[pptp-server] Trouble with MASQ, maybe

[Tim Brody]

I hope someone can help as this is beginning to go beyond annoying! :-)

I am trying to establish a pptp connection to my Linux box (running pptpd)
on an ADSL line from a Win2k box (both with real IPs).

I am receiving the error listed in the FAQ 7.3.5.:

Get "pptpd[24120]: GRE: read(fd=5,buffer=804d9c0,len=8196) from
	     PTY failed: status = -1 error = Input/output error"
	    "pptpd[24120]: CTRL: PTY read or GRE write failed (pty,gre)=(5,6)"
	    "pptpd[24120]: CTRL: Client 12.72.37.31 control connection finished"
	errors in your log file when the pptpd program is running on a machine
	behind a masq'ed firewall.

Although I am running MASQ for the machines sitting behind the Linux box, I
still get this error when I completely flush my firewall tables (iptables -t
nat -F PREROUTING etc.).

I can connect no problem from a machine connected to the Linux box across
ethernet (another Win2k box).

Linux box:

lo interface
eth0 192.168.0.* (to other MASQed LAN machines)
ppp0 215.* (ADSL connection to Internet)

Windows box:

lo interface
eth0 217.* (LAN connection to Internet, behind a firewall so I can't tunnel
_to_ this machine)

I've used tcpdump to watch vpn traffic and I can see GRE packets going to
and from the Linux box.

Any pointers greatly appreciated!
All the best,
Tim.