Question

A network technician connects two Cisco switches to carry traffic for multiple VLANs across a single physical link. On SW1, the interface is configured with 'switchport mode trunk'. A colleague asks how frames belonging to VLAN 20 are distinguished from VLAN 30 as they traverse this link. What mechanism does 802.1Q use to accomplish this?

Accepted Answer

It inserts a 4-byte tag containing the VLAN ID into the Ethernet frame header.

Answer

It encapsulates each frame inside an additional IP header carrying the VLAN ID.

Answer

It sends VLAN membership information in a separate CDP advertisement before each frame.

Answer

It appends a 26-byte ISL header and trailer to encapsulate the original frame.