N10-009 Question 5
Single answerLayer 2 - Data linkA network administrator is replacing an unmanaged switch with a managed switch in a small office. After the cutover, users in the Finance department report they can no longer reach their accounting server, but users in other departments remain connected to their own resources. The accounting server is connected to switch port 12 and Finance users are connected to ports 1-8. The administrator verifies link lights are on and all devices have valid IP addresses. On the old switch, all ports were effectively in the same broadcast domain. On the new switch, ports 1-8 are assigned to VLAN 20, but port 12 is still in the default VLAN. Which action would MOST likely restore connectivity?
- A
Assign port 12 to VLAN 20 so the server and Finance user ports are in the same Layer 2 broadcast domain
- B
Configure port 12 with a static IP address in the same subnet as the Finance users
- C
Enable STP PortFast on ports 1-8 and port 12 to reduce forwarding delays
- D
Replace the patch cable connected to port 12 because VLAN mismatches commonly indicate a physical layer fault
Show answer and explanation
Correct answer: A
Explanation
This question tests practical Layer 2 switching knowledge, specifically VLAN behavior on managed switches. A VLAN creates a separate broadcast domain, so devices in different VLANs cannot communicate directly at Layer 2 without a Layer 3 device performing inter-VLAN routing. In this scenario, Finance clients were moved to VLAN 20, while the accounting server remained in the default VLAN, isolating it from those users. The proper fix is to assign the server's access port to VLAN 20 if the design intends for the server to be in the same Layer 2 segment as Finance. This aligns with standard Ethernet switching behavior and common vendor documentation for access port VLAN configuration on managed switches.
- A. Correct.
Correct. VLANs are a Layer 2 segmentation mechanism that create separate broadcast domains on a switch. If Finance user ports are in VLAN 20 but the accounting server's port remains in the default VLAN, frames from the users will not reach the server at Layer 2 unless inter-VLAN routing is configured. Placing port 12 in VLAN 20 restores same-VLAN communication and is the most direct fix for this scenario.
- B. Incorrect.
Incorrect. End devices such as servers receive IP addresses on their NICs, not on switch ports. Also, the scenario points to a Layer 2 VLAN membership issue, not an IP addressing problem. Even if the server has a valid IP address in the correct subnet, a VLAN mismatch can still prevent communication because the devices are isolated in different Layer 2 domains.
- C. Incorrect.
Incorrect. PortFast helps access ports transition to forwarding state more quickly when connecting end devices, but it does not solve traffic isolation caused by different VLAN assignments. The symptoms described are persistent for one department and one server, which aligns with a VLAN configuration issue rather than STP convergence delay.
- D. Incorrect.
Incorrect. A bad cable could cause loss of link or intermittent physical connectivity, but the administrator already confirmed link lights are on. A VLAN mismatch is a logical Layer 2 configuration issue, not a cabling fault. Replacing the cable would be a plausible troubleshooting step in some cases, but it is not the most likely solution here.