 Mbps is high enough for an indi- vidual workstation, there is no need to update the network interface card of that computer as long as the port of the switch supports that data rate. The two 10/100-Mbps switches are 10-Mbps switches that were upgraded with a network interface card that connects them at 100 Mbps to the higher-level switches in the network. In the same way, the highest-level switches were upgraded with 1,000-Mbps cards for their interconnections and for the Introduction to Telecommunications Network Engineering To other 100 Mbps Servers networks 1,000 Mbps 100/1,000 Mbps 100/1,000 Mbps switch switch 100/1,000 Mbps Router 100 Mbps 100 Mbps 100 Mbps 10/100 Mbps 10/100 Mbps switch switch 100 Mbps switch 100 Mbps 10 Mbps 100 Mbps 10 Mbps Figure 6.35 Ethernet network operating at 10, 100, and 1,000 Mbps. connections to the servers. In the next upgrade we would probably replace the highest-level switches with genuine Gigabit Ethernet switches and use the old ones to replace lower-level switches or repeaters. Ethernet technology is still evolving and it will soon support data rates of 10 Gbps. 6.5.12 Virtual LAN A large physical LAN can be divided into many logical LANs. This improves the performance and security of the LAN because the traffic of, for example, a marketing department is separated from other traffic because it is on a dedi- cated logical LAN. A straightforward way to define a virtual LAN (VLAN) is to say that all computers connected to a certain ports of a switch make up one logical LAN and traffic is switched between these ports only. Another more flexible way to configure a VLAN is to define the MAC addresses of all computers that belong to a certain network. This principle is more difficult to manage because a network manager has to define a VLAN for each MAC address. On the other hand, switches may dynamically config- ure themselves when a computer is transferred to a new physical location. This principle also allows a computer to belong to many VLANs. The third way to configure a VLAN