Network textbooks combine RIP, HELLO, and EGP

We have found that the same vro uses IGP to obtain routing information within the autonomous system, while the same vro uses EGP to notify other Autonomous Systems of routing information. Theoretically, it is easy to compile a software to implement these two protocols so that it can collect routes and advertise routes without manual intervention. However, due to technical and policy obstacles, it is very difficult to practice.

Technically, the IGP protocol is the same as RIP and HELLO protocol. Vrouters use this Protocol to obtain information about other vrouters in the autonomous system to update their routing tables. Unlike the internal Router Protocol, EGP also performs other work in addition to the usual routing table. The vro running EGP communicates with other Autonomous Systems for reachable information. It is independent of its own routing table. In this way, a UNIX program of RIP is routed, which notifies the information obtained from the local selector table and changes the local selector table when receiving the update information. It is correct to trust the data sent by the machine running RIP. On the contrary, the program implementing EGP does not advertise the route obtained from the local routing table; it retains an independent database for the accessible information of the network.

When the vro running EGP advertises reachable information, you must note that only authorized advertised routes can be transmitted. Otherwise, other parts of the interconnected network will be affected. For example, a route in an autonomous system occasionally broadcasts a non-existent route with a distance of 0 to the University of Perdu, the RIP Protocol will allow other routers to recognize this route and transfer the communication traffic to the faulty router. In this way, the communication traffic of the autonomous system where these routers are located cannot reach the university. If EGP broadcasts this error to a machine outside the autonomous system, some parts of the interconnected network will not be able to reach the university of Perdu.

The gated Program combines multiple IGP and EGP rules to broadcast routes to external routers according to a series of restrictions to form a whole. For example, gated can receive RIP packets and modify the route table of the local machine as the routed program. It uses EGP to advertise the routes accessible from the local autonomous system. These rules allow administrators to specify which networks can be advertised. Therefore, although the gated program is not a member of the IGP protocol family, it plays an important role in the routing process, it demonstrates that it is feasible to establish an automatic mechanism to link IGP and EGP without sacrificing security performance.

Another performance of the Gated program is to convert distance measurement standards. Specifically, the distance used when the vro inside the Autonomous System advertises a route is under a fixed limit of 128. The distance measurement used by the external router to advertise routes that span autonomous systems but have not exceeded the Autonomous System Consortium must be converted to a high range of 128 to 191 ), such a conversion mechanism artificially increases the cost of routing outside the autonomous system, so that the traffic flow within the autonomous system as much as possible. Finally, for routes beyond the Autonomous System Consortium, the distance value is converted to a higher range of 192 to 254) so as to make the traffic flow within the Autonomous System Consortium as much as possible. As the gated program provides interfaces between autonomous systems, this conversion operation can be easily implemented.