Network Bridge overview
The network bridge provides an inexpensive and easy way to connect local area network (LAN) segments. To understand how the network bridge works, it is important to understand what a LAN segment is. A LAN segment is a single section of network media that connects computers. For example, suppose you have three computers: computer A, computer B, and computer C. Computer A has two Ethernet network adapters, and computers B and C have one Ethernet network adapter each. An Ethernet cable connecting A to B would create one LAN segment. An additional Ethernet cable connecting A to C would create a LAN segment.
Traditionally, if you want to have a network that has more than one segment, you have two options: routing or bridging. IP routing is a common solution for connecting network segments. However, to set up for IP routing you need either to buy hardware routers or set up the computers at the junctions between segments to operate as routers. IP routing requires difficult configurations for IP addressing for each computer on each network segment, and each network segment needs to be configured as a separate subnet IP routing is a good solution for large networks, where scalability is important, and where there is an experienced staff to configure and maintain the network. A hardware bridging solution does not necessitate difficult configurations, like IP routing, but it does require that you purchase additional hardware bridges. Neither of these options are ideal if you have a home or small office network, do not want to purchase expensive bridging hardware, and do not have experienced staff to administer an IP routing network.
The network bridge, in contrast, allows you to connect LAN segments by selecting the appropriate network connection icons and clicking Bridge Connections. Similar buttons allow you to enable the bridge and add connections to it. The network bridge manages your LAN segments and creates a single subnet for the entire network. There is no configuration required, and you do not need purchase additional hardware such as routers or bridges. IP addressing, address allocation, and name resolution is highly simplified in a single subnet IP network.
The network bridge can create connections between different types of network media. In a traditional network, if you are using mixed media types you need a separate subnet for each type of media, and packet forwarding is required between each one of the network's multiple subnets. Packet forwarding is required because different protocols are used for different types of media. Network Bridge automates the configuration that is required in order to forward information from one type of media to another.
Only one bridge may exist on a Windows XP computer, but it can be used to bridge as many different network connections as the computer can physically accommodate. For information about creating a network bridge, see Bridge Connections
Spanning tree algorithm
Network Bridge uses the IEEE spanning tree algorithm (STA) to establish a loop-free forwarding topology. When there are multiple paths in a bridged network, loops can form and the simple forwarding rules of a bridge can cause forwarding storms, a condition in which the same frame is relayed endlessly form one bridge to another. STA provides an automated mechanism to selectively disable bridge forwarding on individual ports as is necessary in order to ensure that the forwarding topology is loop-free. There is no configuration necessary to configure the network bridge for the spanning tree algorithm.