Static and dynamic internal routing system in Campus Network

Two routers in an autonomous system are mutually internal routers. For example, because the core is an autonomous system, the two Internet core routers are mutually internal routers. The two routers on the university campus are also internal routers, because all the machines on the campus belong to the same autonomous system.
How does a router in an autonomous system obtain information about the network in the system? In a small, slowly changing Interconnect Network, managers can manually create and modify routes. The Administrator keeps a table about the network and updates the table when a new network is added to the autonomous system or a network is deleted from the autonomous system. Routing for such an interconnection network is negligible because there is only one route between any two points. The administrator can manually configure routes for all hosts and routers. When the status of the interconnect network changes, such as adding a new network, the manager reconfigured routes on all machines.

The artificial system has obvious disadvantages. It cannot adapt to the rapid growth or rapid changes of the network. In a large and rapidly changing environment, such as the Internet, people are too slow to respond to changes in the situation and cannot handle problems. an automatic mechanism must be used. The automatic mechanism can also improve the reliability and take response measures for faults in some small interconnected networks with changeable routes.

After vror5 R5 is added, a backup path is added between network 2 and network 3. When the original route fails, the routing software can quickly switch to the standby route.

For an interconnected network architecture with multiple physical paths, the Administrator usually chooses one of them as the basic path. If the router on the basic path fails, you must change the route so that the communication traffic is transmitted through the slave router. It takes a long time to manually change the routing mode and is prone to errors. Therefore, even in a small Internet connection, it is necessary to use a mechanism to quickly and reliably change the route.

To automatically save accurate network accessibility information, internal routers need to communicate with each other, that is, the routers and the other routers that can arrive must exchange network accessibility data or network routing information. After the reachable information of the autonomous system is collected, a vro 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 widely used standard for external router communication, but internal router communication does not have a separate standard. One of the reasons for this is the topological structure of the Autonomous System and the diversity of specific technologies. Another reason is the compromise between simple structure and powerful functionality, that is, protocols that are easy to install and configure often do not provide powerful functionality. Therefore, there are many popular protocols for internal router communication, but most autonomous systems only choose one of them to disseminate routing information internally.

Since there are no separate standards, we use the internal Gateway Protocol IGP (Interior Gateway Protocol) as a general term to describe all the network accessibility information for internal routers to exchange and routing information algorithms. For example, the Butterfly core router forms a specific autonomous system, which uses SPREAD as its internal gateway protocol IGP. Some autonomous systems use EGP for IGP, but it does not make much sense for small autonomous systems consisting of LAN with broadcast functions.

IGP1 and IGP2 indicate the internal gateway protocols used by autonomous systems 1 and 2, respectively.

Important concepts:

A single router can use two routing protocols at the same time. One is used for communication outside the autonomous system, and the other is used for communication within the autonomous system.

Specifically, for vrouters that run EGP to advertise accessibility, an IGP is usually required to obtain information within the autonomous system.

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