3 with a reported distance (RD) of 130816, which is less than the current feasible distance (FD) of 131072. Because a feasible successor exists, DUAL installs the new route without sending queries, confirming option B.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 route 10.1.1.0/24 has become unreachable, and EIGRP is querying neighbors.
Why it's wrong here
The route is still reachable with a new successor; no query is sent because a feasible successor exists.
- ✓
EIGRP is performing a Diffusing Update Algorithm (DUAL) recomputation due to a metric increase, but a feasible successor is available, so no query is needed.
Why this is correct
The metric increased, but a feasible successor was found, allowing immediate convergence without queries.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The route is being removed from the topology table because the metric changed.
Why it's wrong here
The route remains in the topology table with a new successor.
- ✗
EIGRP is sending a query to all neighbors because no feasible successor exists.
Why it's wrong here
The debug shows a feasible successor was found, so no query is sent.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between a local DUAL computation (when a feasible successor exists) and an active query process (when no feasible successor exists), and the trap here is assuming any metric change triggers queries or route removal.
Trap categories for this question
Command / output trap
The debug shows a feasible successor was found, so no query is sent.
Detailed technical explanation
How to think about this question
The Diffusing Update Algorithm (DUAL) uses the feasible distance (FD) and reported distance (RD) to determine if a neighbor is a feasible successor. The feasibility condition requires RD < FD; here, RD 130816 is less than the original FD 131072, allowing a local update without queries. In real-world scenarios, this prevents network-wide convergence delays when a link metric increases but an alternate path still satisfies the condition.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
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.
What to study next
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FAQ
Questions learners often ask
What does this 300-410 question test?
EIGRP Troubleshooting — This question tests EIGRP Troubleshooting — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: EIGRP is performing a Diffusing Update Algorithm (DUAL) recomputation due to a metric increase, but a feasible successor is available, so no query is needed. — The debug output shows EIGRP detecting a metric change for 10.1.1.0/24 from 131072 to 131328. DUAL then searches for a feasible successor (FS) and finds one via 10.1.3.3 with a reported distance (RD) of 130816, which is less than the current feasible distance (FD) of 131072. Because a feasible successor exists, DUAL installs the new route without sending queries, confirming option B.
What should I do if I get this 300-410 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
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