A networking component used either to extend or to segment networks. Bridges work at the OSI data-link layer. They can be used both to join dissimilar media such as unshielded twisted-pair (UTP) cabling and fiber-optic cabling, and to join different network architectures such as Token Ring and Ethernet.
Bridges regenerate signals but do not perform any protocol conversion, so the same networking protocol (such as TCP/IP) must be running on both network segments connected to the bridge.
Bridges can also support Simple Network Management Protocol (SNMP), and they can have other diagnostic features.
The three basic types of bridge.
Bridges come in three basic types:
Bridges operate by sensing the source MAC addresses of the transmitting nodes on the network and automatically building an internal routing table. This table is used to determine which connected segment to route packets to, and it provides the filtering capability that bridges are known for. If the bridge knows which segment a packet is intended for, it forwards the packet directly to that segment. If the bridge doesn’t recognize the packet’s destination address, it forwards the packet to all connected segments except the one it originated on. And if the destination address is in the same segment as the source address, the bridge drops the packet. Bridges also forward broadcast packets to all segments except the originating one.
Use bridges to reduce network congestion and improve performance by segmenting busy Ethernet networks into smaller collision domains. Bridges can also be used to connect segments more efficiently than repeaters and to join dissimilar networks such as Ethernet and token ring. Remote bridges can be used to create WAN links.
A poorly placed bridge can actually worsen network performance. For example, if you use a bridge to divide users who belong to the same department and frequently communicate with each other over the network, this might actually slow down communication among users by creating a bottleneck. It is better to use bridges to join separate departmental LANs together on which intradepartmental traffic is greater than interdepartmental traffic.
When using bridges to connect networks, make sure that only one path leads to any destination node on the network; otherwise, frames could become locked in loops and circle the network endlessly, causing a network storm.