OK, after two days of trying, here it goes (attention: always look outside the box, since my original problem was an XP box with a nonworking IPv6 stack... After switching to a laptop (also Win XP) it worked on the first try
)...This is what's been entered into a M0n0wall box:
1. In the SYSTEM->Advanced tick this box: Enable IPv6 support
2. After restart go to FIREWALL->IPv4 Rules and make sure that ICMP type Echo packets are allowed in and outbound on WAN.
Now you can register for a free HE TB tunnel. This is the data I got from the HE TB
(the tunnel's been erased... Just FYI
Server IPv4 address: 216.66.XX.XX
Server IPv6 address: 2001:470:1f0a:17c8::1/64
Client IPv4 address: 193.77.XX.XX
Client IPv6 address: 2001:470:1f0a:17c8::2/64
Routed /48: none
Routed /64: 2001:470:1f0b:17c8::/64
3. Go to FIREWALL->IPv6 Rules and make sure that ICMP (all types) packets are allowed in and outbound on WAN. This is good enough for testing, you should figure out for yourself which ICMP types are secure or not.
Still in FIREWALL->IPv6 Rules make sure that you allow all connections from Lan networks to any on LAN interface (since it's blocked by default, this is different as it was for IPv4!). Again, you might want to block some things here after testing is done...
4. Now we're getting down to bussiness. Go to INTERFACES->WAN->IPv6 configuration and select the Tunnel option in IPv6 mode menu. Paste the IP 2001:470:1f0a:17c8::2 into IPv6 address field and leave the mask at /64. That is all.
Then go to INTERFACES->LAN->IPv6 configuration IPv6 and select the static option in IPv6 mode menu. Paste the IP 2001:470:1f0b:17c8::1 into IPv6 address field and leave the mask at /64. Tick the box at Send IPv6 router advertisements.
M0n0 is ready now.
5. If you're gonna do testing on a XP box, go to command line and enter: ipv6 install.
Then check www.kame.net
and see the dancing turtle. Congrats, you've just seen how an IPv4/v6 dual stack works.