Introduction of the bridge
Bridge is like a smart repeater. The repeater receives signals from one network cable, amplifies them, and sends them to the next cable. They do this for no purpose and don't care about the content of the messages they forward. In comparison, the bridge is more sensitive to the information uploaded from the level.
The bridge connects two similar networks and manages the flow of network data. It works at the data link layer, not only can extend the distance or range of the network, but also can improve the performance, reliability and security of the network. After network 1 and network 2 are connected by a bridge, the bridge receives the data packet sent by network 1 and checks the address in the packet. If the address belongs to network 1, it discards it. On the contrary, if it is the address of network 2, Continue to send to network 2. In this way, the network bridge can be used to isolate information, divide the network into multiple network segments, and isolate the secure network segment to prevent illegal access by users in other network segments. Due to the segmentation of the network, each network segment is relatively independent, and the failure of one network segment will not affect the operation of another network segment.
The network bridge can be a dedicated hardware device, or it can be realized by the network bridge software installed on the computer. At this time, multiple network adapters (network cards) will be installed on the computer.
The functions of the bridge are:
The function of the bridge is similar to a repeater in extending the network span, but it can provide intelligent connection services, that is, forwarding and filtering based on which network segment the frame end address is in. The bridge's understanding of the network segment of the site is achieved by "self-learning".
When using a bridge to connect two segments of LAN, the bridge must first check the destination address of the MAC frame from segment 1. If the frame is destined for a station on segment 1, the bridge does not forward the frame to segment 2, but filters it out; if the frame is destined for a station on segment 2, the bridge Then forward it to network segment 2. This shows that if there is a pair of users on LAN1 and LAN2 communicating at the same time on this network segment, it is obviously achievable. Because the bridge has played a role of isolation. It can be seen that the bridge has the effect of increasing the network bandwidth under certain conditions.
Compared with the repeater, the storage and forwarding function of the bridge has advantages and disadvantages. The advantages are:
Using bridges for interconnection overcomes physical limitations, which means that the total number of data stations and network segments that make up the LAN can easily be expanded.
The bridge's storage and forwarding capabilities make it suitable for connecting two LANs using different MAC protocols. Therefore, a mixed network environment in which different LANs are connected together is formed.
The relay function of the bridge only depends on the address of the MAC frame, so it is completely transparent to high-level protocols.
The bridge divides a larger LAN into segments, which helps improve reliability, availability, and security.
The main disadvantages of the bridge are:
Because the bridge receives and buffers frames before performing forwarding, it introduces more delay than the repeater.
Because the bridge does not provide flow control function, it may overload the traffic when there is heavy traffic, resulting in frame loss.
The advantages of the bridge over the disadvantages are the reasons for its widespread use.
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