N10-009 Network Troubleshooting 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.

• ✓

  Server A's firewall is blocking incoming ICMP

  Why this is correct

  If Server A's firewall is configured to block incoming ICMP echo requests (ping), Server B's ping attempts to Server A will time out. However, if Server A initiates a ping to Server B, the firewall typically permits the outgoing ICMP echo request and allows the corresponding incoming ICMP echo reply, demonstrating full connectivity from Server A's perspective. This creates the observed one-way communication failure where Server B cannot reach Server A via ping, but Server A can reach Server B.

• ✗

  Server B's firewall is blocking outgoing ICMP

  Why it's wrong here

  If Server B's firewall blocked outgoing ICMP, it would not send the ping request, and Server A would not receive the ping attempt. The symptom would be 'destination unreachable' from Server B, but Server A would see no request. However, Server A can ping Server B, so Server B replies are allowed in. Blocking only outgoing requests on Server B would result in a different failure (Server B cannot initiate pings, but could still receive them). Given the symptom, blocking incoming on Server A is more common.

  When this WOULD be correct

  In a scenario where Server A cannot ping Server B by IP, but Server B can ping Server A, and both are in the same VLAN/subnet with no ACLs, Server B's firewall blocking outgoing ICMP would explain why A's pings fail while B's succeed.

• ✗

  The cable connecting Server A is faulty

  Why it's wrong here

  A faulty network cable, whether due to a broken wire, poor termination, or excessive length, would typically disrupt the physical layer connectivity for Server A. Such an issue would manifest as intermittent packet loss, complete link failure, or very high error rates, affecting communication in *both* directions. It would not selectively block only incoming ICMP echo requests while allowing outgoing ICMP traffic and its corresponding replies, which is the specific symptom described.

  When this WOULD be correct

  In a scenario where both servers cannot communicate in either direction (e.g., no pings succeed), and physical inspection shows damage or link lights are off, a faulty cable on one server would be the likely cause.

• ✗

  There is a duplex mismatch on Server B's switch port

  Why it's wrong here

  A duplex mismatch occurs when one device operates in full-duplex mode while the other operates in half-duplex mode. This scenario leads to severe network performance degradation, characterized by high collision rates, late collisions, and significant frame errors on the half-duplex side, and potentially excessive retransmissions on the full-duplex side. While it severely impacts communication, it typically results in poor performance or intermittent connectivity in *both* directions, not a complete, consistent one-way failure of a specific protocol like ICMP.

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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