100-150 Question 189
Single answerA network administrator is troubleshooting a connectivity issue in a switched network. They notice that two devices in the same VLAN cannot communicate with each other. Upon investigation, the administrator discovers that both devices are connected to the same switch but are on separate switch ports. What could be causing this issue?
- A
The devices are configured with IP addresses in different subnets.
- B
The switch ports are configured as access ports in different VLANs.
- C
The switch has Spanning Tree Protocol (STP) enabled, which is blocking one of the ports.
- D
The switch does not have enough MAC address table entries to forward traffic.
Show answer and explanation
Correct answer: B
Explanation
Switches use VLANs to segment network traffic into isolated broadcast domains. If two devices are connected to different VLANs, even on the same switch, they cannot communicate with each other without routing between the VLANs. Ensuring that the switch ports are in the same VLAN is critical for devices to communicate within the same broadcast domain.
- A. Incorrect.
While devices in different subnets cannot typically communicate without routing, this is not relevant in this case since the issue pertains to switching and VLAN configuration.
- B. Correct.
If the switch ports are configured as access ports in different VLANs, the devices will not be able to communicate because VLANs segment traffic, and devices in different VLANs require a router or Layer 3 switch to communicate.
- C. Incorrect.
STP is used to prevent network loops, and while it can block ports, this scenario does not suggest a loop or STP-related issue.
- D. Incorrect.
A full MAC address table can cause issues in forwarding traffic, but this would typically result in broader network problems, not just between two specific devices.