Technical data

How to set up a dial-in callback server

A dial-in callback server allows you to gain access to your system using the callback procedure.

The callback procedure allows you to establish the connection, invoke the authentication procedure and provide

phone number where the dial-in server will call you back.

The description for setting up a dial-in callback server is based on How to set up a dial-in server on page 79

and provides only changes.

General Description

The mgetty utility is responsible for the initialization of the TTY interface and for the answering of the incoming

calls. Once the call establishment is complete, mgetty will start the modified pppd utility pppd.callback. The

pppd.callback will establish the PPP link, invoke the authentication procedure and obtain callback parameters.

Finally, pppd.callback will disconnect the link and execute the user-provided application (script) that will issue

the call back.

Setting up a dial-in callback server

1. Set up the dial-in server using How to set up a dial-in server on page 79. Finally, follow the described

procedure below to configure a dial-in callback server.

2. Install the changed ppp.callback ppp application in the /usr/sbin directory.

3. Change the context of the /etc/mgetty+sendfax/login.config file as follows (it uses now the changed ppp

application ppp.callback):

# Automatic PPP startup on receipt of LCP configure request (AutoPPP).

# mgetty has to be compiled with "-DAUTO_PPP" for this to work.

/AutoPPP/ - a_ppp /usr/sbin/pppd modem

# Disable login sessions

* - - /bin/false @

4. Change the context of the /etc/ppp/options file as follows:

# Common options for TTY interfaces

# Debug

#debug 9

#kdebug 9

# Allow callback operation and set-up callback script

callback 211

callbackscript /etc/ppp/callback.sh

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