This recipe has been tested to work on the Cisco PIX firewall. Modem was a USR 56k v.92 model 5686 modem. Plugged directly into the modem is a Cisco RJ45 to 25-pin serial adapter. This adapter is marked CAB-5MODEM on one side, 29-0881-01 on the other. A blue RJ45-RJ45 console cable was used between the adapter and the console port.
For security purposes, make sure that the console port is secured with a password or username/password and the timeout is set to something other than the default of 0. Otherwise, if you log into the port and fail to logout before disconnecting, it is possible for someone to dial into the router and take control of it without authentication.
I have not verified the instructions to connect a modem to the AUX port.
USR modem on console port
1) Set dip switches to 3,8 down, all others up
2) Connect modem to PC
3) Run hyperterminal and connect to modem at 9600 baud
4) Send init string: at&fs0=1&c1&h0&d2&r2&b1&m4&k0&n6&w
5) Set dip switches to 1,4,8 down, all others up
6) Connect modem to console port with appropriate cable
USR modem on Router AUX port
1) Set dip switches 3 and 8 down, all others up.
2) Connect modem to aux port using rolled (console) cable
and Cisco "modem" adapter.
3) Paste the following at an enable (#) prompt:
modemcap edit usrmodem misc &FS0=1&C1&D3&H1&R2&B1
line aux 0
transport input all
modem autoconfigure type usrmodem
NOTE: You might get errors on the "autoselect" lines.
4) Dial into modem. You should get a router prompt.
1) Type "show line" a couple of times and check
if speed of aux line is consistent. If it
changes, it is not autoconfiguring properly.
This means you do not have physical connectivity
to the modem. Power-cycle the modem, check the
cables, and then do "clear line aux 0".
2) If you get garbage when you dial into it, your
init string is bad. You may need a different
modemcap. Try this one:
modemcap edit usrmodem misc &F1S0=1
3) If you get nothing (not even garbage) when you
dial into it, reload the router.
4) If the modem does not answer when connected to
the router, but does answer when not connected,
try this modemcap:
modemcap edit usrmodem misc &FS0=1&C1&D3&H1&B1