10.1 Connecting to a Cisco device

In this part we will look at how to access the Cisco command-line interface. In Session 1 we looked at connecting to a home gateway; this was done with a GUI interface via a web page. By default, a Cisco device will not have a web page for configuration. With Cisco commercial networking equipment, the configuration is done via a CLI instead. The majority of manufacturers use the same principles in their own CLIs with slight variations on commands.

This is what the Cisco CLI looks like. It is part of the Cisco Internetwork Operating System or IOS for short. To connect to a device through the CLI you will need to use one of the following methods depending on the current status of the device. During the initial configuration of a device, or if the device is not accessible over the network, you will need to use a console connection. Whilst connected to the device a remote connection method should be set up, more likely Telnet or SSH. The serial connection, therefore, will no longer be needed as the router will now be accessed via its IP address. A username and password, however, will be required to gain access to the configuration options. The configuration of these protocols is shown in Session 15.

To connect to a device via the console port – normally indicated on Cisco devices with a pale blue colour – you will need a console cable also known as a Cisco rollover cable. This is a special cable with a different pin-out to Ethernet cables. On most routers this will need a serial console connection to a PC. If your computer doesn’t have a serial connector, you will need a USB converter as well. In my setup shown in the diagram, I have a USB-to-serial converter – that’s the grey cable – this is then connected to a Cisco rollover cable, the pale blue cable. These cables connect the PC’s USB port to the console port of the Cisco router. On newer routers the console connection can be a direct USB connection as well; you can see this in the picture here.

In a commercial environment where you are using physical equipment, this is where you would use a terminal emulation program such as Tera Term, PuTTY or SecureCRT. This software is normally free, with the exception of SecureCRT – more on these later. But in Packet Tracer you can just click the device and select the CLI tab. This is the equivalent of using a console connection in the simulation program.

If the device has been configured previously and you have network connectivity to the device, you would be able to use a remote connection method such as Telnet or SSH. The router could be in another country but as long as you and the device have an internet connection you can make configuration changes still.

The same terminal emulation programs used for console connections can be used to connect to a device via Telnet or SSH. If you have a choice between these two protocols you should always use SSH, this is because it uses encryption. Telnet is considered insecure because the packets can be captured, and everything can be read, including passwords. This will be demonstrated in Session 15.

I will SSH to my router using PuTTYY. To do this I select SSH on the radio buttons and then type the IP address of the device. When I click Open, we will be prompted for a username and password.

With any Cisco device, once you have a session open – either by console, Telnet or SSH – you will be presented with a prompt similar to this one. You will see the hostname, in this case Jason_Router. This is normally an identifiable name for the device, followed by the mode indicator. More on these modes in the next part of Session 10.