From Cisco's website.
Advantages of connecting a modem on the console port:
Passwords can be recovered remotely.
It is a convenient method of attaching a second modem to a router without async ports.
Some routers (for example, Cisco 1600s) do not have AUX ports.
Disadvantages of connecting a modem on the console port:
The console port does not support RS232 modem control (data set ready/Data Carrier Detect (DSR/DCD), data terminal ready (DTR)). Therefore, when the EXEC session terminates (logout), the modem connection will not drop automatically; the user will need to manually disconnect the session.
More seriously, if the modem connection should drop, the EXEC session will not automatically reset. This can present a security hole, in that a subsequent call into that modem will be able to access the console without entering a password.
Unlike other async lines, the console port does not support hardware (Clear to Send/Ready to Send (CTS/RTS) flow control. It is recommended to use no flow control. If data overruns are encountered, however, software (XON/XOFF) flow control may be enabled.
The console ports on most systems only support speeds of up to 9600 bps.
The console port lacks reverse telnet capability. If the modem loses its stored initialization string, the only remedy is to physically disconnect the modem from the router and attach it to another device (such as an AUX port or a PC) to reinitialize. If a modem on an AUX port loses its initialization string, you can use reverse telnet remotely to correct the problem.
A console port cannot be used for dial-on-demand routing; it has no corresponding async interface.
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