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 and rlogin connections to the router (“virtual terminals” or VTYs)
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