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Objective 11: Telnet

You can also log in to a router using a virtual terminal connection. This is accomplished by telnetting from a computer or router on the network to the target router. You must know the IP address of one of the interfaces on the target router to log in using Telnet.

Telnetting is possible because of the Telnet protocol. Telnet is a TCP/IP Application layer protocol (the OSI model) that enables you to connect a local computer to a remote device, such as a router or other computer. The local computer becomes a virtual terminal that has access to applications and other resources on the remote device.

Software programs that support Telnet are often referred to as terminal emulation programs, meaning they enable the device to emulate or pretend that it is a dumb terminal connected directly to another device. Telnet is built into the Cisco IOS.

You can telnet to a router from a computer, switch, or router. In addition, when using Telnet on the router, you can telnet from the user or privileged modes. All you would need to know is the Telnet password for the remote router.

To telnet to a router from a router that provides a console connection, follow these steps:

  1. At the user mode prompt (or privileged mode prompt—more about the privileged mode in the next section), type telnet IP Address (where IP Address is the IP address of one of the target router's interfaces).

  2. Type the Virtual Terminal password at the Password prompt.

  3. Press Enter to enter the password.

You are then logged in to the remote router (see the following figure). You can now view settings related to the remote router. When you want to log off the remote router, you can type logout or exit and then press Enter.

Figure 3.13

After you are logged in to a router via a Telnet session, you can execute any of the CLI commands discussed in this chapter. However, to use commands available only in the privileged mode, such as show running config, you also must know the privileged password for the router to which you have telnetted.

One important point regarding Telnet on a router: You must make sure that the remote router has been configured for a virtual terminal password. Otherwise, you will not be able to telnet to the router.

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