To Identify the VLAN to which a packet belongs and change tagging to assign a numeric value to each frame in a multi-VLAN network. This ensures that the switches know which ports to send.
The top list contains two VLANs, namely VLAN 3 and VLAN 4. Host A sends a shipping packet to SW1. Switch SW1 receives the packet, identifies the packet with VLAN ID 3, and sends it to SW2. SW2 receives the packet, searches for VLAN ID, and passes only the Fa0 / 1 packet because only this port is in VLAN 3. Host B and Host C do not receive the packet because they are in a VLAN other than Host A.
Think of the following network topology.
The top list contains two VLANs, namely VLAN 3 and VLAN 4. Host A sends a shipping packet to SW1. Switch SW1 receives the packet, identifies the packet with VLAN ID 3, and sends it to SW2. SW2 receives the packet, searches for VLAN ID, and passes only the Fa0 / 1 packet because only this port is in VLAN 3. Host B and Host C do not receive the packet because they are in a VLAN other than Host A.