lution that could compete. Hence, Cisco did the smartest thing it could do at the time-it acquired the best of the new switch- ing companies, like Kalpana, and added their devices to the Cisco lineup. As a result, Cisco switches did not have the same operating system that their routers did. While Cisco routers used the Internetwork Operating System (IOS), the Cisco switches sometimes used menus, or an operating system called CatOS. (Cisco calls its switch line by the name Catalyst; thus, the Catalyst Operating System was CatOS.) A quick word about terminology is in order. The words "switching" and "switch" have multiple meanings, even in the networking world. There are Ethernet switches, frame-relay switches, layer-3 switches, multilayer switches, and SO on. Here are some terms that are in common use: Switch The general term used for anything that can switch, regardless of discipline or what is being switched. In the networking world, a switch is generally an Ethernet switch. In the telecom world, a switch can be many things. Ethernet switch Any device that forwards frames based on their layer-2 MAC addresses using Ethernet. While a hub repeats all frames to all ports, an Ethernet switch forwards frames only to the ports for which they are destined. An Ethernet switch creates a collision domain on each port, while a hub generally expands a collision domain through all ports. Layer-3 switch This is a switch with routing capabilities. Generally, VLANs can be configured as virtual interfaces on a layer-3 switch. True layer-3 switches are rare today; most switches are now multilayer switches. Multilayer switch Same as a layer-3 switch, but may also allow for control based on higher layers in packets. Multilayer switches allow for control based on TCP, UDP, and even details contained within the data payload of a packet. Switching In Ethernet, switching is the act of forwarding frames based on their destination MAC addresses. In telecom, switching is the act of making a connection between two parties. In routing, switc