Bridging is a forwarding technique for the transmission of packet-switched messages between two LANs or LAN segments separated by a bridge. Bridging is performed at the linklayer, whereas routing, which is also a path-selection function, is performed at the network layer above it.
In bridging, hardware addresses are determined by flooding and checking the source address contained in the header and stored in a table. The technique is limited to local networks by flooding. Data packets are transmitted by MAC address, whereas in routing they are transmitted by IP address. Bridges can therefore not distinguish networks. If a host in a bridge network is connected to another network segment, it is not reconfigured. Routing is different, where the host in another network requires a new IP address.
The many different bridging variants have been standardized by the IEEE working group802.1. There are various bridging methods, especially for Ethernet, but also for Token Ring. For example, transparent bridging (TRB) or source route bridging( SRB). Since the MAC addresses do not have to be converted in bridging, the technique is faster than routing and is increasingly being used in data center networks. In terms of known, standardized techniques, there is Data Center Bridging( DCB) with the various methods used in it, such as Shortest Path Bridging ( SPB) or Shortest Path Backbone Bridging (SPBB).
Bridging is not limited to wired local networks, but can also take place in WLANs. This is wireless bridging, which is described in IEEE 802.11c. This standard deals with the wireless coupling of two networks via a WLAN. In wireless bridging, the access points(APs) of the WLANs establish a dedicated radio link between each other via the MAC address.