HP MSM Wifi for Guests - limit access only to GW and DNS

Custom filters:
inbound: ether proto 0x888E or arp or (((udp (udp src port 53 and udp dst port 53)port 68 and udp dst port 67) or (udp src port 53 or udp dst port 53) or ether dst %b or ether dst %w or ether dst %g or multicast) and ((ether proto 0x8863 or ether proto 0x8864 or ip) and not (multicast and (udp port 137 or udp port 138 or udp port 139))))

outbound: (udp src port 53 or udp dst port 53) or ((ether proto 0x888E or arp or ((udp dst port 68 or ether src %b or ether src %w or ether src host %g or multicast) and ((ether proto 0x8863 or ether proto 0x8864 or ip) and not (multicast and (udp port 137 or udp port 138 or udp port 139 or udp dst port 3490))))) and (not ether dst 01:00:0c:cc:cc:cc))

Install DD-WRT on Buffalo WZR-600DHP2

1 Download the Official DD-WRT image from 
http://www.buffalotech.com/support-and-downloads/download/wzr600dhp2d-v24sp2-23709a.zip


2 login to http://192.168.11.1/cgi-bin/cgi?req=frm&frm=py-db/55debug.html
username: bufpy
password: otdpopypassword

Click on telnetd, click on Start

3 telnet 192.168.11.1 and type: "ubootenv set accept_open_rt_fmt 1"

4 point your browser to 
http://192.168.11.1/cgi-bin/cgi?req=frm&frm=py-db/firmup.html
5 upload the firmware you downloaded (and unziped) on step 1
6 wait.
7 wait.
8 WAIT I SAID!
9 wait some more time, then login to http://192.168.1.1/ admin:password 
- enjoy DD-WRT!

(thanks to Guilherme Garnier for correcting me at the last step)

Firmware 2.27 and higher have a slightly different procedure:

1 login to http://192.168.11.1/cgi-bin/cgi?req=frm&frm=py-db/55debug.html username "bufpy" password "otdpopypassword"
2 In a new tab, go to the normal web interface at http://192.168.11.1 (automatically logged in in debug mode)
3 Click on the new button "debug-disp"
4 Click on the (second to last) link "admin", then on the (first) link "name"
5 Click on the last link ending in firmup.html
6 In this interface, any ".bin" firmware (i.e. not in the typical Buffalo .zip package) can be uploaded without validation. It should also be possible to downgrade to an earlier Buffalo stock firmware on this page.