There are three methods to access an IOS device: the console, Telnet, and SSH. Telnet and SSH enable access using the TCP/IP network on which the device resides, while the console access requires the physical access to the device. Here is a brief description of each method:
- the console access – typically used for the initial IOS configuration, this type of access uses a physical port on an IOS device to establish the connection. The physical port is usually located at the back of the device and is can be connected to a serial port on the PC using a rollover cable (image source: Cisco):
- the Telnet access – this type of access doesn’t require that you have the physical access to the device. Instead, you can access and configure the device over the TCP/IP network. To use Telnet, your PC needs to have a Telnet client installed. The IOS device needs to be configured as a Telnet server and have an IP address. Note that Telnet sends all data in clear text, so this method of access is not widely used anymore.
- the SSH access – like Telnet, this access type enables you to configure an IOS device remotely from your PC, but it adds an extra layer of security by encrypting all communications between devices. Your PC needs to have an SSH client installed (e.g. Putty), and the IOS device that is being accessed needs to be configured as an SSH server.