What is Bridge?

A network bridge is a computer networking device that makes one combination network from multiple communication networks or network segments. This function is termed network bridging. Bridging is distinct from routing, as routing allows multiple totally different networks to communicate severally while remaining separate while bridging connects 2 separate networks as if they are just one network (hence the name "bridging"). in the OSI model, bridging is performed within the 1st 2 layers, below the network layer (layer 3).If one or a lot of segments of the bridged network are wireless, the device is known as a wireless bridge and the operate as wireless bridging.

There are four sorts of network bridging technologies: simple bridging, multiport bridging, learning or transparent bridging, and source route bridging


Simple bridging
A simple bridge connects 2 network segments, generally by operating transparently and deciding on a frame-by-frame basis whether or not to forward from one network to the other. A store and forward technique is usually used so, during forwarding, the frame integrity is verified on the source network and CSMA/CD delays are accommodated on the destination network. Contrary to repeaters that simply extend the maximum span of a segment, bridges only forward frames that are needed to cross the bridge. additionally, bridges scale back collisions by partitioning the collision domain.

Multiport bridging
A multiport bridge connects multiple networks and operates transparently to decide on a frame-by-frame basis whether or not and wherever to forward traffic. just like the simple bridge, a multiport bridge generally uses store and forward operation. The multiport bridge function is the basis for network switches.

Transparent bridging
A clear bridge uses a forwarding info to send frames across network segments. The forwarding database starts empty - entries within the database are built because the bridge receives frames. If an address entry isn't found within the forwarding info, the frame is flooded to all different ports of the bridge, flooding the frame to all or any segments except the one from which it was received. By means that of those flooded frames, the destination network can respond and a forwarding info entry are created.

In the context of a two-port bridge, one will think of the forwarding info as a filtering info. A bridge reads a frame's destination address and decides to either forward or filter. If the bridge determines that the destination node is on another segment on the network, it forwards (retransmits) the frame to that section. If the destination address belongs to a similar section because the supply address, the bridge filters (discards) the frame. As nodes transmit knowledge through the bridge, the bridge establishes a filtering info of known mac addresses and their locations on the network. The bridge uses its filtering database to see whether or not a frame should be forwarded or filtered.

Transparent bridging also can operate over devices with quite 2 ports. As an example, consider a bridge connected to 3 hosts, A, B, and C. The bridge has 3 ports. A is connected to bridge port one, B is connected to bridge port two, C is connected to bridge port three. A sends a frame addressed to B to the bridge. The bridge examines the source address of the frame and creates an address and port range entry for A in its forwarding table. The bridge examines the destination address of the frame and doesn't realize it in its forwarding table thus it floods it to all different ports: two and three. The frame is received by hosts B and C. Host C examines the destination address and ignores the frame. Host B recognizes a destination address match and generates a response to A. On the come path, the bridge adds an address and port range entry for B to its forwarding table. The bridge already has A's address in its forwarding table so it forwards the response solely to port one. Host C or the other hosts on port three don't seem to be burdened with the response. Two-way communication is currently possible between A and B without any more flooding in network.

Both supply and destination addresses area unit employed in this algorithm: supply addresses area unit recorded in entries within the table, whereas destination addresses area unit hunted within the table and matched to the correct section to send the frame to.