Example 3: IEEE 802.1Q Tagging

ISW is able to construct Layer-2 broadcast domain by identifying VLAN (Virtual LAN) ID specified by IEEE 802.1Q. It forwards a frame between bridge ports assigned to the same VLAN ID and can set multiple VLANs on each bridge port.

In the following figure, the tagged incoming packets are assigned directly to VLAN 100 and VLAN 200 because of the tag assignment in the packet. Port 2 is configured as a tagged member of VLAN 100, and Port 7 is configured as an untagged member of VLAN 200. Hosts in the same VLAN communicate with each other as if they in a LAN. However, hosts in different VLANs cannot communicate with each other directly.

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In this case:

  1. The hosts from Group A can communicate with each other.
  2. The hosts from Group B can communicate with each other.
  3. The hosts of Group A and Group B can‘t communicate with each other.