Basic Cisco Router RIP Configuration

Cisco Router RIP Configuration

This article is next in a series of articles covering the basics of Cisco networking. This article takes a look at the configuration of the Routing Information Protocol (RIP). While RIP is rarely seen in production networks anymore it is a good starting point for those just getting familiar with network routing protocols.

RIP has been around for a long time but has not been seen as the main routing protocol in production networks for a while. This is mainly because the protocol is slow to converge and is limited to a maximum of 15 total routing hops. These hops are also what RIP uses as a metric. This is one of the reasons why RIP is one of the first routing protocols that many people learn.

RIP, like all distance vector routing protocols, does not provide the participating device (router) with a picture of the whole network. RIP devices only need to have a database which contains how to next route a packet to a neighbor. That neighbor will then use its own database for where to send it next. This is commonly referenced as routing-by-rumor because each device is using only the data from the neighboring devices to form the RIP routing table.

There are two version of RIP (for IPv4) that are available: version 1 and version 2. Version 1 utilized a broadcast packet to advertise the known RIP routes to neighbors. However what was not included in this update was the subnet mask length. Because of this, RIP version 1 does not support any type of variable length mask. With RIP version 2, support became available for variable length masks as well as a change from using a broadcast packet to using a multicast packet.

Because RIP itself is rather simple the configuration of RIP is just as easy. The first step is to gain access to the device and access global configuration mode. If this process is not familiar check out the first article in this series on Cisco device setup. Once this mode has been accessed the prompt should look like Figure 1.

global configuration mode

Figure 1 – Global Configuration Mode

To configure RIP the first step is to create a RIP routing instance. This is done with the ‘router rip’ command, which is shown in Figure 2.

creating a RIP router instance

Figure 2 – Creating a RIP Router Instance

The next part requires some knowledge of the networks that will be advertised from this device. For the purposes of this example, the 192.168.1.0/24 network will be advertised by RIP on this device. The command that is required for this is ‘network network,’ which is shown in Figure 3.

configure the advertised RIP network

Figure 3 – Configure the Advertised RIP Network

At this point RIP, will begin advertising its connectivity to the 192.168.1.0/24 network.  However this is assuming that an enabled interface exists on this device that is using the 192.168.1.0/24 network. If the interface has not been configured yet then RIP will wait until it is configured and enabled.

If the configured interface used a mask other than /24 (for 192.168.1.0) it would not matter as RIP version 1 only supports classful networks (192.168.1.0). What this means is that regardless of the configured mask on the interface it will be advertised as 192.168.1.0/24. If variable sized masks need to be supported than RIP version 2 is required.  The command to configure RIP version 2 is ‘version 2’ and this is shown in Figure 4.

RIP version 2 configuration

Figure 4 – RIP Version 2 Configuration

Once this command is entered, RIP will advertise the exact mask that is configured on the interface regardless if it is classful (/24) or classless (/25../32).

Summary

The configuration of RIP on routers is commonly completed by those just getting into the network field and who are learning the base concepts of routing protocols. RIP offers an easy configuration and allows a new student to understand how these protocols communicate while also using easy to reference metrics. Hopefully the content in this article will help the reader understand routing protocols.

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