PPTP/GRE Multi-forwarding NAT IPTables Example

Question

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?

Answer 1

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.

Answer 2

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.