Editing Network switch (section)

== Bridging ==
[[File:Smartswitch6000.jpg|thumb|A modular network switch with three network modules (a total of 36 Ethernet ports) and one power supply]]
[[File:5 Port Gigabit Netzwerk-Switch TL-SG1005D 01.jpg|alt=A five-port layer-2 switch without management functionality|thumb|A five-port layer-2 switch without management functionality]]

Modern commercial switches primarily use Ethernet interfaces. The core function of an Ethernet switch is to provide multiple ports of layer-2 bridging. Layer-1 functionality is required in all switches in support of the higher layers. Many switches also perform operations at other layers. A device capable of more than bridging is known as a multilayer switch.

A layer 2 network device is a multiport device that uses hardware addresses ([[MAC address]]es) to process and forward data at the data link layer (layer 2).

A switch operating as a network bridge may interconnect otherwise separate layer 2 networks. The bridge learns the MAC address of each connected device, storing this data in a table that maps MAC addresses to ports. This table is often implemented using high-speed [[content-addressable memory]] (CAM), some vendors refer to the MAC address table as a CAM table.

Bridges also buffer an incoming packet and adapt the transmission speed to that of the outgoing port. While there are specialized applications, such as storage area networks, where the input and output interfaces are the same bandwidth, this is not always the case in general LAN applications. In LANs, a switch used for end-user access typically concentrates lower bandwidth and [[uplink]]s into a higher bandwidth.

The Ethernet header at the start of the frame contains all the information required to make a forwarding decision, some high-performance switches can begin forwarding the frame to the destination whilst still receiving the frame payload from the sender. This [[cut-through switching]] can significantly reduce latency through the switch.

Interconnects between switches may be regulated using the [[spanning tree protocol]] (STP) that disables forwarding on links so that the resulting local area network is a [[Tree (graph theory)|tree]] without [[switching loop]]s. In contrast to routers, spanning tree bridges must have topologies with only one active path between two points. [[Shortest path bridging]] and [[TRILL]] (Transparent Interconnection of Lots of Links) are layer 2 alternatives to STP which allow all paths to be active with multiple equal cost paths.<ref>{{cite web
 |title        = Shortest Path Bridging IEEE 802.1aq Overview
 |publisher    = Huawei
 |author       = Peter Ashwood-Smith
 |date         = 24 Feb 2011
 |url          = http://meetings.apnic.net/__data/assets/pdf_file/0012/32007/APRICOT_SPB_Overview.pdf
 |access-date   = 11 May 2012
 |archive-url  = https://web.archive.org/web/20130515115628/http://meetings.apnic.net/__data/assets/pdf_file/0012/32007/APRICOT_SPB_Overview.pdf
 |archive-date = 15 May 2013
 |url-status     = dead
 |df           = dmy-all
}}</ref><ref>
{{cite news
 |title = IEEE Approves New IEEE 802.1aq Shortest Path Bridging Standard
 |publisher = Tech Power Up
 |date = 7 May 2012
 |url = http://www.techpowerup.com/165594/IEEE-Approves-New-IEEE-802.1aq-Shortest-Path-Bridging-Standard.html
 |access-date = 11 May 2012
 }}</ref>