Which technique enables traffic to flow through any VLAN by manipulating Ethernet frame tags?

Which technique enables traffic to flow through any VLAN by manipulating Ethernet frame tags?

• A. VLAN hopping
• B. Switch Spoofing
• C. double tagging
• D. STP

Answer: (C)

Double tagging is the technique that lets traffic pass into other VLANs by tampering with Ethernet frame tags on a trunk. On 802.1Q trunks, frames are tagged with a VLAN ID, and the native VLAN is typically treated as untagged. In a double-tagging scenario, a frame carries two tags: the outer tag matches the native VLAN, and the inner tag specifies the target VLAN. The switch on the trunk edge removes the outer tag (as it’s the native VLAN) and then uses the remaining inner tag to forward the frame into the target VLAN, effectively hopping to that VLAN regardless of the port’s assigned VLAN. This is why it’s the best fit for “manipulating Ethernet frame tags” to cross VLAN boundaries. Other options don’t describe this tag-based traversal: VLAN hopping is the general idea of crossing VLANs, STP handles loop prevention, and switch spoofing involves impersonating a switch rather than manipulating VLAN tags. To defend, ensure consistent native VLAN handling on both ends of trunks and restrict trunk VLANs so frames aren’t inadvertently guided into unintended networks.

Double tagging is the technique that lets traffic pass into other VLANs by tampering with Ethernet frame tags on a trunk. On 802.1Q trunks, frames are tagged with a VLAN ID, and the native VLAN is typically treated as untagged. In a double-tagging scenario, a frame carries two tags: the outer tag matches the native VLAN, and the inner tag specifies the target VLAN. The switch on the trunk edge removes the outer tag (as it’s the native VLAN) and then uses the remaining inner tag to forward the frame into the target VLAN, effectively hopping to that VLAN regardless of the port’s assigned VLAN. This is why it’s the best fit for “manipulating Ethernet frame tags” to cross VLAN boundaries. Other options don’t describe this tag-based traversal: VLAN hopping is the general idea of crossing VLANs, STP handles loop prevention, and switch spoofing involves impersonating a switch rather than manipulating VLAN tags. To defend, ensure consistent native VLAN handling on both ends of trunks and restrict trunk VLANs so frames aren’t inadvertently guided into unintended networks.