Inter VLANs Communication

Typically, a router is required for communication among devices in different VLANs. Bridges or Switches cannot forward traffic from one VLAN to another. In most network environments, each VLANs is associated with a network or a subnet address. In an IP network, usually a subnet number is associated with an individual VLAN.

When a node (workstation) in one VLAN sends a packet to a node (workstation) in another VLAN,  interVLAN communication (or routing) takes place. One or more routers are required for inter VLAN communication.

Consider two VLANs, VLAN 100 and VLAN 200. 

When a node on VLAN 100 (Node A) needs to send a packet to Node B on VLAN 200, then the VLAN switch associated with VLAN 100 needs to forward the packet to a Router. The router in turn routes the packet to the associated VLAN switch. The VLAN switch, in turn, forwards the packet to Node B.

When a packet is destined for a node within a VLAN, there is no routing required. The packet is directly forwarded to the associated node by the Switch.