Microsoft Call Back Configuration Protocol.
by Pedro Roque Marques
(updated by Paul Mackerras)
The CBCP is a method by which the Microsoft Windows NT Server may
implement additional security. It is possible to configure the server
in such a manner so as to require that the client systems which
connect with it are required that following a valid authentication to
leave a method by which the number may be returned call.
It is a requirement of servers to be so configured that the protocol be
So, this set of patches may be applied to the pppd process to enable
the cbcp client *only* portion of the specification. It is primarily
meant to permit connection with Windows NT Servers.
The ietf-working specification may be obtained from ftp.microsoft.com
in the developr/rfc directory.
The ietf task group has decided to recommend that the LCP sequence be
extended to permit the callback operation. For this reason, these
patches are not 'part' of pppd but are an adjunct to the code.
To enable CBCP support, all that is required is to uncomment the line
in Makefile.linux that sets CBCP=y and recompile pppd.
I use such script to make a callback:
pppd debug nodetach /dev/modem 115200 crtscts modem \
callback 222222 name NAME remotename SERVER \
connect 'chat -v "" atz OK atdt111111 CONNECT ""'
pppd debug /dev/modem 115200 crtscts modem \
name NAME remotename SERVER defaultroute \
connect 'chat -v RING ATA CONNECT "\c"'
First we invoke pppd with 'nodetach' option in order to not detach from
the controlling terminal and 'callback NUMBER' option, then wait for
1 second and invoke pppd again which waits for a callback (RING) and
then answers (ATA). Number 222222 is a callback number, i.e. server will
call us back at this number, while number 111111 is the number we are
You have to put in /etc/ppp/chap-secrets the following two lines:
NAME SERVER PASSWORD
SERVER NAME PASSWORD
You have to use your real login name, remote server name and password.