PPTP problem with firewall

[Edoardo Mariconda]

Hi.

I have installed a firewall (IpCop 1.4.10 distribution) into
my office lan.
We have 4 vpn/pptp account on external server of our
customer for our remote assistance.
I have configured that account into my XP client and .....

- without firewall ----> all account works correctly
- with firewall -------> 3 account works correctly and 1
don't connect !!!!

Into log of my firewall I see that GRE packet from external
server with problem (which mount a CISCO PIX) are blocked
from my firewall, as it isn't able to nat (or conntrack)
that.

If I try from another office with another linux firewall
(supported by another people) all works correctly.
Maintainer of CISCO PIX of customer with problem, connect
from his office (with a linux firewall) and vpn connection
correctly works.

My configuration is (you can also view modules here:
http://www.ipcop.org/modules.php?op=modload&name=phpWiki&fil
e=index&pagename=IPCopSoftwares

Kernel: 2.4.31
Iptables: 1.2.11
ip_conntrack version 2.1
ip_conntrack_pptp version 1.9 loaded
ip_nat_pptp version 1.5 loaded

And I have also modules
ip_nat_proto_gre
ip_conntrack_proto_gre
---- (other vpn/pptp works correctly)

Note that I have also forwarded input 1723 connection on my
internal PPTP server (for come-in vpn connection) whitout
problem.

What kind of problem I have????

Thanks you.

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