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)