Quick Start of RIP Routing Protocol

In network routing protocols, RIP is one of the most important protocols. Then we can quickly learn this protocol based on the way the router works. The routing mode is very easy to understand. It works in almost two ways: Path Selection and data forwarding, the difficulty is how to determine the optimal path to the target network. Therefore, path selection is the most important task of the router ｡

Many routing protocols can be used to select routes, such as RIP, OSPF, IGRP, and OSPF. In these algorithms, we cannot simply say who is better or worse, because the advantages and disadvantages of an algorithm must be determined based on the environment in use, such as the RIP Protocol, which sometimes cannot accurately select the optimal path, and the convergence time is somewhat longer, but for small-scale, for a network without professional maintenance personnel, it is the preferred routing protocol, and we are looking at its simplicity ｡

If you have a small network project, let's arrange a plan to read this article (one read) in 30 minutes ), I will go over the commands and operation methods mentioned in this article in 20 minutes (two-read), and configure all the routers on the network in 30 minutes (small networks, few vrouters can be configured ), in the last 20 minutes, check whether the network is working properly. Okay. In the last 20 minutes, your RIP network is running. It's that simple. Don't believe it. Please continue ｡

What is the RIP routing protocol?

RIP (Routing Information Protocols) is the most widely used distance vector protocol, which was developed by Xerox in 1970s, RIP is part of the Xerox Network Service (Xerox Network Service) protocol cluster. The TCP/IP version of RIP is the license version of Xerox protocol, both the implementation principle and configuration method are very simple ｡

Measurement Method

The RIP measurement is based on the number of hops (hops count). Each time a router passes through, the number of hops in the path increases by one. As a result, the longer the number of hops, the longer the path, the RIP algorithm gives priority to the path with a few hops. the maximum number of hops supported by RIP is 15, and the number of hops is 16 ｡

Route update

Route updates in RIP are implemented through scheduled broadcast. By default, the router broadcasts its route table to the network connected to RIP every 30 seconds, the router that receives the broadcast adds the received information to its route table. Each router is broadcast so that all the routers on the network will know all the route information. Normally, the router receives a route message confirmation every 30 seconds. If a route entry is not confirmed after 180 seconds, that is, six update cycles, the router considers it to have expired. If the route entry remains unconfirmed after 240 seconds, that is, eight update cycles, it will be deleted from the routing table, the latency of 180 seconds and 240 seconds is controlled by the Timer. They are the Update Timer, Invalid Timer, and Flush Timer )｡

Routing cycle

Distance vector algorithms are prone to route loops. RIP is a distance vector algorithm, so the RIP routing protocol is no exception. If there is a route loop on the network, information will be transmitted cyclically, to avoid this problem, the RIP equi-distance vector algorithm implements the following four mechanisms ｡

Horizontal segmentation ensures that the router remembers the source of each route information, and do not send it again on the port that receives this message. This is the most basic measure to ensure that no route loop is generated ｡

Poison reverse. When a path becomes invalid, the router does not immediately delete it from the routing table, but uses 16, that is, an inaccessible measurement value broadcasts it out. Although this increases the size of the route table, it is helpful to eliminate the routing cycle and can immediately clear any loops between neighboring routers ｡

Trigger update. When the route table changes, the update packet is immediately broadcast to all adjacent routers, instead of waiting for a 30-second update cycle, when a router initiates RIP, it broadcasts the request message. The adjacent router that receives the broadcast immediately responds to an update message, instead of waiting for the next update cycle, changes in the network topology will spread over the network as quickly as possible, reducing the possibility of Route loops ｡

Holddown timer. After a route entry is invalid, the route entry is in the suppression State for a period of time, that is, it no longer receives route updates for the same destination address within a certain period of time. If, A vro learns that a path is invalid from one CIDR block, and then immediately learns that the route is valid on the other CIDR block. This valid information is often incorrect. suppressing timing avoids this problem, in addition, when a link starts and stops frequently, the suppression timing reduces the floating speed of the route, and the RIP route protocol increases the network stability ｡