You connect a new host to a switch port, but the host cannot log in to or reach a server that is plugged into another port on the same switch. Routing is not involved. Which of the following is the most likely cause of the connectivity problem?

Introduction / Context:
In VLAN aware switched networks, devices that are supposed to communicate at layer 2 must be in the same VLAN. Even if they are connected to the same physical switch, if their ports are assigned to different VLANs, their traffic is kept logically separate and will not reach each other without routing. This scenario is very common when a new host is added to a network and the switch port is left in a default VLAN or misconfigured. The question tests your understanding of VLAN membership and its impact on basic host connectivity.

Given Data / Assumptions:

• A new host is connected to a switch port.
• A server is connected to another port on the same switch.
• The host cannot log in to or reach the server.
• No mention is made of inter VLAN routing or use of a router for this connection.
• The issue is likely confined to layer 2 configuration on the switch.

Concept / Approach:
Switch ports belong to VLANs, and all ports in the same VLAN form a single broadcast domain. Hosts in the same VLAN can communicate directly at layer 2, assuming IP settings such as subnet and gateway are consistent. If two hosts are in different VLANs on the same switch, they require layer 3 routing between those VLANs to communicate. When a new host cannot reach a server, and both are supposed to be on the same subnet and VLAN, a common cause is that the new port is assigned to the wrong VLAN. Correcting VLAN membership for that port usually restores connectivity.

Step-by-Step Solution:
1. Recognize that both devices are on the same physical switch, so physical connectivity is present. 2. Since the problem description does not involve a router, focus on layer 2 issues such as VLAN membership. 3. Understand that if the host port is in VLAN 10 and the server port is in VLAN 20, they are in separate broadcast domains and cannot communicate without routing. 4. Check the port configuration with commands like show interfaces switchport to verify the VLAN assignment. 5. Realize that the most likely problem is that the new host port is not in the correct VLAN that the server uses. 6. Conclude that the wrong VLAN membership on the host port is the most probable cause.

Verification / Alternative check:
In real troubleshooting, you would verify the IP configuration on the host and server to ensure they are in the same subnet. Then you would inspect the switch port configuration for both devices. If the server port is in VLAN 10 and the host port is in VLAN 1, ARP requests from the host for the server will never reach the server because they are isolated by VLAN boundaries. Changing the host port to VLAN 10 and testing again usually restores connectivity, confirming that VLAN mismatch was the root cause.

Why Other Options Are Wrong:
Option a: The problem statement says both devices are on the same switch and does not involve routing, so a missing router route is unlikely to be the cause. Option b: VTP (VLAN Trunking Protocol) is used to distribute VLAN definitions between switches, not to assign ports to VLANs. In a single switch scenario, port membership is a more direct concern. Option c: Invalid MAC addresses are extremely rare in normal hosts, and even if a MAC were unusual, it would not prevent the switch from forwarding based on that address as long as it is unique. Option e: The STP mode used by the switch does not affect whether two ports in the same VLAN can communicate under normal conditions, unless a port is blocked, which the question does not suggest.

Common Pitfalls:
A frequent mistake is assuming that as long as devices are on the same physical switch, they can talk to each other. In VLAN environments, logical segmentation is what matters. Another pitfall is focusing exclusively on IP settings and routing when the real issue is at layer 2. Always verify VLAN membership and trunk status when a host cannot reach another device on the same switch. This habit will save time in both exam questions and practical troubleshooting tasks.

Final Answer:
The most likely cause is that the switch port the host is connected to is not configured with the correct VLAN membership to match the server.