Bridges are Layer 2 devices that forward data frames according to the MAC address. Bridges read the sender's MAC address of the data packets that are received on the incoming ports to discover which devices are on each segment. The MAC addresses are then used to build a bridging table. This will allow the bridge to block packets that do not need to be forwarded from the local segment. 

Although the operation of a bridge is transparent to other network devices, the latency on a network is increased by ten to thirty percent when a bridge is used. This latency is a result of the decision making process prior to the forwarding of a packet. A bridge is considered a store-and-forward device. The bridge must examine the destination address field and calculate the cyclic redundancy check (CRC) in the frame check sequence field before forwarding the frame. If the destination port is busy, the bridge can temporarily store the frame until that port is available.