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Network Security Firewalls
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Re: PPTP

Subject: Re: PPTP
Date: Sun, 25 Sep 2005 09:27:21 +0200
Matt Mckinley wrote:

I have a linux IPtables firewall (latest version) that is in bridging mode.


There is another firewalling device behind it that is performing NAT.  When
a host behind that firewall connects to a PPTP server on a routable IP
address,
it appears that the IPTables linux box is breaking the connection.  When we
remove that device, the connection works fine.

Does anyone have any thoughts on what might cause this behavior?

Thanks!!

-Matt
 

as far as i remember PPTP protocol use a second GRE connections that is
started from the REMOTE PPTP Concentrator to the client requesting the
pptp connection. in fact on a PIX you have to add the "fixup command" to
deal with this issue.

check here
http://www.cisco.com/en/US/products/hw/vpndevc/ps2030/products_configuration_example09186a0080094a5a.shtml

i don't know if iptables has a conntrack module designed to deal with
this problem, if not you should need a 1-1 NAT for each client needing
the pptp connection.

bye

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