Bridging is standard by the IEEE 802.1 Working Group.

Bridging is an Interconnection that creates a single aggregate logical network from multiple communication networks or network segments.

Bridging is performed Data-link Layer where Routing is performed at the Network Layer.

Bridging has a few different Classifications

  • Transparent bridging uses a table called the forwarding information base to control the forwarding of frames between network segments. The table starts empty and entries are added as the bridge receives frames. If a destination address entry is not found in the table, the frame is flooded to all other ports of the bridge, flooding the frame to all segments except the one from which it was received. By means of these flooded frames, a host on the destination network will respond and a forwarding database entry will be created. Both source and destination addresses are used in this process: source Network Address are recorded in entries in the table, while destination addresses are looked up in the table and matched to the proper segment to send the frame to
  • simple bridge connects two network segments, typically by operating transparently and deciding on a frame-by-frame basis whether or not to forward from one network to the other.

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