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Accessing a Cisco IOS Device

Console Access Method

There are several ways to access the Cisco CLI (Command-Line Interface) environment. The most common methods are

Console
Telnet or SHH
AUX port

Console

The console port is a management port that provides out-of-band access to a Cisco device. Out-of-band access refers to access through a dedicated management channel that is used for device maintenance purposes only. The advantage of using a console port is that the device is accessible even if no networking services have been configured, such as when performing an initial configuration of the networking device. When performing an initial configuration, a computer running terminal emulation software is connected to the console port of the device using a special cable. Configuration commands for setting up the switch or router can be entered on the connected computer.

The console port can also b used when the networking services have failed and remote access of the Cisco device is not possible. If this occurs, a connection to the console can enable a computer to determine the status of the device. By default, the console conveys the device startup, debugging, and error messages. After the network technician is connected to the device, he can perform any configuration commands necessary using the console session.

For many IOS devices, console access does not require any form of security, by default. However, the console should be configured with passwords to prevent unauthorized device access. In the event that a password is lost, there is a special set of procedures for bypassing the password and accessing the device. The device should also be located in a locked room or equipment rack to prevent unauthorized physical access.

Telnet, SSH, and AUX Access Methods

While a console connection provides a method of locally accessing the IOS CLI, there are methods for remotely accessing the CLI. This section introduces some of these methods.

Telnet

Telnet is a method for remotely establishing a CLI session of a device, through a virtual interface, over a network. Unlike the console connection, Telnet sessions require active networking services on the device. The network device must have a least one active interface configured with an Internet address, such a an IPv4 address. Cisco IOS devices include a Telnet server process that allows users to enter configuration commands from a Telnet client. In addition to supporting the Telnet server process, the Cisco IOS device also contains a Telnet client. This allows a network administrator to telnet from the Cisco device CLI to any other device that supports a Telnet server process.

SSH

The Secure Shell (SSH) protocol provides a remote login similar to Telnet, except that it uses more secure network services. SSH provides stronger password authentication than Telnet and uses encryption when transporting session data. This keeps the user ID, password, and the details of the management session private. As a best practice, use SSH instead of Telnet whenever possible.

Most versions of Cisco IOS include an SSH server. In some devices, this service is enabled by default. Other devices require the SSH server to be enables manually. IOS devices also include an SSH client that can be used to establish SSH sessions with other devices.

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