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I followed this tutorial (http://elinux.org/RPI-Wireless-Hotspot) for an Wifi Hotspot in the guesthouse. This is working fine, but every device on the WiFi network can reach any LAN device in the LAN and vice versa. I don't want this (or at least block ARP spoofing) because there is some sensitive HTTP traffic (I can't use SSL).

Which iptables rules are needed to restrict the WiFi to only be used for "the internet"? I do login with SSH on the Rpi from the LAN.

  • Turn on WPA on the access point. Give passwords to guests. (You might still need to restrict traffic, but I am really sure you don't want to run a completely open access point, even if your guest house is a mile from anywhere.) – Bob Brown Oct 26 '14 at 21:33
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    It is public in the sense that guests can use it. It indeed has password protection and WPA on. – user1226868 Oct 26 '14 at 21:55
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After some debugging I found my problem It wasn't the firewall rules but the fact that the DHCP server for my LAN wasn't working (and thus creating an very strange scenario).

These are the rules I used (i flushed all previous iptables rules from the tutorial):

sudo iptables -P FORWARD DROP
sudo iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
sudo iptables -A FORWARD -i wlan0 -o eth0 -d 192.168.2.0/24 -j DROP
sudo iptables -A FORWARD -i wlan0 -o eth0 -j ACCEPT
sudo iptables -A FORWARD -i eth0 -o wlan0 -d 192.168.2.0/24 -j DROP
sudo iptables -A FORWARD -i eth0 -o wlan0 -j ACCEPT

And this results in:

Chain FORWARD (policy DROP 0 packets, 0 bytes)  pkts bytes target     prot opt in     out     source               destination
    0     0 DROP       all  --  wlan0  eth0    anywhere             192.168.2.0/24   192 11645 ACCEPT     all  --  wlan0  eth0    anywhere             anywhere
    0     0 DROP       all  --  eth0   wlan0   anywhere             192.168.2.0/24
    9  6286 ACCEPT     all  --  eth0   wlan0   anywhere             anywhere

What happens here, is that i refuse any traffic from my LAN (192.168.2.x) from going to the WLAN and vice versa. If the packets comply to this rule, I use NAT to transfer them to the gateway of the LAN and onto the internet.

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