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300-410 Practice Question: Runs the following command to troubleshoot an…
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?
⚠ Common exam trap
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.
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.
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.
- ✗
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.
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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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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