Static and dynamic internal routing system of Campus network

The two routers within an autonomous system are each other's internal routers. For example, because the core constitutes an autonomous system, two Internet core routers are internal routers. The two routers on the university campus are also internal routers, because all machines on campus belong to the same autonomous system.

How does a router in an autonomous system get information about the network within the system? In a small, slowly changing interconnection network, managers can use the manual way to establish and modify the route. The manager retains a table about the network and updates the form when a new network joins the autonomous system or deletes a network from the autonomous system. It is trivial to choose a path for such an interconnection network because there is only one route between any two points. Managers can configure all the routing of hosts and routers in a human way. When the interconnection network changes state (for example, a new network), the manager reconfigure the routes on all machines.

The artificial system is obviously flawed, and it cannot adapt to the rapid growth or rapid change of the network. In large, rapidly changing environments, such as the Internet, people react too slowly to changes in conditions that are too late to handle problems; You must use automated mechanisms. The adoption of automated mechanisms also facilitates reliability and responds to failures in small interconnected networks with variable routing.

Increased router R5 makes the network between 2 and 3 more than a standby path when the original route out of fault, the routing software can quickly switch to standby routing for the Interconnection network architecture with multiple physical paths, the manager usually chooses one of them as the basic path. If the router on the base path fails, the route must be altered to allow traffic to be transmitted over the standby router. The way you manually change the route takes a long time and can easily lead to errors. Therefore, even in a small interconnect, you should use a dynamic mechanism to change routing quickly and reliably.

In order to automatically save accurate network information, the internal routers to communicate between the router and the other reachable routers to exchange network accessibility data or network routing information. After pooling the reachable information of the entire autonomous system, one of the routers in the system uses EGP to advertise them to another autonomous system.

The difference between internal router communication and external router communication is that EGP provides a standard for the widespread use of communications for external routers, while internal router communication does not have a single standard. One of the reasons for this is the topological structure of autonomous systems and the diversity of specific technologies. Another reason is the tradeoff between simple structure and powerful functionality, where protocols that are easy to install and configure often do not provide powerful functionality. Therefore, there are many kinds of protocols that are popular for internal router communication, but most autonomous systems only select one of them to propagate the routing information.

Because there is no separate standard, we use the Internal Gateway Protocol IGP (Interior Gateway Protocol) as a general term to describe all the network accessibility information and routing information for the exchange between internal routers. For example, the butterfly core router constitutes a specific autonomous system that uses spread as its internal gateway protocol IGP. Some autonomous systems use EGP for IGP, but this has little meaning for small autonomous systems consisting of broadcast-enabled LANs.

IGP1 and IGP2 represent the internal gateway protocols used by autonomous Systems 1 and 2, respectively.

Important Concept:

A single router can simultaneously use two routing protocols, one for communication outside of the autonomous system and the other for internal communication within the autonomous system.

Specifically, a router that runs the EGP notification accessibility usually needs to run a IGP to get information inside its autonomous system.