Google is showing me some returns on PPTP/GRE NAT through iptables/netfilter that will allow multiple connections.

However, I am not finding an example of using this pptp helper module that allows for this. Anyone done this before?


This changed radically in kernel 2.6.14, and that accounts for the various random documentation examples you're finding (many with the pre-2.6.14 syntax). I don't have a machine handy to test on, but you should be fine with loading ip_conntrack_pptp and ip_nat_pptp to get PPTP connection tracking.

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  • Thanks this is a point in the right direction... will hold my accept to see if someone feels like spoonfeeding it to me :-) – Kyle Brandt Aug 5 '10 at 18:43
  • modprobe 'em and give it a go... >smile< – Evan Anderson Aug 5 '10 at 18:44
  • Venturing into WDS with AIK right now ... This all seems really cool ... as long as it works :-) Will give this a go later today hopefully. – Kyle Brandt Aug 5 '10 at 18:52
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    Ahh... automated Windows deployment... joy that it is. Good luck. – Evan Anderson Aug 5 '10 at 19:26
  • How can I add those modules in ubuntu 18.04 ? – Shyamkkhadka Jun 17 '19 at 8:19

I am assuming you are talking about being behind a NAT, and trying to have multiple users connect to a remote VPN server, then I just managed to fix this on DD-WRT v24-sp2 (04/16/10):

Apparently the kernel modules were missing which do the NAT translation for the GRE protocol - inserting them proved enough. I have added the following lines to the firewall script:

# Insert modules for PPTP over NAT:
insmod nf_nat_proto_gre
insmod nf_conntrack_proto_gre
insmod nf_conntrack_pptp
insmod nf_nat_pptp

The rest of iptables/netfilter is already set up correctly in DD-WRT apparently :)

If wanted I can dig up the rest of the NAT table entries relating to this.

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    Is that a 2.4 or 2.6 kernel underneath day DD-WRT build? (I'm looking at their web site and having a really hard time telling.) A 2.4 kernel will do this completely differently than a >= 2.6.14 kernel. – Evan Anderson Aug 9 '10 at 17:23
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    Uname -a tells me it is running 2.6.24 - indeed 2.4 would be quite different - apparently a lot has changed, amongst others the modules have been renamed to the nf_ netfilter prefix. – Tuinstoelen Aug 12 '10 at 7:23
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    You saved my day! My ISP provides internet access via PPTP channel, and the channel is kept up by home server. My job provides a VPN access to intranet via PPTP as well, and I couldn't connect to job PPTP VPN over my ISP PPTP. I googled for the solution several months, worked through my iptable rules uncountable times, and your solution made things work in the end! I added these modules to /etc/modprobe.d/pptp_nat.conf on my home server, and it works like a charm even after reboot! To complete the picture for guys who google around for the similar problem, my home server runs ArchLinux. – kstep Jan 15 '16 at 16:43
  • Like @kstep, this was working fine on my ArchLinux home server, but since I updated to kernel 4.7 last night, it just stopped working. – Stunts Aug 12 '16 at 9:40

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