Cisco IOS in a Nutshell, 2nd Edition

Chapter 4. Line Commands

Cisco routers make a fairly basic distinction between the characteristics of a serial line (which you might want to think of as “physical” characteristics) and the characteristics of the protocols running over the line. The physical characteristics of a line are configured by the line command (and various commands that follow it) and include items such as parity and port speed. The high-level protocol characteristics are configured by the interface command (and the commands that follow it); these characteristics include IP addresses and other properties.

The line command can configure:

• The router’s console port (CTY)

• The router’s asynchronous ports (TTYs), used for dial-in and dial-out modem connections

• The router’s auxiliary port (AUX), used for backup modem connections

• Telnet, SSH, and rlogin connections to the router (“virtual terminals” or VTYs)

The line Command

The line command specifies which line or group of lines you want to configure by entering the line configuration mode. It doesn’t actually do the configuration; it is followed by other commands that set up the specific properties you want. Here’s the syntax of the line command:

line [aux | console | tty | vty] starting-line-number ending-line-number

The possible line types are aux, console, tty, and vty. These line types are discussed individually in this chapter. The following example shows how to use the line command to configure some properties of the router’s console interface:

Router>enable  
            Enter ...