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.

• ✗

  VLAN 30 is not allowed on the trunk port to the switch.

  Why it's wrong here

  Trunk ports are primarily used to carry traffic for multiple VLANs across inter-switch links, allowing VLANs to span multiple physical switches. In a scenario where all VLANs (VLAN 10, VLAN 20, VLAN 30) are configured on a single Layer 3 switch, inter-VLAN routing occurs internally on that switch via SVIs. Therefore, the configuration of trunk ports between switches is irrelevant to troubleshooting inter-VLAN communication issues within a single Layer 3 switch.

  When this WOULD be correct

  This would be correct if the Layer 3 switch were connected to a separate Layer 2 switch via a trunk, and hosts in VLAN 10 and 20 could reach VLAN 30 through that trunk, but the trunk port on the Layer 2 switch did not have VLAN 30 allowed.

• ✓

  The SVI for VLAN 30 is missing an IP address.

  Why this is correct

  An SVI (Switched Virtual Interface) serves as the Layer 3 interface for a VLAN, acting as the default gateway for all devices within that VLAN. For inter-VLAN routing to function, each SVI must be configured with a unique IP address within its respective VLAN's subnet. If the SVI for VLAN 30 is missing an IP address, the Layer 3 switch cannot route traffic into or out of VLAN 30, effectively isolating it from other VLANs like VLAN 10 and VLAN 20.

• ✗

  The default gateway on hosts in VLAN 10 is incorrect.

  Why it's wrong here

  If the default gateway configured on hosts in VLAN 10 were incorrect, those hosts would be unable to send traffic to any destination outside their local VLAN 10, including both VLAN 20 and VLAN 30. The problem statement implies a specific issue with reaching VLAN 30, suggesting that communication with VLAN 20 might still be functional. A broad connectivity failure for VLAN 10 hosts to all external networks would indicate an incorrect default gateway, not a targeted issue with a single VLAN.

  When this WOULD be correct

  In a scenario where hosts in VLAN 10 cannot communicate with any other VLAN (e.g., VLAN 20 and VLAN 30), but hosts within VLAN 10 can communicate, the first thing to verify would be the default gateway configuration on the hosts in VLAN 10.

• ✗

  The routing table does not have a route to VLAN 30.

  Why it's wrong here

  While a missing route to VLAN 30 in the routing table would indeed prevent inter-VLAN communication, the most common and direct cause for a directly connected VLAN's route to be absent is an unconfigured or administratively down SVI for that VLAN. A Layer 3 switch automatically adds a connected route to its routing table once an SVI is configured with an IP address and is in an 'up/up' state. Therefore, verifying and correctly configuring the SVI is the foundational step before troubleshooting the routing table for directly connected networks.

  When this WOULD be correct

  This option would be correct in a scenario where a Layer 3 switch has SVIs for all VLANs with correct IPs, but static or dynamic routing is not configured to reach a remote VLAN (e.g., VLAN 30 is on a different router). The technician must verify the routing table for a route to that subnet.

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?”

Go deeper

Related to this question