To connect to a terminal for initial configuration
It is used to manage the router.
console port
Console port is used
CPU RAM Flash memory Console port fast Ethernet port
console port
A rollover cable is typically used to connect from a DB9 serial port on your computer to the RJ45 console port on the router. An RJ45-RJ45 rollover can be used from Aux port to Console port or from the ports on a 2509-RJ/2511-RJ to a console port.
If you connect to the router via the console port then you are physically making a connection with a physical cable to the router. This implies you have to be close to the router itself. Using telnet allows you to connect to the router from anywhere in the network, and doesn't require a physical cable connection.
make a connection from the router's console port to your laptop's serial port and configure the router from your laptop.
Should you start a Cisco router sans config (as is the case when you first purchase it), then it will not do anything but power on - yet. You must attach a cable to the console port of the router on one end, and the serial port of your computer at the other. This can also be done using a rollover cable to connect the router's console port to your computer's ethernet port. Once connected, you can use HyperTerminal, Cutecom, or another serial communication terminal program to see the console input.output from the router. It will ask you if you would like to enter the initial configuration script. Type yes and work from there!
console
Rollover
HyperTerminalMinicom
console