- A
Verify routing entries on both routers to ensure the remote internal subnets are reachable via the tunnel.
Both routers need to have routes pointing to the remote internal subnets (e.g., 192.168.1.0/24 and 10.0.1.0/24) with the tunnel interface as the next hop. Without these routes, traffic from internal hosts will not be directed into the tunnel.
- B
Check the IPsec security associations for encryption algorithm mismatch.
Why wrong: If the tunnel is active and both sides can ping tunnel IPs, the IPsec parameters are correctly negotiated. An algorithm mismatch would prevent the tunnel from establishing.
- C
Disable the firewall on the internal interfaces temporarily.
Why wrong: The firewall rules already permit traffic. Disabling firewalls is not a best practice and would not resolve a routing issue.
- D
Regenerate the pre-shared key on both sides.
Why wrong: Regenerating the PSK is unnecessary because the tunnel is already established. The PSK is only used during initial authentication.
Quick Answer
The correct next step is to verify routing entries on both routers to ensure the remote internal subnets are reachable via the tunnel. This is because an active IPsec VPN with successful pings to the tunnel interfaces confirms that encryption and decryption are working, but traffic to the actual internal hosts (like 10.0.1.10 or 192.168.1.10) still needs a route that points to the tunnel interface. Without those specific routes, packets destined for the remote LAN will be forwarded out the default gateway or dropped, even though the tunnel is up. On the CompTIA Network+ N10-009 exam, this scenario tests your ability to distinguish between a functional tunnel and proper routing—a common trap is assuming a working tunnel means all traffic flows correctly. Remember the memory tip: “Tunnel up, route down—check the table before you frown.”
N10-009 Network Implementation Practice Question
This N10-009 practice question tests your understanding of network implementation. 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 has successfully established an IPsec site-to-site VPN tunnel between a branch office (10.0.1.0/24) and the main office (192.168.1.0/24). The tunnel status shows as active, and both sides can ping each other's tunnel interface IP addresses. However, users at the branch office cannot ping the main office server at 192.168.1.10, and the main office cannot ping the branch office server at 10.0.1.10. The firewall rules on both sides permit IPsec traffic and all internal traffic. What should the engineer check NEXT?
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
Verify routing entries on both routers to ensure the remote internal subnets are reachable via the tunnel.
The tunnel is active and both sides can ping each other's tunnel interface IPs, confirming that IPsec phase 1 and phase 2 are established and the tunnel itself is functional. However, users cannot reach the remote internal subnets (10.0.1.0/24 and 192.168.1.0/24), which indicates a routing problem: the routers likely lack routes for those remote subnets pointing to the tunnel interface. Without proper routing entries, traffic destined for the remote LAN is sent out the wrong interface or dropped, even though the tunnel is up.
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.
- ✓
Verify routing entries on both routers to ensure the remote internal subnets are reachable via the tunnel.
Why this is correct
Both routers need to have routes pointing to the remote internal subnets (e.g., 192.168.1.0/24 and 10.0.1.0/24) with the tunnel interface as the next hop. Without these routes, traffic from internal hosts will not be directed into the tunnel.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Check the IPsec security associations for encryption algorithm mismatch.
- ✗
Disable the firewall on the internal interfaces temporarily.
Why it's wrong here
The firewall rules already permit traffic. Disabling firewalls is not a best practice and would not resolve a routing issue.
- ✗
Regenerate the pre-shared key on both sides.
Why it's wrong here
Regenerating the PSK is unnecessary because the tunnel is already established. The PSK is only used during initial authentication.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between tunnel reachability (pinging the tunnel interface IP) and subnet reachability (pinging hosts behind the tunnel), trapping candidates who assume a working tunnel automatically means all traffic flows correctly, when in fact routing for the remote LANs must be explicitly configured.
Detailed technical explanation
How to think about this question
In IPsec site-to-site VPNs, the tunnel interface (e.g., a virtual tunnel interface or crypto map) provides a logical path, but the router must have a route for the remote subnet pointing to that tunnel interface (e.g., 'ip route 192.168.1.0 255.255.255.0 Tunnel0'). Without this route, traffic to the remote LAN is forwarded based on the default routing table, often out the physical WAN interface, bypassing the encryption and failing to reach the destination. A common verification command is 'show ip route' to confirm the presence of these static or dynamic routes.
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.
What to study next
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FAQ
Questions learners often ask
What does this N10-009 question test?
Network Implementation — This question tests Network Implementation — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Verify routing entries on both routers to ensure the remote internal subnets are reachable via the tunnel. — The tunnel is active and both sides can ping each other's tunnel interface IPs, confirming that IPsec phase 1 and phase 2 are established and the tunnel itself is functional. However, users cannot reach the remote internal subnets (10.0.1.0/24 and 192.168.1.0/24), which indicates a routing problem: the routers likely lack routes for those remote subnets pointing to the tunnel interface. Without proper routing entries, traffic destined for the remote LAN is sent out the wrong interface or dropped, even though the tunnel is up.
What should I do if I get this N10-009 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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Last reviewed: Jun 11, 2026
This N10-009 practice question is part of Courseiva's free CompTIA 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 N10-009 exam.
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