What are the main devices for interconnecting LAN and WAN?

The main device that realizes the interconnection between LAN and WAN is the "router". A router is a hardware device that connects two or more networks. It acts as a gateway between networks. It is a dedicated intelligent network device that reads the address in each data packet and then decides how to transmit it.

The operating environment of this tutorial: Windows 7 system, Dell G3 computer.

Routers are used to interconnect LAN and WAN.

A router is a hardware device that connects two or more networks. It acts as a gateway between networks. It reads the address in each data packet and then decides how to transmit it. Dedicated intelligent network equipment. It can understand different protocols, such as the Ethernet protocol used by a local area network and the TCP/IP protocol used by the Internet. In this way, the router can analyze the destination addresses of data packets from various types of networks, convert the addresses of non-TCP/IP networks into TCP/IP addresses, or vice versa; and then classify each data packet according to the selected routing algorithm. Deliver the best route to the specified location. So the router can connect non-TCP/IP networks to the Internet.

Function

The most important function of the router can be understood as the transfer of information. Therefore, we call this process the addressing process. Because the router is between different networks, it is not necessarily the final receiving address of the information. So in a router, there usually is a routing table. According to the final address of the information transmitted by the transmitting website, find the next forwarding address and which network it should be. In fact, to put it in a nutshell, it is like a courier company sending emails. The mail does not arrive at the final destination instantly. Instead, it is sorted at different substations and continuously approaches the final address, thereby realizing the mail delivery process. The router addressing process has a similar principle. Through the final address, a match is made in the routing table, and the next forwarding address is determined algorithmically. This address may be an intermediate address or the final destination address. [4]

The function of a router is to transmit data between different subnets. The specific functions are as follows:

(1) Realize the interconnection of IP, TCP, UDP, ICMP and other networks.

(2) Process the data. It can send and receive data packets and has various functions such as packet filtering, multiplexing, encryption, compression and protection wall of data.

(3) Select the next transmission destination of the data packet based on the information in the routing table.

(4) Exchange topology information between the external gateway protocol and other autonomous domains.

(5) Implement network management and system support functions.

Connecting different networks

From the perspective of filtering network traffic, the role of routers is very similar to switches and bridges. However, unlike switches that work at the network data link layer and physically divide network segments, routers use specialized software protocols to logically divide the entire network. For example, a router that supports the IP protocol can divide the network into multiple subnet segments, and only network traffic directed to special IP addresses can pass through the router. For each received packet, the router recalculates its checksum and writes a new physical address. Therefore, using a router to forward and filter data tends to be slower than a switch that only looks at the physical address of the packet. However, for those networks with complex structures, using routers can improve the overall efficiency of the network. Another obvious advantage of the router is that it can automatically filter network broadcasts. Generally speaking, the entire installation process of adding a router to the network is much more complicated than a plug-and-play switch.

Information transmission

Some routers only support a single protocol, but most routers can support the transmission of multiple protocols, that is, multi-protocol routers. Since each protocol has its own rules, completing the algorithms of multiple protocols in one router will inevitably reduce the performance of the router. The main job of the router is to find an optimal transmission path for each data frame passing through the router, and to effectively transmit the data to the destination site. It can be seen that the strategy for selecting the best path, that is, the routing algorithm, is the key to the router. In order to complete this work, data related to various transmission paths - a routing table (Routing Table) - is saved in the router for use in routing selection. The path table stores subnet identification information, the number of routers on the network, and the name of the next router. The path table can be fixed and set by the system administrator.

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