Editing Multilayer switch (section)

== Layer-2 switching ==
[[Layer-2]] switching uses the [[MAC address]]es of the hosts’ [[network interface controller]]s (NICs) to decide where to forward frames. Layer-2 switching is hardware-based, which means switches use ASICs to build and maintain the [[forwarding information base]] and to perform [[packet forwarding]] at wire speed. One way to think of a layer-2 switch is as a multiport [[Bridging (networking)|bridge]].

Layer-2 switching is highly efficient because there is no modification to the frame required. Encapsulation of the packet changes only when the data packet passes through dissimilar media (such as from Ethernet to FDDI).  Layer-2 switching is used for workgroup connectivity and network segmentation (breaking up [[collision domain]]s). This allows a flatter network design with more network segments than conventional networks joined by [[repeater hub]]s and routers.

Layer-2 switches have the same limitations as bridges. Bridges break up collision domains, but the network remains one large [[broadcast domain]] which can cause performance issues and limits the size of a network. Broadcast and multicasts, along with the slow convergence of spanning tree, can cause major problems as the network grows. Because of these problems, layer-2 switches cannot completely replace routers. Bridges are good if a network is designed by the [[80/20 rule]]: users spend 80 percent of their time on their local segment.{{citation needed|date=October 2019}}