Linux iptables open PPTP VPN dial-up failure solution

The company now uses iptables as the firewall in the LAN, the Internet is no problem. This time, because of the test, you need to connect PPTP VPN. The problem is, the VPN dial has failed and reported 619 errors. I have no problem with my cell phone or my home dialing.

Landing the router, the PPTP support all open to try again, the result is not.

Then find the reason for iptables, finally finally resolved.

1, add allow 1723 ports and GRE protocol in iptables.

2, loading iptables in several modules, IP_NAT_PPTP, IP_NAT_PROTO_GRE,IP_CONNTRACK_PPTP

Modprobe IP_NAT_PPTP
Modprobe Ip_nat_proto_gre
Modprobe IP_CONNTRACK_PPTP

To see if a module is loaded

root@ubuntu:/etc/iptables# lsmod |grep PPTP
NF_NAT_PPTP 2245 0
NF_CONNTRACK_PPTP 5549 1 NF_NAT_PPTP
Nf_conntrack_proto_gre 4734 1 NF_CONNTRACK_PPTP
Nf_nat_proto_gre 1719 1 NF_NAT_PPTP
Nf_nat 19286 3 Nf_nat_pptp,nf_nat_proto_gre,iptable_nat
Nf_conntrack 73326 7 nf_nat_pptp,nf_conntrack_pptp,nf_conntrack_proto_gre,xt_state,iptable_nat,nf_nat,nf_ Conntrack_ipv4

PPTP VPN dial is normal after successful loading and can be accessed normally