Routing is divided into static routing and dynamic routing, and its corresponding routing table is called static routing tables and dynamic routing tables. The static routing table is pre-set according to the system installation, and the network administrator modifies the routing table after the network structure changes. Dynamic routing changes with the changes in the network operation, the router automatically calculates the optimal path of data transmission based on the functionality provided by the routing protocol, thereby obtaining a dynamic routing table. Depending on the routing algorithm, the dynamic routing protocol can be divided into distance vector routing protocol and link status routing protocol (Link State Routing Protocol). The distance vector routing protocol is based on the Bellman-Ford algorithm. It mainly has RIP, IGRP (IGRP for Cisco's private protocol); link status routing protocol is based on the very famous Dijkstra algorithm in Figure, the shortest Path First, SPF Algorithm, such as OSPF. In the distance vector routing protocol, the router passes some or all of the routing tables to the router adjacent to it; and in the link status routing protocol, the router passes the link status information to all routers in the same area. Depending on the location of the router in the Autonomous System (AS), the routing protocol can be divided into internal gateway protocols (Interior Gateway Protocol, IGP) and External Gateway Protocol, EGP, also called domain routing protocols. There are two domain routing protocols: External Gateway Protocol (EGP) and Boundary Gateway Protocol (BGP). EGP is designed for a simple tree topology, which has obvious disadvantages when handling selection cycles and setup routing policies, and is currently replaced by BGP. EIGRP is a private protocol of Cisco, a mixed protocol, which is characterized by a distance vector routing protocol, and inherits the advantages of the link status routing protocol. Various routes are all characterized, suitable for different types of networks. The following is set forth below. Forward the best path to the optimal path to find the diameter. The router is first lookup in the routing table, and it is determined that you know how to send the packet to the next site (router or host), if the router does not know how to send the packet, it usually discards the packet; otherwise groups according to the corresponding entry of the routing table Send to the next site, if the destination network is connected directly to the router, the router is sent directly to the corresponding port. This is the routing forwarding protocol (ROUTED Protocol). Routing forwarding protocols and routing protocols are mutually cooperative and independent concepts. The former uses the latter maintained routing table, and the latter should use the functionality provided by the former to issue routing protocol data packets. The routing protocols mentioned below unless otherwise stated, it is the routing protocol, which is also a common habit.
