The most common interface on a Cisco router is the Ethernet or FastEthernet interface. It has the form of a female RJ-45 connector.
In order to make it work we must configure it and enable it. Some of the configuration parameters are the interface ip address and the subnet mask.
Let’s say that in our router with the name ROUTER we must configure the Fast Ethernet 0/0 with the ip address 192.168.1.1 and the subnet musk 255.255.255.0
First we have to log in the router. We may be asked for the username and the password or just the password or nothing at all (specially in new routers).
Then, we must use the enable command to enter the privileged EXEC mode where we are able to change the router configuration.
After entering the privilege EXEC mode, we must apply the command configure terminal in order to enter the router’s configuration mode.
To enter to the area of the FastEthernet 0/0 configuration we enter the interface fastethernet 0/0 command.
To set up the proper ip address to the interface we apply the command ip address 192.168.1.1 255.255.255.0
At last we must activate the interface. So, we apply the no shutdown command.
That’s it. The interface has the ip address configured and is activated. We use the Ctrl+z keys combination to exit the configuration mode and the logout command to logout the router.
This is the whole procedure display in our terminal.
We use the ping and the traceroute command to the proper pc or laptop to verify the interface functionality and the connectivity with the router.
Good luck!