How to redirect all HTTP request to a local web server, supposing we don't have an internet connections
Exemple
I need to do this with iptables, and thank you guys for the help :)
This is an example taken from http://www.andybev.com/index.php/Using_iptables_and_PHP_to_create_a_captive_portal . This does exactly what you want:
IPTABLES=/sbin/iptables # Create internet chain # This is used to authenticate users who have already signed up $IPTABLES -N internet -t mangle # First send all traffic via newly created internet chain # At the prerouting NAT stage this will DNAT them to the local # webserver for them to signup if they aren't authorised # Packets for unauthorised users are marked for dropping later $IPTABLES -t mangle -A PREROUTING -j internet $IPTABLES -t mangle -A internet -j MARK --set-mark 99 # Redirects web requests from Unauthorised users to internet webserver $IPTABLES -t nat -A PREROUTING -m mark --mark 99 -p tcp --dport 80 -j DNAT --to-destination 192.168.1.1 # Now that we've got to the forward filter, drop all packets # marked 99 - these are unknown users. We can't drop them earlier # as there's no filter table $IPTABLES -t filter -A FORWARD -m mark --mark 99 -j DROP # Do the same for the INPUT chain to stop people accessing the web through Squid $IPTABLES -t filter -A INPUT -p tcp --dport 80 -j ACCEPT $IPTABLES -t filter -A INPUT -p udp --dport 53 -j ACCEPT $IPTABLES -t filter -A INPUT -m mark --mark 99 -j DROP