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Ethernet Bridges

A bridge is solution to having too many computers all sharing the same segment of the network and consequently all seeing every other NIC's traffic. A bridge allows the network to be divided up in smaller but still connected segments. Traffic within these segments is isolated unless a request by one machine goes beyond its own segment and asks for communication with a NIC on another segment. The bridge keeps a small database of the MAC addresses it finds on each sub-segment and only relays between segments where required. This can make considerable improvements on network speed and get the benefits of segment isolation. A bridge can also be used to connect different topologies, for example star with a bus network.

A bridge is a simple solution to administer, as all the sub-segments are still one network. It is fast, as little processing is done on data packets passing through but is not that flexible in designing larger networks. As a Bridge has to process all packets on the network, it can also be overloaded. As well it does not provide increased security, nor use the flexibility that a Router provides by operating through the Data Control Layer (Layer 2 OSI Model) that TCP/IP provides. Usually Ethernet Bridges can be used with any network technologies e.g. Ethernet and Token Ring, but cannot be used to logically connect networks using different transport media together.

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