- A
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.
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.
- B
The EIGRP K-values are mismatched between R1 and R2.
Why wrong: K-value mismatch would prevent adjacency formation, but the adjacency is up (since queries are sent).
- C
The route 192.168.1.0/24 is not in R1's topology table, so it cannot reply.
Why wrong: Even if the route is not in the topology table, R1 should reply with an unreachable message. The distribute-list blocks the query entirely.
- D
The EIGRP timers on R1 are set too high, causing a delay in reply.
Why wrong: Timer mismatch would not cause SIA if replies are sent; the issue is that no reply is sent at all.
300-410 Route Maps and Route Filtering Practice Question
This 300-410 practice question tests your understanding of route maps and route filtering. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
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?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"never"Why it matters: Absolute qualifier. True only if the statement has zero exceptions — be cautious of options that seem obvious but break down in edge cases.
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.
Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
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.
Clue confirmation
The clue word "never" in the question point toward this answer.
Related concept
Standard ACLs match source addresses.
- ✗
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.
Common exam traps
Common exam trap: ACLs stop at the first match
ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.
Detailed technical explanation
How to think about this question
ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.
KKey Concepts to Remember
- Standard ACLs match source addresses.
- Extended ACLs can match source, destination, protocol and ports.
- The first matching ACL entry is used.
- There is usually an implicit deny at the end.
TExam Day Tips
- Check inbound versus outbound direction.
- Read the ACL from top to bottom.
- Look for a broader permit or deny above the intended line.
Key takeaway
ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Real-world example
How this comes up in practice
A security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
What to study next
Got this wrong? Here's your next step.
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related 300-410 ACL questions on filtering logic and placement.
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FAQ
Questions learners often ask
What does this 300-410 question test?
Route Maps and Route Filtering — This question tests Route Maps and Route Filtering — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: 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.
What should I do if I get this 300-410 question wrong?
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related 300-410 ACL questions on filtering logic and placement.
Are there clue words in this question I should notice?
Yes — watch for: "never". Absolute qualifier. True only if the statement has zero exceptions — be cautious of options that seem obvious but break down in edge cases.
What is the key concept behind this question?
Standard ACLs match source addresses.
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Last reviewed: Jun 18, 2026
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