N10-009 Network Implementation Practice Question

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.

• ✗

  Check the IPsec security associations for encryption algorithm mismatch.

  Why it's wrong here

  An encryption algorithm mismatch, or any other mismatch in IPsec Security Association (SA) parameters (like hashing algorithms or Diffie-Hellman groups), would prevent the IPSec tunnel from successfully establishing in the first place. Since the question states the tunnel has been "successfully established," it confirms that all IKE Phase 1 and Phase 2 parameters, including encryption algorithms, have been correctly negotiated and agreed upon by both VPN peers. Therefore, checking for such a mismatch is irrelevant to a problem where the tunnel is up but traffic isn't flowing.

  When this WOULD be correct

  In a scenario where the IPsec tunnel status shows as active but pings between tunnel interfaces fail, or the tunnel fails to establish, checking for encryption algorithm mismatch would be the next step.

• ✗

  Disable the firewall on the internal interfaces temporarily.

  Why it's wrong here

  Disabling firewalls on internal interfaces is a significant security risk and an inappropriate troubleshooting step when the VPN tunnel itself is established. If the tunnel is up, it implies that necessary firewall rules for IPSec (e.g., UDP 500, UDP 4500, ESP protocol 50, AH protocol 51) are already permitting the control plane traffic. The issue described, where the tunnel is up but traffic isn't flowing, points to a routing problem, not a firewall blocking *internal* traffic that should be encapsulated by the VPN.

  When this WOULD be correct

  In a scenario where the IPsec tunnel is up, pings to tunnel interfaces succeed, but internal traffic fails, and the firewall logs show dropped packets for internal traffic. The engineer has verified routing and IPsec SAs, and suspects a firewall rule blocking internal traffic between the subnets. Temporarily disabling the firewall would isolate the issue.

• ✗

  Regenerate the pre-shared key on both sides.

  Why it's wrong here

  If the IPSec site-to-site VPN tunnel has been successfully established, it means the pre-shared key (PSK) was correctly configured and used during the Internet Key Exchange (IKE) Phase 1 for mutual authentication. Regenerating the PSK would disrupt the active tunnel and require re-authentication, which is counterproductive when the problem lies elsewhere, specifically with traffic not traversing the *established* tunnel. The PSK's role is solely for initial peer authentication, not for ongoing data plane issues after tunnel establishment.

  When this WOULD be correct

  If the tunnel status showed as down or the ping to the tunnel interface IPs failed, and logs indicated authentication failures, then regenerating the pre-shared key on both sides would be the next step to resolve a key mismatch.

Option-by-option analysis

Why each answer is right or wrong

Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The N10-009 exam frequently reuses these exact scenarios with slightly different constraints.

Analysis generated from the official N10-009blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”

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