14.3 Routing with static routes

The reason why the ping from PC1 to PC3 still does not work is because we don’t have a return path created in the reverse direction for the traffic to come back.

To solve this we need to put the default static route command into Router2 as well, to direct unknown traffic from Router2 to be sent to Router1. We will put the command ip route 0.0.0.0 0.0.0.0 10.10.10.1into Router2, which will direct traffic for unknown networks in Router2 back to FRouter1’s address.

OK, so let’s try the ping again. Now when we ping 172.16.1.2 from PC1 we should expect a reply.

From this we have learned that you need to set up both the outward path and a return path between the two routers. Default static routes are really only useful where there is only one router connected to another – such as in the network topology we have used here, or with your home or business broadband connection. Default static routes are useful where there is only one choice of destination to send the traffic to.

With bigger networks we need a different approach to setting up the routing tables. One solution could be to use static routes – where we set up the path to each destination network manually.

First we are going to remove the default static routes we created on both Router1 and Router2. To do this we need to execute the same command we used to put the default route in, but enter the word ‘no’ at the beginning of the command.

OK, let’s look at the following command on Router1: ip route 172.16.1.0 255.255.255.0 10.10.10.2.

This has put in a path to network 172.16.1.0 (with a subnet mask of 255.255.255.0) sending the traffic to the IP address of 10.10.10.2 – which is Router2’s address. We must not forget to put in the return path so that Router2 knows how to send the ping back to PC1. For this we will use the command ip route 192.168.1.0 255.255.255.0 10.10.10.1.

We now have a path out from PC1 to PC3, and a return back to the starting point. If we now try pinging PC1 from PC3, we can see that this works nicely. It should also work the other way round, so next we will ping PC1 from PC3. This works properly too.

OK, let’s try something else. Let’s see if PC3 can ping PC2. If we ping 192.168.2.2 from PC3, we get this result. We can see that it has failed. The reply was from 172.16.1.1 (which is Router2) and it says that the destination host is unreachable. Let’s look at Router2’s routing table to see what is going on: show ip route shows that the new network we manually entered to 192.168.1.0 and with a mask of 255.255.255.0 (which is represented as /24) is in the routing table.

We need to think about why PC3 and PC1 can ping each other, but not PCs 3 and 2.