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300-410 Practice Question: An EIGRP network with routers R1, R2, and R3 is…
An EIGRP network with routers R1, R2, and R3 is experiencing frequent Stuck-in-Active (SIA) events for the prefix 172.16.1.0/24. R1 is the successor, R2 is the feasible successor. R3 is a query originator. 'show ip eigrp topology 172.16.1.0/24' on R1 shows the route in active state. 'show ip eigrp interfaces' on R2 shows the link to R3 is up but with high packet loss. What is the root cause?
⚠ Common exam trap
Cisco often tests the misconception that SIA is always caused by a slow or congested link directly between the query originator and the successor, but here the trap is that the packet loss is on the link between R2 and R3, which indirectly prevents R2 from replying to R1, causing SIA.
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
✓
High packet loss on the link between R2 and R3 causes EIGRP queries or replies to be dropped, leading to SIA.
The high packet loss on the link between R2 and R3 causes EIGRP queries or replies to be dropped. When R3 originates a query for the prefix 172.16.1.0/24, R1 (the successor) transitions the route to active state and sends queries to all neighbors, including R2. R2, as the feasible successor, must reply, but if the link to R3 has high packet loss, the query from R2 to R3 or the reply from R3 back to R2 may be lost, preventing R2 from sending its reply to R1 within the active timer, leading to a Stuck-in-Active (SIA) event.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
High packet loss on the link between R2 and R3 causes EIGRP queries or replies to be dropped, leading to SIA.
Why this is correct
EIGRP relies on reliable transport; packet loss can cause queries to remain unanswered, triggering SIA after the active timer expires.
- ✗
R3 has a route summarization that causes the query to be sent to the Null0 interface.
Why it's wrong here
Summarization could cause issues, but the SIA is due to lost packets, not summarization.
- ✗
The EIGRP active timer is set too low on R1, causing premature SIA.
Why it's wrong here
The active timer default is 3 minutes; packet loss is a more likely cause than timer misconfiguration.
- ✗
R2 has a distribute-list that filters the prefix, preventing the reply from being sent.
Why it's wrong here
If a distribute-list blocked the prefix, the route would not be in the topology table; SIA occurs when a query is sent but no reply is received.
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 by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 300-410 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 300-410 exam.