Bridge

Bridge is like a smart repeater. Repeaters in the network cable from a received signal, amplify them, and be sent to the next cable. In comparison, the bridge down from the level of information is more sensitive to upload some. Bridge is a kind of frame forwarding technology, according to MAC sub-blocks, can be isolated from the collision. Bridge over the network segment connecting the data link layer.
Bridge will connect two similar networks, and manage the flow of network data. It works on data link layer, not only to extend the network distance or range, and can improve network performance, reliability and security. Network 1 and Network 2 is connected by bridge, the bridge receives data packets sent network 1, checking the address of the packet, if the address belongs to the network 1, it will be a waiver, on the contrary, if the address of the network 2, it to continue to send to the network 2. This information can be isolated by a bridge, the network is divided into multiple network segments, isolated section of a safety net to prevent unauthorized access to other users of network segment. As the network segments, relatively independent of each segment, a segment of the fault will not affect the operation of another segment.
Bridge can be a specialized hardware device, you can also install the bridge by computer software to achieve, then the computer will be installed on multiple network adapters (network cards).
Bridge function is similar in extending the network span repeater, but it can provide intelligent connectivity services that, according to the frame at the end of the address to which to forward and filter network segment. Segment on which the bridge is the understanding of the site by "self learning" to achieve.
When connecting two LAN bridge, the bridge segment 1 from the MAC frame, first check the destination address. If the frame is sent to a station on the segment 1, the bridge is not forwarded to the frame segment 2, and to filter out; if the frame is sent to a station on the segment 2, the bridge It will be forwarded to segment 2, which suggests that if the LAN1 and LAN2 on each of a pair of users to communicate on the same section of this site is clearly achievable. Because the bridge played a role in isolation. It can be seen, the bridge has increased under certain conditions, the role of network bandwidth.
Bridges store and forward repeaters compared with the advantages and disadvantages, its advantages are:
Interconnection using bridges to overcome the physical limitations, which means that the data points constitute a LAN segment number of total and very easy to expand.
Bridge into the store and forward capabilities to adapt them to use different MAC protocol for connecting two LAN, and therefore constitute a different mix together the mixed LAN network environment.
Bridge relay function depends only on the MAC address of frames, thus completely transparent to higher layer protocols.
Bridge will be a large LAN into segments, will help to improve reliability, availability and security.
The main drawback is the bridge: the bridge in the implementation of the received frame before forwarding, and buffering, as compared with the repeater will introduce more delay. Since the bridge does not provide flow control function, so large has the potential to flow overload, resulting in the loss frame.
Bridge the pros outweigh the cons is the reason for their widespread use.
Bridge work in the data link layer, and the two LAN connected together, according to MAC address to forward the frame, can be seen as a "low level router" (routers work in the network layer, such as the IP address of the network address forwarding.)
Remote bridge is usually through a slow link (such as telephone lines) to connect two remote LAN,
The local bridge, the performance is more important, while the remote bridge is concerned, can be in the long-distance running is more important.
Comparison of bridge and router
Bridge did not understand the forward frame level protocol information, which it can handle the same way IP, IPX and other protocols, it also provides a free network routing protocols (such as NetBEUI) sub-function.
Since the router handling the network layer of the data, so they are easier to interconnect different data link layer, such as token ring segment and the Ethernet segment. Bridges are usually difficult to control than the router. Protocols such as IP routing protocols are complex, so easy to manage network routing; IP and other protocol also provides more information on how the network segment (even if the addresses provided such information.) But only with the MAC address and bridge the physical topology of the work. Therefore, generally for a small bridge over a simple network.