I don't see a NAT rule for the GRE protocol: Iptables -A PREROUTING -t nat -p 47 -d xxx.xxx.xxx.xxx -j DNAT -to yyy.yyy.yyy.yyy That might be your problem, as said in the error message. -----Original Message----- From: netfilter-bounces@xxxxxxxxxxxxxxxxxxx [mailto:netfilter-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Tom Cruickshank Sent: 10 April 2005 00:27 To: netfilter@xxxxxxxxxxxxxxxxxxx Subject: question regarding pptp Hello, I have a question regarding pptp. I've read through many documentations and so far not sure what I've been doing wrong. I have a linux box which acts as a firewall. Port 1723 is ported to a windows RAS box inside the internal network. Here is what were my iptables rules. Iptables -A PREROUTING -t nat -p tcp -d xxx.xxx.xxx.xxx -dport 1723 -j DNAT -to yyy.yyy.yyy.yyy:1723 Iptables -append FORWARD -s yyy.yyy.yyy.0/24 -j ACCEPT Iptables -table nat -append POSTROUTING -out-interface ppp0 -j MASQUERADE Iptables -append FORWARD -p 47 -s yyy.yyy.yyy.0/24 -j ACCEPT xxx.xxx.xxx.xxx = external IP yyy.yyy.yyy.yyy = internal ip (ip for windows server) I was able to connect to the vpn server without any problems. Then the external IP changed. After changing the external IP in the iptables info, I keep getting A connection between the VPN server and the VPN client xxx.xxx.xxx.xxx has been established, but the VPN connection cannot be completed. The most common cause for this is that a firewall or router between the VPN server and the VPN client is not configured to allow Generic Routing Encapsulation (GRE) packets (protocol 47). Verify that the firewalls and routers between your VPN server and the Internet allow GRE packets. Make sure the firewalls and routers on the user's network are also configured to allow GRE packets. If the problem persists, have the user contact the Internet service provider (ISP) to determine whether the ISP might be blocking GRE packets. For more information, see Help and Support Center at As far as I can tell, the GRE packets SHOULD be going through. I've modified the Iptables to something like this without any success. iptables -A PREROUTING -t nat -p tcp -d xxx.xxx.xxx.xxx --dport 1723 -j DNAT --to yyy.yyy.yyy.yyy:1723 iptables -m state -A FORWARD -p tcp -s xxx.xxx.xxx.xxx/32 --state NEW -j ACCEPT iptables -m state -A FORWARD -p udp -s xxx.xxx.xxx.xxx/32 --state NEW -j ACCEPT iptables -m state -A FORWARD -p tcp -s yyy.yyy.yyy.0/24 --state NEW -j ACCEPT iptables -m state -A FORWARD -p udp -s yyy.yyy.yyy.0/24 --state NEW -j ACCEPT iptables -m state -A FORWARD -p 47 -s xxx.xxx.xxx.xxx/32 --state NEW -j ACCEPT iptables -m state -A FORWARD -p 47 -s yyy.yyy.yyy.0/24 --state NEW -j ACCEPT iptables -m state -A FORWARD -p 47 --state ESTABLISHED,RELATED -j ACCEPT iptables -m state -A FORWARD -p tcp --state ESTABLISHED,RELATED -j ACCEPT iptables -m state -A FORWARD -p udp --state ESTABLISHED,RELATED -j ACCEPT iptables -A input -p 47 -s yyy.yyy.yyy.0/24 -d xxx.xxx.xxx.xxx -j ACCEPT iptables --append FORWARD -p tcp --destination-port 1723 --jump ACCEPT iptables --table nat --append POSTROUTING --out-interface ppp0 -j MASQUERADE iptables --append FORWARD -s yyy.yyy.yyy.0/24 -j ACCEPT Would anyone have a clue what I might be doing wrong? Would appreciate any assistance. Thanks! Sincerely, Tom Cruickshank -- No virus found in this outgoing message. Checked by AVG Anti-Virus. Version: 7.0.308 / Virus Database: 266.9.5 - Release Date: 4/7/2005
