14.5 Routing with dynamic routes

The idea of static routes works nicely for very small numbers of routers, but what happens if the network is very large? There needs to be a way of making routers learn about each other automatically rather than the network administrator having to keep entering the details manually each time the network changes in some way.

This type of routing is called dynamic routing as opposed to static routing.

There are several routing protocols which have been developed to allow routers to learn about each other’s networks. Examples of these protocols include open-source protocols such OSPF and BGP, but we are going to look at a simple routing protocol called RIP (Routing Information Protocol) as it is about the simplest one to setup and demonstrate in the lab.

First we need to remove all the static routing we entered previously. Again we will do this by re-entering the ip route commands with a ‘no’ in front of them.

To configure RIP on each router we need to start the RIP protocol going with the command router rip. There are two versions of the RIP protocol for IPv4 – we need to use version 2 as version 1 is now obsolete. This is why we normally type the command version 2 whenever we type the router ripcommand.

To finish the configuration of RIP, we need to enter a network statement for each network that is local to our routers.

On Router1 enter the following statements: network 192.168.1.0, network 192.168.2.0and network 10.10.10.0on Router1. We now need to go to the command-line interface of Router2 and enter network 172.16.1.0and network 10.10.10.0.

If we now do a show ip route command on each router, we will see that there are some new routes in the routing table with a capital R next to them. This shows that they have been learned by the RIP protocol.

Just to prove everything is working, we will now do some pings from PC to PC to see the response. We can see that PC3 can ping PC1, and PC3 can also ping PC2.

Just to prove that routing protocols make our lives simpler than doing all the work manually, we are now going to add in a new network. We will create PC4 and join it to the gigabit 0/2 interface of Router2. We will then add the IP address of PC4 as 172.16.2.2.

We then give the gigabit 0/2 interface the IP address of 172.16.2.1, and then not forget to switch the interface on.

All we need to do to make this new network show up round the whole system, is to finally enter the new network statement of network 172.16.2.0 on Router2. To do this, type router ripto enter the RIP configuration mode. We do not need to type version 2again as it has already been entered previously. We then enter the command network 172.16.2.0.

If we now go to Router1 and look at its routing table again, we will now see that the new network has appeared in the routing table and there are now two networks which have been learned by RIP.

You should now have some understanding about the roles of static routing and dynamic routing, and have some idea of the situations in which you would use each type of routing.