- A
The EIGRP hello packets are being encrypted but the reply is not, causing asymmetric routing.
Why wrong: Asymmetric routing would not cause SIA; EIGRP uses reliable transport for queries and replies, and unidirectional packet loss is the key issue.
- B
The IPsec ACL is permitting EIGRP packets (protocol 88) only in one direction, so queries are sent but replies are dropped by the remote router's crypto map.
If the crypto ACL on one router permits only certain traffic (e.g., TCP/179 for BGP) but not EIGRP, EIGRP packets may be dropped. If the other router's ACL permits EIGRP, the neighbor forms partially, but queries may not be replied to, causing SIA.
- C
The EIGRP K-values are mismatched between the two routers.
Why wrong: Mismatched K-values prevent neighbor formation entirely, not causing SIA.
- D
The IPsec tunnel is using aggressive mode, which does not support multicast traffic.
Why wrong: Aggressive mode affects IKE phase 1, not the encapsulation of multicast traffic; EIGRP uses multicast 224.0.0.10, which is supported in tunnel mode.
300-410 IPsec Site-to-Site VPN Practice Question
This 300-410 practice question tests your understanding of ipsec site-to-site vpn. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 engineer configures an IPsec site-to-site VPN between two routers running EIGRP. The EIGRP neighbor forms, but routes are not being exchanged. The engineer notices that the EIGRP neighbor is stuck in active state for certain routes. What is the most likely explanation?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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 IPsec ACL is permitting EIGRP packets (protocol 88) only in one direction, so queries are sent but replies are dropped by the remote router's crypto map.
When EIGRP neighbors form but routes are not exchanged and the neighbor is stuck in active (SIA) state, it indicates that EIGRP queries are being sent but replies are not received. In an IPsec VPN, if the crypto ACL permits EIGRP (protocol 88) only in one direction, queries from one router are encrypted and sent, but the remote router's crypto map does not match the reply packets, so they are dropped. This prevents the EIGRP query/reply process from completing, causing routes to remain in active state and not be exchanged.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 EIGRP hello packets are being encrypted but the reply is not, causing asymmetric routing.
Why it's wrong here
Asymmetric routing would not cause SIA; EIGRP uses reliable transport for queries and replies, and unidirectional packet loss is the key issue.
- ✓
The IPsec ACL is permitting EIGRP packets (protocol 88) only in one direction, so queries are sent but replies are dropped by the remote router's crypto map.
Why this is correct
If the crypto ACL on one router permits only certain traffic (e.g., TCP/179 for BGP) but not EIGRP, EIGRP packets may be dropped. If the other router's ACL permits EIGRP, the neighbor forms partially, but queries may not be replied to, causing SIA.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The EIGRP K-values are mismatched between the two routers.
Why it's wrong here
Mismatched K-values prevent neighbor formation entirely, not causing SIA.
- ✗
The IPsec tunnel is using aggressive mode, which does not support multicast traffic.
Why it's wrong here
Aggressive mode affects IKE phase 1, not the encapsulation of multicast traffic; EIGRP uses multicast 224.0.0.10, which is supported in tunnel mode.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that EIGRP neighbor formation implies full route exchange, but the trap here is that a one-way crypto ACL permits neighbor formation (since hellos are multicast and may be permitted) but blocks query/reply unicast traffic, causing SIA routes.
Detailed technical explanation
How to think about this question
EIGRP uses reliable multicast for queries and unicast for replies; if the crypto ACL is misconfigured to only permit EIGRP in one direction (e.g., only from source to destination), the reply packets (unicast, protocol 88) are not encrypted and are dropped by the remote router's crypto map because they do not match the permit statement. This leads to the SIA condition as the querying router never receives a reply, and the route remains in active state until the active timer expires (typically 3 minutes).
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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FAQ
Questions learners often ask
What does this 300-410 question test?
IPsec Site-to-Site VPN — This question tests IPsec Site-to-Site VPN — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The IPsec ACL is permitting EIGRP packets (protocol 88) only in one direction, so queries are sent but replies are dropped by the remote router's crypto map. — When EIGRP neighbors form but routes are not exchanged and the neighbor is stuck in active (SIA) state, it indicates that EIGRP queries are being sent but replies are not received. In an IPsec VPN, if the crypto ACL permits EIGRP (protocol 88) only in one direction, queries from one router are encrypted and sent, but the remote router's crypto map does not match the reply packets, so they are dropped. This prevents the EIGRP query/reply process from completing, causing routes to remain in active state and not be exchanged.
What should I do if I get this 300-410 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
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.
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