mediumMultiple Choice
300-410 Practice Question: Is troubleshooting a routing issue in an EIGRP…
A network engineer is troubleshooting a routing issue in an EIGRP network. Router R1 is not learning a specific route from its neighbor R2, even though R2 has the route in its routing table. The engineer checks the EIGRP topology table on R1 and does not see the route. The output of 'show ip eigrp neighbors' shows that R1 and R2 are adjacent. What should the engineer check next?
⚠ Common exam trap
Cisco often tests the distinction between a route being absent from the topology table versus being present but not selected as the best path; candidates may incorrectly assume metric issues or summarization when the real cause is a distribute-list filtering the route before it enters the topology table.
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
✓
Check if a distribute-list in or out is applied under the EIGRP process on R1.
If R1 and R2 are EIGRP neighbors but R1 does not have the route in its topology table, a distribute-list applied inbound on R1 or outbound on R2 could be filtering the route. Distribute-lists use access-lists or prefix-lists to permit or deny routes during the update process, preventing specific routes from being installed in the topology table even though the neighbor adjacency is established.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Check if a distribute-list in or out is applied under the EIGRP process on R1.
Why this is correct
A distribute-list applied inbound or outbound filters routes before they enter the topology table, so R1 can remain adjacent to R2 yet never install the prefix. Checking the EIGRP process for such an access-list directly addresses the missing route.
- ✗
Check if the route is being summarized on R2.
Why it's wrong here
Summarisation on R2 would hide the specific prefix, but the stem says R2 holds the route and R1 sees no topology entry at all, which points to a filtering or distribute-list issue rather than aggregation. Summarisation is the right check when R1 receives a covering summary instead of the exact prefix.
- ✗
Check if the EIGRP metric for the route is too high.
Why it's wrong here
An excessively high metric would still install the route in the topology table as a feasible successor candidate; it would only affect best-path selection. The stem shows no topology entry whatsoever, so the route is being suppressed before metric comparison, for example by a distribute list or prefix filter.
- ✗
Check if the route is a connected route on R2.
Why it's wrong here
A connected route on R2 is still redistributed or advertised into EIGRP if configured, so its origin does not by itself prevent R1 from receiving it. This check is tempting when verifying redistribution, but the missing topology entry on R1 indicates filtering or summarisation, not the route's source type.
Visual reference
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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