Bridges may also be single port, which connect two segments, or multiport which connect several segments. When a bridge sees a packet, it checks the packet's destination address against its internal list. If the address indicates the packet needs to be forwarded to another segment, it passes the packet to the other segment. If the bridge doesn't know where the receiving station is located, it sends it to the other segment anyway. Changes in the network require that the bridge be re-programmed.
Simple bridges are inexpensive, but are a lot of bother to maintain.
Learning Bridge- this bridge builds its table over time. As messages are sent, the new bridge makes note of the source address and segment of the sending workstation. From then on, it knows where to send messages addressed to that station. Eventually, it builds a complete table of source addresses. That is, unless a workstation never sends a message.