You will need to allow gre traffic for pptp to work:
	sysctl net.inet.gre.allow=1

See /usr/local/share/doc/pptp/USING for an example configuration
specific to OpenBSD.

See http://www.counterpane.com/pptp-faq.html for a list of security flaws.
==========================================================================
ATTENTION:
Alcatel ADSL modems contain default logins with easily computed passwords.
See http://security.sdsc.edu/self-help/alcatel/ for more information.
==========================================================================
You may want to use TCP/IP packet filter rules to prevent unauthorized 
access to your modem (from internal net or spoofed/bounced TCP/IP packets).
