Recall that the logical topology of an Ethernet network is a multi-access bus in which devices all share access to the same medium. This logical topology determines how hosts on the network view and process frames sent and received on the network. However, the physical topology of most Ethernet networks today is that of a star or extended star. This means that on most Ethernet networks, end devices are typically connected, in a point-to-point basis, to a Layer 2 LAN switch.
A Layer 2 LAN switch performs switching and filtering based only on the OSI data link layer (Layer 2) MAC address. A switch is completely transparent to network protocols and user applications. A Layer 2 switch builds a MAC address table that it uses to make forwarding decisions. Layer 2 switches depend on routers to pass data between independent IP subnetworks.