Processing of dial-up network routing in RIP Protocol

In view of the characteristics of the dial-up network routing, it is impossible for us to regularly broadcast the routing on the dial-up network for 30 seconds, just like on the LAN and the leased line network, thus, we cannot process the timeout of the route on the dial-up network like the route on the LAN.

Based on this consideration, in order to ensure the timeliness and feasibility of the route, we stipulate that the route modification packet on the dial-up network should be sent in the following situations:

1. When receiving a specific request for Route modification;
2. When the routing database is changed by the new route message received from another interface;
3. When you know that a sink is reachable;
4. When an interface goes DOWN from circuit to circuit UP

This has such a problem: RIP messages are sent through UDP port 520, while UDP is an unreliable transmission mode. This obviously requires consideration of the possibility of packet transmission failure. To this end, we adopt a re-transmission and confirmation mechanism for message transmission during transmission. When a request message is sent, if the sender fails to receive the confirmation message sent by the sender within five seconds after the request message is sent or modified, the sender resends the request message or confirmation message. If no confirmation message is received five seconds after the resend, the resend continues until the sender receives the confirmation message. If, after 10 resends, the system considers that the message has been sent to the DDH, the transmission fails and the Metric value of the corresponding route is set to 16. When receiving a message, when receiving a request or modification message from the source, you must confirm the received message and send the corresponding confirmation message to the original source.
If a route modification packet is received from the router of the next station on the dial-up network, the route entry in the modified packet will always be considered reachable until a route message fails to be sent.

The difference between the Dialing Network and the LAN and the leased line network for timeout processing is also reflected in the routing database. In a routing database, there are two types of routes: "temporary routing" and "permanent routing ". "Temporary routing" is applicable to lan routing and Wan leased line routing. This route is broadcast every 30 seconds, and timeout processing is performed after the route refresh packet is not received within a certain period of time. "Permanent routing" refers to a route that includes a dial-up network. No timeout processing is performed if no refresh message is received, however, if a message fails to be sent to a sink, the route is changed to a "temporary route ". Another scenario is to change "permanent routing" to "temporary routing", which will be discussed later.

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• RIP Distance Vector Algorithm

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