What is the best solution to prevent a user from sending a double-tagged 802.1q frame to a switch?

What is the best solution to prevent a user from sending a double-tagged 802.1q frame to a switch?

• A. Allow all VLANs on user access ports
• B. Set the native VLAN to match user access ports
• C. The VLANs for user access ports should differ from any native VLAN used on trunk ports
• D. Disable VLAN tagging altogether

Answer: (C)

The best solution to prevent a user from sending a double-tagged 802.1q frame to a switch is to ensure that the VLANs assigned to user access ports are different from any native VLANs used on trunk ports. This approach effectively mitigates the risk of VLAN hopping attacks where a malicious user sends a double-tagged frame. When a switch receives a double-tagged frame (which is a frame with two VLAN tags), it inspects the outer tag first. If the outer tag matches the native VLAN configured on the trunk port, the switch will remove this tag and forward the untagged frame based solely on the inner tag. If the native VLAN on the trunk matches the VLAN of a user access port, a user can craft a frame that will bypass the normal VLAN segmentation and gain access to the target VLAN. By having different VLAN configurations for user access ports and trunk port native VLANs, it becomes impossible for an attacker to construct a valid double-tagged frame that will be accepted and processed correctly by the switch. This configuration ensures proper traffic isolation and enhances network security by preventing unauthorized VLAN access. Implementing this strategy proactively safeguards the switch network against VLAN hopping exploits, ensuring that each VLAN remains properly segmented based on intended configurations.

The best solution to prevent a user from sending a double-tagged 802.1q frame to a switch is to ensure that the VLANs assigned to user access ports are different from any native VLANs used on trunk ports. This approach effectively mitigates the risk of VLAN hopping attacks where a malicious user sends a double-tagged frame.

When a switch receives a double-tagged frame (which is a frame with two VLAN tags), it inspects the outer tag first. If the outer tag matches the native VLAN configured on the trunk port, the switch will remove this tag and forward the untagged frame based solely on the inner tag. If the native VLAN on the trunk matches the VLAN of a user access port, a user can craft a frame that will bypass the normal VLAN segmentation and gain access to the target VLAN.

By having different VLAN configurations for user access ports and trunk port native VLANs, it becomes impossible for an attacker to construct a valid double-tagged frame that will be accepted and processed correctly by the switch. This configuration ensures proper traffic isolation and enhances network security by preventing unauthorized VLAN access.

Implementing this strategy proactively safeguards the switch network against VLAN hopping exploits, ensuring that each VLAN remains properly segmented based on intended configurations.