An online Protocol for specified packet transfer Mode

The main node device of the Internet is the router, which forwards the
received data through the routing table. in networks with smaller scale,there is no problem of manually specifying the forwarding strategy. However, if the forwarding strategy is specified manually in a large-scale network, it will bring huge workload to the network administrator, and it becomes very difficult to manage and maintain the routing table. Dynamic routing protocols allow routers to automatically learn from the network of other routers, and automatically update the routing table after the network
topology changes. Network administrators only need to configure the dynamic routing protocol, compared with the manual specified forwarding policy, the workload is greatly reduced.

Function: provides a mechanism for the interconnection of heterogeneous networks

Principle: sharing routing information between routers
Common routing protocols

(1)  RIP(Route Information Protocol): is the simplest routing protocol, which mainly transmits routing information, maintains the location relationship of adjacent routers by broadcasting routing table every 30 seconds, and calculates its own routing table information according to the routing table information received

(2)  IGRP(Interior Gateway Routing Protocol): Developed independently by cisco in the 1980s, it belongs to cisco private protocol. IGRP is characterized by the use of mixed measures, taking into account the bandwidth, delay, load and mtu, reliability of the link to calculate the metrics of routing, rather than simply considering one aspect of the measures of other IGP protocols.

(3)  EIGRP belongs to advanced distance vector routing protocol. It inherits the mixed measure of IGRP. The biggest characteristic is that it introduces non-equivalent load balancing technology and has very fast convergence speed.

(4)  OSPF(Open Shortest Path First):belongs to the link state routing protocol. OSPF uses the maintained link status database to compute the routing table. OSPF converges faster. due to its unique openness and good scalability, currently the OSPF protocol is widely deployed in various networks.

(5)  IS-IS(Intermediate system to intermediate system):Belongs to the link-state routing protocol. Standard is-is not suitable for IP network, so IETF has developed an integrated IS-IS protocol for IP network. Like OSPF, IS-IS also uses the concept of "area", also maintains a link-state database, and calculates the best path through SPF. IS-IS converges faster. Integrated IS-IS protocol is the most commonly used IGP protocol in ISP backbone network.