belong to a single VLAN. Trunks also allow another possibility with switches. Figure 4-2 showed how two VLANs can be connected with a router, as if the VLANs were separate physical net- works. Imagine if you wanted to route between all of the VLANs on the switch. How would you go about such a design? Traditionally, the answer would be to provide a single connection from the router to each of the networks to be routed. On this switch, each of the networks is a VLAN, SO you'd need a physical connection between the router and each VLAN. Connecting VLANs Switch A Port 8 Port 9 Port 10 Port 11 Port 12 Port 13 Port 14 Port 15 VLAN 20 VLAN 30 VLAN 40 VLAN 10 VLAN 10 VLAN 20 Port 0 Port 1 Port 2 Port 3 Port 4 Port 5 Port 6 Port 7 Trunk Port 8 Port 9 Port 10 Port 11 Port 12 Port 13 Port 14 Port 15 Diane VLAN 20 VLAN 30 VLAN 40 VLAN 10 VLAN 10 VLAN 20 Port 0 Port 1 Port 2 Port 3 Port 4 Port 5 Port 6 Port 7 Switch B Figure 4-3. Two switches connected with a trunk As you can see in Figure 4-4, with this setup, four interfaces are being used both on the switch and on the router. Smaller routers rarely have four Ethernet interfaces, though, and Ethernet interfaces on routers can be costly. Additionally, switches are bought with a certain port density in mind. In this configuration, a quarter of the entire switch has been used up just for routing between VLANs. Port 8 Port 9 Port 10 Port 11 Port 12 Port 13 Port 14 Port 15 E 1/0 E 1/1 VLAN 20 VLAN 30 VLAN 40 VLAN 10 VLAN 10 VLAN 20 E 0/0 E 0/1 Port 0 Port 1 Port 2 Port 3 Port 4 Port 5 Port 6 Port 7 Figure 4-4. Routing between multiple VLANs Another way to route between VLANs is commonly known as the router on a stick configuration. Instead of running a link from each VLAN to a router interface, you can run a single trunk from the switch to the router. All the VLANs will then pass over a single link, as shown in Figure 4-5. Deploying a router on a stick saves a lot of interfaces on both the switch and the router. The downside is that the trunk is only one link, and the total band