Routing refers to the process of determining the network scope of the end-to-end path when a packet travels from the source to the destination. Routing works at the third layer of the OSI reference model-the packet forwarding device at the network layer. The router realizes network interconnection by forwarding data packets. Although routers can support multiple protocols (such as TCP/IP, IPX/SPX, AppleTalk, etc.), most routers in my country run TCP/IP protocol. A router usually connects two or more logical ports identified by an IP subnet or point-to-point protocol, and has at least one physical port. The router determines the output port and next hop address according to the network layer address in the received data packet and the routing table maintained inside the router, and rewrites the link layer data packet header to forward the data packet. The router reflects the current network topology by dynamically maintaining the routing table, and maintains the routing table by exchanging routing and link information with other routers on the network.

Routing is the activity of transferring information from a source address to a destination address through an interconnected network. Routing occurs at the third layer of the OSI network reference model, the network layer. The routing guides the packet forwarding, after passing through some intermediate nodes, to their final destination. If it is made into hardware, it is called a router. Routing usually guides the forwarding of packets based on a routing table—a table that stores the best paths to various destinations. Therefore, in order to efficiently forward packets, it is very important to establish a routing table stored in the router's memory. The difference between routing and bridging is that routing assumes that nodes with similar addresses are close to each other. This allows a record in the routing table to indicate the path to a group of addresses. Therefore, in large-scale networks, routing is better than bridging, and routing has become the most important method for finding paths on the Internet. Smaller networks can usually set the routing table manually, but larger networks with complex topologies may often change, and it is impractical to manually set up the routing table. Despite this, most public switched telephone networks (PSTN) still use pre-calculated routing tables, and only use the prepared path when the directly connected path is disconnected; see Public Switched Telephone Network Routing. "Dynamic routing" attempts to automatically build a routing table based on the information carried by the routing protocol to solve this problem, and also allows the network to avoid network disconnection or failure almost autonomously. Dynamic routing currently dominates the entire Internet. However, setting up routing protocols often requires experience and technology; current network technology has not yet been developed to be able to set up routes automatically. A packet-switched network (such as the Internet) divides data into many packets with a complete destination address, and each packet is forwarded separately. The circuit-switched network (such as the public switched telephone network) also uses routing to find a path so that the following data can reach the correct destination even with only part of the destination address.

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