Port 1 on a switch is part of VLAN 1, and port 2 is part of VLAN 200. If all of the switch ports were part of VLAN 1, the hosts connected to these ports could communicate. In this case however, the ports are part of different VLANs, VLAN 1 and VLAN 200. A router must be involved if hosts from the different VLANs need to communicate.

The most important benefit of routing is its proven history of facilitating networks, particularly large networks. Although the Internet serves as the obvious example, this point is true for any type of network, such as a large campus backbone. Because routers prevent broadcast propagation and use more intelligent forwarding algorithms than bridges and switches, routers provide more efficient use of bandwidth. This simultaneously results in flexible and optimal path selection. For example, it is very easy to implement load balancing across multiple paths in most networks when routing. On the other hand, Layer 2 load balancing can be very difficult to design, implement, and maintain.

If a VLAN spans across multiple devices a trunk is used to interconnect the devices. A trunk carries traffic for multiple VLANs. For example, a trunk can connect a switch to another switch, a switch to the inter-VLAN router, or a switch to a server with a special NIC installed that supports trunking.

Remember that when a host on one VLAN wants to communicate with a host on another, a router must be involved.

Interactive Media Activity Drag and Drop: Inter-VLAN Routing When the student has completed this activity, the student will learn the path packets take in a network with inter-VLAN routing. The student will predict the path a packet will take given the source host and the destination host.