Ubuntu – Bridge PPTP VPN with local network

Have you done setup of nat on your ubuntu box?

Here is example how to do it using iptables hope it will help you

#!/bin/sh

# iptables executable lives here
IPTABLES='/usr/sbin/iptables'
# renaming of our interfaces for better usability
# externail interface 
EXTIF='eth0'
# internal interface
INTIF='ppp0'
# flushing all of our rules
$IPTABLES -F
$IPTABLES -X
# switching on NAT 
# 192.168.1.0/24 - is an internal network behind our linux box
$IPTABLES -t nat -A POSTROUTING -s 192.168.1.0/24 -o $EXTIF -j MASQUERADE
$IPTABLES -A FORWARD -i $INTIF -o $EXTIF -m state --state NEW,ESTABLISHED -j ACCEPT

# optional tuning
# allow ssh connections to linux box
$IPTABLES -A INPUT --protocol tcp --dport 22 -j ACCEPT
# allow connections to http server on linux box
$IPTABLES -A INPUT --protocol tcp --dport 80 -j ACCEPT
# deny all other connections
$IPTABLES -A INPUT -i $EXTIF -m state --state NEW,INVALID -j DROP
$IPTABLES -A FORWARD -i $EXTIF -m state --state NEW,INVALID -j DROP

# port forwarding
# vnc
iptables -A PREROUTING -t nat -i $EXTIF -p tcp --dport 5900 -j DNAT --to 192.168.1.116:5900
iptables -A INPUT -p tcp -m state --state NEW --dport 5900 -i $EXTIF -j ACCEPT
# samba
iptables -A PREROUTING -t nat -i $EXTIF -p tcp --dport 139 -j DNAT --to 192.168.1.116:139
iptables -A INPUT -p tcp -m state --state NEW --dport 139 -i $EXTIF -j ACCEPT
iptables -A PREROUTING -t nat -i $EXTIF -p tcp --dport 445 -j DNAT --to 192.168.1.116:445
iptables -A INPUT -p tcp -m state --state NEW --dport 445 -i $EXTIF -j ACCEPT

I'm thinking that the LAN where the client is connecting from is using the same subnet as the LAN where the pptp server is, typically 192.168.1.0/24. If it is then that's the problem. The solution would be to use a different subnet on the client side or the server side.