line aux 0
Enters line configuration mode for the auxiliary (AUX) port, allowing configuration of console-like settings for remote out-of-band management via modem or terminal server.
line aux 0When to Use This Command
- Configuring a modem connected to the AUX port for dial-in remote management when the network is down.
- Setting login authentication and password for AUX access to provide out-of-band management.
- Adjusting line parameters such as baud rate, stop bits, or flow control for a terminal server connected to the AUX port.
- Enabling exec-timeout to automatically disconnect idle AUX sessions for security.
Command Examples
Basic AUX line configuration with password and exec-timeout
line aux 0
password cisco
login
exec-timeout 5 0Router(config-line)#
The command enters AUX line configuration mode. 'password cisco' sets the login password to 'cisco'. 'login' enables password authentication at login. 'exec-timeout 5 0' sets the EXEC timeout to 5 minutes and 0 seconds.
Configuring AUX line for modem dial-in with transport input
line aux 0
modem InOut
transport input all
speed 115200Router(config-line)#
'modem InOut' allows the modem to answer incoming calls and place outgoing calls. 'transport input all' permits all protocols (Telnet, SSH, etc.) over the line. 'speed 115200' sets the baud rate for the serial connection.
Understanding the Output
The 'line aux 0' command does not produce output; it changes the prompt to 'Router(config-line)#' indicating you are in line configuration mode. Subsequent configuration commands are applied to the AUX line. To verify settings, use 'show line aux 0' which displays line status, baud rate, modem state, and configured parameters. Key fields include 'Line' (line number), 'Baud rate' (speed), 'Modem' (modem state: ready, CTS, etc.), and 'Exec timeout' (idle timeout). A properly configured AUX line should show 'Modem' as 'ready' and 'Exec timeout' as set. Watch for 'Modem' showing 'no CTS' indicating a cable or modem issue.
CCNA Exam Tips
CCNA exam may ask which command enters AUX line configuration mode: 'line aux 0'.
Remember that AUX line is used for out-of-band management, typically via modem, and is configured similarly to console line.
Know that 'transport input' on AUX line can restrict protocols; 'transport input all' allows Telnet and SSH.
Be aware that 'exec-timeout' applies to all lines; setting it to 0 0 disables timeout (not recommended for security).
Common Mistakes
Mistake 1: Using 'line aux 0' in global config but forgetting to apply 'login' or 'password', leaving the line unsecured.
Mistake 2: Setting 'speed' too high for the connected modem or terminal server, causing connection issues.
Mistake 3: Confusing AUX line with console line; AUX is typically used for remote dial-in, not direct console access.
Related Commands
exec-timeout [min] [sec]
Sets the inactivity timeout for an EXEC session on a line, automatically logging out idle users to free up resources and enhance security.
show line
Displays line configuration and status information for console, auxiliary, and vty lines, used to verify line settings and monitor user connections.
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