an one VLAN. Figure 4-3 shows two switches connected with a trunk. Jack is connected to VLAN on Switch B, and Diane is connected to VLAN 20 on Switch A. Because there is a trunk connecting these two switches together, assuming the trunk is allowed to carry traffic for all configured VLANs, Jack will be able to communicate with Diane. Notice that the ports to which the trunk is connected are not assigned VLANs. These ports are trunk ports and, as such, do not belong to a single VLAN. Chapter 4: 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 Trunks also allow another possibility with switches. Figure 4-2 shows how two VLANs can be connected with a router, as if the VLANs were separate physical networks. Imagine you want to route between all of the VLANs on the switch. How would you go about implementing such a design? Traditionally, the answer would be to provide a single connection from the router to each network to be routed. On this switch, each network is a VLAN, SO you'd need a physical connection between the router and each VLAN. 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, users buy switches 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 VLAN 20 VLAN 30 VLAN 40 VLAN 10 VLAN 10 VLAN 20 E 0/0 Port 0 Port 1 Port 2 Port 3 Port 4 Port 5 Port 6 Port 7 Figure 4-4. Routing between multiple VLANs Connect