300-410 Layer 3 Technologies Practice Question
A network administrator is troubleshooting an EIGRP network where a router is not receiving all expected routes from a neighbor. The neighbor relationship is established, and the topology table shows only a subset of routes. Which EIGRP feature could be filtering the routes?
⚠ Common exam trap
Test-takers frequently confuse route filtering with neighbor adjacency issues; a distribute-list can silently drop routes without affecting the neighbor relationship.
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 route filtering using distribute-list
EIGRP distribute-lists can filter routes either inbound or outbound. An inbound distribute-list applied on the local router can prevent specific routes from entering the topology table, even though the neighbor adjacency is up. This is a common cause of missing routes when the neighbor relationship is healthy. The distribute-list can use ACLs, prefix-lists, or route-maps to match and filter routes.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
EIGRP route filtering using distribute-list
Why this is correct
A distribute-list can filter incoming or outgoing EIGRP routes. If applied inbound on the local router, it can prevent specific routes from being installed in the topology table. This matches the symptom of missing routes despite an established neighbor relationship. The distribute-list can reference an ACL or prefix-list to selectively filter routes based on network numbers or masks.
- ✗
EIGRP variance
Why it's wrong here
EIGRP variance allows unequal-cost load balancing by multiplying the feasible distance. It does not filter routes from the topology table; it only affects which routes are installed in the routing table. Missing routes in the topology table cannot be caused by variance, as variance operates on routes already present in the topology table.
- ✗
EIGRP authentication mismatch
Why it's wrong here
An authentication mismatch would prevent the neighbor relationship from forming altogether, resulting in no routes being received. In this scenario, the neighbor relationship is established, so authentication is not the issue. Authentication problems typically cause neighbor adjacency failures, not partial route reception.
- ✗
EIGRP stub routing
Why it's wrong here
EIGRP stub routing restricts the router to advertise only a summary or specific routes to its neighbors, but it does not filter incoming routes. The scenario describes a router not receiving routes from a neighbor, so stub routing on the local router would not cause this. Stub routing would affect what the local router advertises, not what it receives.
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 and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
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