This Fast Ethernet (100Mbps) expansion module is a dual-port interface that is used to establish a connection between Catalyst switches and high-speed devices, such as servers or routers. Each of the dual-ports can be configured as Fast Ethernet or ISL mode. ISL is used to interconnect VLAN-capable Fast Ethernet devices to network servers, or to high-performance backbone devices such as Fast Ethernet hubs, switches, and routers. The ISL protocol tags a standard Ethernet frame with the VLAN information associated with that frame. VLAN packet tagging allows networks to contain VLAN trunks.