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16. dialin: Configuration of a Dial-In Server

16.1 dialin: How can I enable others to login via ISDN?

The same way as via a normal serial port. Start a getty (mgetty from Gert Doering is highly recommended) on one of the ISDN devices with modem emulation (/dev/ttyI*). The entry in /etc/inittab looks like this: 

I0:56:respawn:/usr/local/sbin/mgetty ttyI0
I1:56:respawn:/usr/local/sbin/mgetty ttyI1
The init string needs to be entered in the mgetty.config, since mgetty needs to know which MSN or EAZ to listen to. For example: 
port ttyI0
modem-type data
speed 38400
init-chat "" ATZ OK AT&E0 OK AT&B512 OK
The example sets the EAZ (with 1TR6-ISDN) to 0. For Euro ISDN, the MSN (without area code) would be given instead of the 0 in "AT&E0". For X.75 the block size was set to 512 bytes. Alternatively you can enter the entire configuration onto a single line in /etc/inittab (here printed on two lines!): 
i0:45:respawn:/sbin/mgetty -D -m '"" ATZ OK AT&E0 OK AT&B512 OK'
-s 38400 ttyI0
The most elegant way is to use iprofd. This daemon takes advantage of the AT&W0 command in the i4l modem emulation. You start iprofd with a path as parameter, e.g. "iprofd /etc/i4lprofile" Then with minicom or another terminal program, open an ISDN tty device and enter the necessary AT commander by hand. When finished, enter the command AT&W0, then the kernel notifies iprofd to write the current configuration to the file. From now on it is enough to start iprofd in you isdn init script, and to initialize the appropriate ISDN tty devices with ATZ

16.2 dialin: How can I allow several people to call in to me at the same time?

You have to configure exactly as many gettys or network interfaces as the number of people allowed to call in at one time. These gettys or network interfaces can be set to the same MSN, since several people can be connected to a MSN at the same time (as long as there are B channels free). However, not more than one getty can be assigned to a single ttyI* device.

16.3 dialin: Someone would like to dial in to my mgetty with HDLC. Is ttyI1 correct, or do I have to start with ttyI0?

No, it doesn't matter. It also has nothing to do with the number of the B channel (0 or 1). You just have to activate HDLC in the init string (ATS14=3).

16.4 dialin: Is it possible with mgetty to automatically start pppd when LCP frames are received?

Yes, it is. This feature is called `AutoPPP'. See the configuration for mgetty.

16.5 dialin: How can I have (i)pppd check passwords from /etc/passwd instead of /etc/ppp/pap-secrets when someone dials in?

ipppd needs to be started with the options "login" and "auth". In /etc/ppp/pap-secrets, each user must have the following line to allow only certain users: 

login-name * "" *
To allow all users simply: 
* * "" *
The latter can also be achieved when the file pap-secrets does not exist.

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