100-150 Question 194
Select 3A network administrator is troubleshooting a connectivity issue in a VLAN-enabled network. They notice that one VLAN cannot communicate with another VLAN, and some devices are not receiving traffic even though their MAC addresses are learned in the switch's MAC address table. Which of the following actions should the administrator take to resolve the issue?
- A
Verify that the switch ports are assigned to the correct VLANs.
- B
Check if MAC address filtering is enabled and blocking traffic for certain devices.
- C
Ensure that an inter-VLAN routing mechanism, such as a router-on-a-stick configuration, is properly configured.
- D
Clear the MAC address table to allow the switch to relearn the MAC addresses of connected devices.
- E
Disable VLAN tagging on trunk ports to simplify communication between VLANs.
Show answer and explanation
Correct answers: A, B, C
Explanation
To resolve the issue, the administrator needs to ensure that the VLAN configurations are correct (assigning ports to the correct VLANs), verify that no MAC address filtering is unintentionally blocking traffic, and confirm that inter-VLAN routing is properly configured. These steps address the key causes of VLAN isolation and connectivity failures. Clearing the MAC address table or disabling VLAN tagging would not resolve the issue and could introduce further problems.
- A. Correct.
If switch ports are not assigned to the correct VLANs, devices in one VLAN will not be able to communicate with devices in another VLAN. This is a common misconfiguration that can cause VLAN isolation issues.
- B. Correct.
MAC address filtering, if improperly configured, can block traffic for specific devices. Checking this setting ensures that no devices are unintentionally blocked from communicating.
- C. Correct.
Inter-VLAN communication requires a routing mechanism, such as a Layer 3 device or router-on-a-stick configuration. Without this, devices on different VLANs cannot communicate.
- D. Incorrect.
Clearing the MAC address table is generally unnecessary unless there are known issues with stale or incorrect entries. It is not a primary troubleshooting step for VLAN or inter-VLAN communication issues.
- E. Incorrect.
Disabling VLAN tagging on trunk ports will disrupt VLAN communication entirely, as trunk ports are necessary for carrying traffic from multiple VLANs between switches or to a router.