hardMultiple ChoiceObjective-mapped
300-410 Practice Question: An EIGRP network is experiencing a…
An EIGRP network is experiencing a stuck-in-active (SIA) condition for a route 192.168.1.0/24. R1 has the following configuration: router eigrp 100 network 10.0.0.0 distribute-list prefix PL-FILTER in. R2 shows: 'show ip eigrp topology 192.168.1.0/24' is in active state, and 'show ip eigrp events' shows that R1 sent a query but never received a reply. R1's prefix-list PL-FILTER permits only 10.0.0.0/8. What is the root 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 distribute-list inbound on R1 filters the EIGRP query for 192.168.1.0/24, preventing R1 from replying and causing SIA on R2.
The distribute-list prefix PL-FILTER in on R1 filters incoming routes, but it also affects queries. When R2 sends a query for 192.168.1.0/24, R1 receives it but the distribute-list filters the query (since the prefix is not permitted), so R1 does not process it and does not send a reply. This causes R2 to wait indefinitely for a reply, leading to an SIA condition. The distribute-list should be applied outbound or should permit the necessary prefixes to allow queries to be processed.
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 distribute-list inbound on R1 filters the EIGRP query for 192.168.1.0/24, preventing R1 from replying and causing SIA on R2.
Why this is correct
EIGRP distribute-lists applied inbound also filter queries. Since the prefix 192.168.1.0/24 is not permitted by PL-FILTER, R1 drops the query and does not send a reply, leaving R2 in active state.
- ✗
The EIGRP K-values are mismatched between R1 and R2.
Why it's wrong here
K-value mismatch would prevent adjacency formation, but the adjacency is up (since queries are sent).
- ✗
The route 192.168.1.0/24 is not in R1's topology table, so it cannot reply.
Why it's wrong here
Even if the route is not in the topology table, R1 should reply with an unreachable message. The distribute-list blocks the query entirely.
- ✗
The EIGRP timers on R1 are set too high, causing a delay in reply.
Why it's wrong here
Timer mismatch would not cause SIA if replies are sent; the issue is that no reply is sent at all.
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.
Go deeper
Related to this question
Learn chapter
Introduction to ENARSI Exam and Network Fundamentals
Key term
ACL for Routing Protocols
An ACL for Routing Protocols is a set of rules used to filter routing updates between routers, controlling which network routes are advertised or accepted to improve security and stability.
Key term
BGP Prefix Filtering
BGP Prefix Filtering is the practice of controlling which network routes (prefixes) a router accepts or advertises to its BGP neighbors, preventing unwanted or harmful routes from spreading across the internet.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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