This 300-410 practice question tests your understanding of ipsec site-to-site vpn. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
A network engineer runs the following command to troubleshoot an IPsec Site-to-Site VPN issue:
R1# show crypto engine connections active
Crypto Engine Connections
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The IPsec SAs are established but no traffic is flowing, possibly due to routing or ACL issues.
The output shows three IPsec Security Associations (SAs) with zero encrypted and zero decrypted packets, and a LastSeqNo of 0. This indicates the SAs are established (the tunnels are up) but no traffic is being processed through them. The most common causes are routing issues preventing traffic from reaching the tunnel interface, or ACLs that do not match the interesting traffic for encryption.
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 IPsec VPN is actively encrypting and decrypting traffic.
Why it's wrong here
All counters are zero, indicating no traffic.
✓
The IPsec SAs are established but no traffic is flowing, possibly due to routing or ACL issues.
Why this is correct
Zero packets suggest the SAs are idle; the issue is likely with traffic matching the crypto ACL or routing.
Related concept
Read the scenario before looking for a memorised answer.
✗
The crypto engine is overloaded and cannot process packets.
Why it's wrong here
There is no indication of overload; the connections are simply idle.
✗
The IPsec SAs are using the wrong transform set.
Why it's wrong here
The transform sets are shown, but the issue is lack of traffic, not transform mismatch.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that a non-zero number of SAs in 'show crypto engine connections active' automatically means traffic is flowing, when in fact the Encrypt/Decrypt counters must be checked to confirm actual data processing.
Trap categories for this question
Command / output trap
The transform sets are shown, but the issue is lack of traffic, not transform mismatch.
Detailed technical explanation
How to think about this question
The 'show crypto engine connections active' command displays active IPsec SAs and their packet counters. A LastSeqNo of 0 confirms no packets have been processed, which often points to a missing or incorrect crypto map ACL that defines interesting traffic, or a routing issue where traffic is not being forwarded to the tunnel interface. In real-world scenarios, this is a common troubleshooting step after verifying that IKE Phase 1 and Phase 2 are complete (e.g., via 'show crypto isakmp sa' and 'show crypto ipsec sa').
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 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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
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 SAs are established but no traffic is flowing, possibly due to routing or ACL issues. — The output shows three IPsec Security Associations (SAs) with zero encrypted and zero decrypted packets, and a LastSeqNo of 0. This indicates the SAs are established (the tunnels are up) but no traffic is being processed through them. The most common causes are routing issues preventing traffic from reaching the tunnel interface, or ACLs that do not match the interesting traffic for encryption.
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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