I have set up a windows VPN server behind Linux - Ubuntu box that is working as firewall and proxy server. Now I want people from outside to be able to connect to the VPN server, but the connection is not being established and I get on the client an error 619. I have checked the problem on the internet and it seems a firewall issue. what should I do to make the connection established through the firewall? here is below the information about my setup Firewall-External-IF-IP: 172.16.1.100 Firewall-LAN-IF-IP: 192.168.1.1 VPN-Server-IP: 192.168.1.10 and below is my iptables file content: #Generated by iptables-save v1.4.12 on Thu May 29 12:40:18 2014 *filter :INPUT ACCEPT [162000:140437619] :FORWARD ACCEPT [23282:27196133] :OUTPUT ACCEPT [185778:143961739] :LOGGING - [0:0] -A INPUT -p gre -j ACCEPT -A INPUT -s 192.168.1.10/32 -p tcp -m tcp --sport 1723 -j ACCEPT -A INPUT -s 192.168.1.10/32 -p udp -m udp --sport 1723 -j ACCEPT -A FORWARD -s 192.168.1.0/24 -o EXT_IF -j ACCEPT -A FORWARD -s 192.168.1.0/24 -i EXT_IF -m state --state RELATED,ESTABLISHED -j ACCEPT -A FORWARD -d 192.168.1.10/32 -i EXT_IF -o INT_IF -p tcp -m tcp --dport 1723 -m state --state NEW,RELATED,ESTABLISHED -j ACCEPT -A FORWARD -s 192.168.1.10/32 -i INT_IF -o EXT_IF -p tcp -m tcp --sport 1723 -m state --state RELATED,ESTABLISHED -j ACCEPT -A FORWARD -d 192.168.1.10/32 -i EXT_IF -o INT_IF -p gre -m state --state NEW,RELATED,ESTABLISHED -j ACCEPT -A FORWARD -s 192.168.1.10/32 -i INT_IF -o EXT_IF -p gre -m state --state RELATED,ESTABLISHED -j ACCEPT -A OUTPUT -p gre -j ACCEPT -A OUTPUT -d 192.168.1.10/32 -p tcp -m tcp --dport 1723 -j ACCEPT -A OUTPUT -d 192.168.1.10/32 -p udp -m udp --dport 1723 -j ACCEPT COMMIT # Completed on Thu May 29 12:40:18 2014 # Generated by iptables-save v1.4.12 on Thu May 29 12:40:18 2014 *nat :PREROUTING ACCEPT [17865:1053739] :INPUT ACCEPT [5490:357281] :OUTPUT ACCEPT [3723:223677] :POSTROUTING ACCEPT [3726:223870] -A PREROUTING -p tcp -m tcp --dport 80 -j REDIRECT --to-ports 3128 -A PREROUTING -d 172.16.1.100/32 -i EXT_IF -p tcp -m tcp --dport 1723 -j DNAT --to-destination 192.168.1.10 -A PREROUTING -d 172.16.1.100/32 -i EXT_IF -p gre -j DNAT --to-destination 192.168.1.10 -A PREROUTING -i -h -A POSTROUTING -s 192.168.1.0/24 -o EXT_IF -j MASQUERADE COMMIT # Completed on Thu May 29 12:40:18 2014 # Generated by iptables-save v1.4.12 on Thu May 29 12:40:18 2014 *mangle :PREROUTING ACCEPT [22695965:17811993005] :INPUT ACCEPT [13818180:11522330171] :PREROUTING ACCEPT [17865:1053739] :INPUT ACCEPT [5490:357281] :OUTPUT ACCEPT [3723:223677] :POSTROUTING ACCEPT [3726:223870] -A PREROUTING -p tcp -m tcp --dport 80 -j REDIRECT --to-ports 3128 -A PREROUTING -d 172.16.1.100/32 -i EXT_IF -p tcp -m tcp --dport 1723 -j DNAT --to-destination 192.168.1.10 -A PREROUTING -d 172.16.1.100/32 -i EXT_IF -p gre -j DNAT --to-destination 192.168.1.10 -A PREROUTING -i -h -A POSTROUTING -s 192.168.1.0/24 -o EXT_IF -j MASQUERADE COMMIT # Completed on Thu May 29 12:40:18 2014 # Generated by iptables-save v1.4.12 on Thu May 29 12:40:18 2014 *mangle :PREROUTING ACCEPT [22695965:17811993005] :INPUT ACCEPT [13818180:11522330171] :FORWARD ACCEPT [8527694:6271564562] :OUTPUT ACCEPT [14748508:11899678536] :POSTROUTING ACCEPT [23271280:18170828012] COMMIT # Completed on Thu May 29 12:40:18 2014 hope that I find the solution here ....!! :(