If your neighbors are stealing your wireless internet access. You could encrypt it or alternately you could have fun. This will help battle wireless leeches out there. First, I'm doing all this in Linux (BackTrack 4).

Split the network

I'm starting here by splitting the network into two parts, the trusted half and the untrusted half. The trusted half has one netblock, the untrusted a different netblock. We use the DHCP server to identify mac addresses to give out the relevant addresses.

/etc/dhcpd.conf

ddns-updates off; ddns-update-style interim; authoritative;  shared-network local {          subnet *.*.*.* netmask 255.255.255.0 {                 range *.*.*.* *.*.*.*;                 option routers *.*.*.*;                 option subnet-mask 255.255.255.0;                 option domain-name "XXXXX";                 option domain-name-servers *.*.*.*;                 deny unknown-clients;                  host trusted1 {                         hardware ethernet *:*:*:*:*:*;                         fixed-address *.*.*.*;                 }   }          subnet 192.168.0.0 netmask 255.255.255.0 {                 range 192.168.0.2 192.168.0.10;                 option routers 192.168.0.1;                 option subnet-mask 255.255.255.0;                 option domain-name-servers 192.168.0.1;                 allow unknown-clients;          } }  

IPtables is Fun!

Suddenly everything is kittens! It's kitten net.

/sbin/iptables -A PREROUTING -s 192.168.0.0/255.255.255.0 -p tcp -j DNAT --to-destination 64.111.96.38 

For the uninitiated, this redirects all traffic to kittenwar.

For more fun, we set iptables to forward everything to a transparent squid proxy running on port 80 on the machine.

/sbin/iptables -A PREROUTING -s 192.168.0.0/255.255.255.0 -p tcp -m tcp --dport 80 -j DNAT --to-destination 192.168.0.1 

That machine runs squid with a trivial redirector that downloads images, uses mogrify to turn them upside down and serves them out of it's local webserver.

The redirection script

#!/usr/bin/perl $|=1; $count = 0; $pid = $$; while (<>) {         chomp $_;         if ($_ =~ /(.*\.jpg)/i) {                 $url = $1;                 system("/usr/bin/wget", "-q", "-O","/space/WebPages/images/$pid-$count.jpg", "$url");                 system("/usr/bin/mogrify", "-flip","/space/WebPages/images/$pid-$count.jpg");                 print "http://127.0.0.1/images/$pid-$count.jpg\n";         }         elsif ($_ =~ /(.*\.gif)/i) {                 $url = $1;                 system("/usr/bin/wget", "-q", "-O","/space/WebPages/images/$pid-$count.gif", "$url");                 system("/usr/bin/mogrify", "-flip","/space/WebPages/images/$pid-$count.gif");                 print "http://127.0.0.1/images/$pid-$count.gif\n";          }         else {                 print "$_\n";;         }         $count++; } 

Then the internet looks like this!