Bridging is a forwarding technique used in packet-switched computer networks. Unlike routing,
bridging makes no assumptions about where in a network a particular address is located. Instead,
it depends on flooding and examination of source addresses in received packet headers to locate
unknown devices. Once a device has been located, its location is recorded in a table where the
MAC address is stored so as to preclude the need for further broadcasting. The utility of bridging
is limited by its dependence on flooding, and is thus only used in local area networks.
Bridging generally refers to Transparent bridging or Learning bridge operation which
predominates in Ethernet. Another form of bridging, Source route bridging, was developed for
token ring networks.
A network bridge connects multiple network segments at the data link layer (Layer 2) of the OSI
model. In Ethernet networks, the term bridge formally means a device that behaves according to
the IEEE 802.1D standard. A bridge and switch are very much alike; a switch being a bridge with
numerous ports. Switch or Layer 2 switch is often used interchangeably with bridge.
Bridges are similar to repeaters or network hubs, devices that connect network segments at the
physical layer (Layer 1) of the OSI model; however, with bridging, traffic from one network is
managed rather than simply rebroadcast to adjacent network segments. Bridges are more
complex than hubs or repeaters. Bridges can analyze incoming data packets to determine if the
bridge is able to send the given packet to another segment of the network.
