How does a network bridge function?

A network bridge connects multiple network segments, allowing them to communicate as if they were a single network.

A network bridge, also known as a bridging hub, switch, or switching hub, is a device that connects multiple network segments at the data link layer (layer 2) of the OSI model. Its primary function is to receive incoming network traffic and then decide whether to forward or discard it, based on the device's MAC address. This process is known as frame forwarding.

The bridge maintains a forwarding table, which is a database of MAC addresses and their associated network segments. When a frame arrives, the bridge checks the destination MAC address against its forwarding table. If the address is in the table, the bridge forwards the frame to the appropriate segment. If the address is not in the table, the bridge forwards the frame to all segments except the one it came from. This is known as flooding.

Bridges also have a learning function. When a frame arrives, the bridge notes the MAC address of the sending device and the segment it came from. If this information is not already in the forwarding table, the bridge adds it. This allows the bridge to build up a picture of which devices are on which segments, improving its forwarding decisions over time.

Bridges can also use the Spanning Tree Protocol (STP) to prevent loops in the network. Loops can cause broadcast storms, where a single frame is endlessly forwarded around the network, consuming bandwidth and potentially causing a network failure. STP allows bridges to detect loops and block certain paths to prevent this from happening.

In summary, a network bridge is a crucial device in networking that connects multiple network segments, allowing them to communicate as if they were a single network. It does this by forwarding frames based on their destination MAC addresses, learning the location of devices over time, and using STP to prevent network loops.