100-150 Question 193
Select 3A network administrator is troubleshooting an issue where devices in VLAN 10 cannot communicate with devices in VLAN 20. The switches involved are configured with MAC address filtering, and the administrator notices that some MAC addresses are not appearing in the MAC address table of Switch A. Which of the following actions should the administrator take to resolve the issue?
- A
Verify that MAC address filtering rules on Switch A are allowing traffic from devices in VLAN 10 and VLAN 20.
- B
Check if the interfaces assigned to VLAN 10 and VLAN 20 are in an 'up' state on Switch A.
- C
Ensure that VLAN 10 and VLAN 20 are configured with trunk ports on Switch A to allow inter-VLAN communication.
- D
Manually add the MAC addresses of devices in VLAN 10 and VLAN 20 to Switch A's MAC address table.
- E
Enable dynamic MAC address learning on Switch A to populate its MAC address table automatically.
Show answer and explanation
Correct answers: A, B, E
Explanation
The issue described involves devices not appearing in the MAC address table and communication failures between VLANs. Verifying MAC address filtering rules (Option 1) ensures that traffic is not being blocked at the switch level. Checking interface status (Option 2) confirms that the VLANs are operational. Enabling dynamic MAC address learning (Option 5) allows the switch to populate its MAC address table automatically, resolving the issue of missing MAC addresses. Trunk ports (Option 3) and manually adding MAC addresses (Option 4) are not directly relevant or effective in this scenario.
- A. Correct.
MAC address filtering rules can prevent certain devices from communicating across VLANs if the rules are misconfigured. Verifying these rules is critical to ensure proper traffic flow.
- B. Correct.
If the interfaces assigned to VLANs are in a 'down' state, devices in those VLANs will not be able to communicate. Checking the interface status is a necessary step in troubleshooting.
- C. Incorrect.
Trunk ports are used to carry traffic for multiple VLANs between switches, but they do not directly resolve the issue of devices not appearing in the MAC address table. This option is not directly relevant to the problem described.
- D. Incorrect.
Manually adding MAC addresses is not a practical or scalable solution, as MAC address tables are designed to be dynamically populated. This option is not recommended.
- E. Correct.
Enabling dynamic MAC address learning ensures that the switch automatically learns and updates its MAC address table as devices communicate. This is a key step in resolving the issue.