Bridge & Bridging (networking)

Bridge

A bridge is built to connect the two land masses. Since the car cannot swim or fly, the bridge makes it possible for automobiles to continue driving from one land mass to another.

In computer networking, a bridge serves the same purpose. It connects two or more local area networks (LANs) together. The cars, or the data in this case, use the bridge to travel to and from different areas of the network. The device is similar to a router, but it does not analyze the data being forwarded. Because of this, bridges are typically fast at transferring data, but not as versatile as a router. For example, a bridge cannot be used as a firewall like most routers can. A bridge can transfer data between different protocols (i.e. a Token Ring and Ethernet network) and operates at the "data link layer" or level 2 of the OSI (Open Systems Interconnection) networking reference model.

Bridges serve a similar function as switches, that also operate at Layer 2. Traditional bridges, though, support one network boundary, whereas switches usually offer four or more hardware ports. Switches are sometimes called "multi-port bridges" for this reason.


Bridging (networking)
Network bridging describes the action taken by network equipment to allow two or more communication networks, or two or more network segments, to create an aggregate network. Bridging is distinct from routing which allows the networks to communicate independently as separate networks. A network bridge is a network device that connects multiple network segments. In the OSI model bridging acts in the first two layers, below the network layer.


There are four types of network-bridging technologies: 
simple bridging; multiport bridging; learning, or transparent bridging; and source route bridging. Transparent bridging was originally developed by the Digital Equipment Corporation (DEC) in the 1980s.