mco4s - 2005-05-06

I have got a poptop server running on a Redhat Ent 3.0 ES server with a iptables fw based on NAT. If I shutdown iptables PPTP runs perfect but when iptables is running it won't authenticate. The port 1723 is open in iptables and also GRE is allowed. The /var/log/messages gives the following loggings while trying to log in:

May 6 15:08:00 demolxsvr pppd[13754]: Using interface ppp0
May 6 15:08:00 demolxsvr pppd[13754]: Connect: ppp0 <--> /dev/pts/1
May 6 15:08:00 demolxsvr pptpd[13753]: GRE: Bad checksum from pppd.
May 6 15:08:00 demolxsvr /etc/hotplug/net.agent: assuming ppp0 is already up
May 6 15:08:30 demolxsvr pppd[13754]: LCP: timeout sending Config-Requests
May 6 15:08:30 demolxsvr pppd[13754]: Connection terminated.
May 6 15:08:30 demolxsvr pppd[13754]: Exit.
May 6 15:08:30 demolxsvr pptpd[13753]: GRE: read(fd=4,buffer=804e6e0,len=8196) from PTY failed: status = -1 error = Input/output error, usually caused by unexpected termination of pppd, check option syntax and pppd logs
May 6 15:08:30 demolxsvr pptpd[13753]: CTRL: PTY read or GRE write failed (pty,gre)=(4,5)
May 6 15:08:30 demolxsvr pptpd[13753]: CTRL: Client 212.125.138.38 control connection finished
May 6 15:08:30 demolxsvr /etc/hotplug/net.agent: NET unregister event not supported
May 6 15:09:49 demolxsvr smbd[13427]: [2005/05/06 15:09:49, 0] smbd/password.c:authorise_login(507)