Hi
As I wrote in the previous post it is theoretically possible to have a huge number of globally addressable devices sharing a single IPV4 Internet access point (your ADSL, Cable modem etc.). Practically there are some teething problems due to the fact that the NATs that we sit behind (Network Address Translation devices -
our routers or gateways allowing our local network to communicate with the Internet but at the same time be isolated from it) are often also not suitable for such operation. They understand UDP, TCP etc. but the IP 6in4 tunneling is something that they don't necessarily know, so often it gets blocked by the firewall. Further restrictions are that it may be possible to get it working with one device - in the extreme case by putting into the DMZ (de-militarized zone) but not allow multiple devices or multiple users to actually operate behind the NAT.
Experiments with the new IPV6 support in the uTasker development project have allowed this to be overcome by adding relay capability to the device in the DMZ. This device has the ability to recognised tunneled IPV6 traffic and relay it internally (after manipulation of the content) so that it is successfully delivered to the individual IPV6 device according to its global IPV6 address. This allows operation of multiple devices behind any NAT (single IPV4 address) even if it doesn't have any 6in4 tunneling compatibility, working with PCs or embedded devices.
The process is in fact quite simple since the device in the DMZ just needs to know the MAC address, IPV4 and IPV6 addresses of internal devices and can then adjust the received frames as follows (assuming that the address belongs to a particular PC):
1) MAC address is set to the PC's
2) IPV4 destination address is set to the PC's
3) The IPV4 check sum is re-calculated (due to the change in 2)
Furthermore it can also convert tunneled IPV6 frames to local RAW IPV6 frames (in fact even easier since it just needs to strip the IPV4 layer off and know the destination's MAC address).
The results of first tests were good, enabling a PC to communicate with IPV6 web sites even though the NAT used would normally not allow it. Reception traffic was being relayed by an embedded device using the uTasker IPV6 development stack with this new capability.
By the way, if you are wondering whether you can already work with IPV6 try this link:
http://www.kame.net/ If you see the dancing turtle you have managed to contact it using IPV6. If the turtle doesn't move then plain IPV4. Alternatively
http://www.apnic.net/ Here you will see the IP address that you reached the web site from. It may be your plain old IPV4 one (usually your routers) or else it will be an IPV6 one, with a little extra animation to celebrate this too.
For those of you who don't manage to connect via their own IPV6 address then don't worry because help is at hand. Watch this space for the appearance of a first uTasker tutorial explaining exactly what you need to do to get your first own several trillion free IPV6 addresses, configure your Windows PC (Linux and MAC also possible but you will need to check out some extra links for the details) and start browsing your first IPV6 web sites via any old router that you happen to be stuck behind. Then you will also be ready to add a few embedded devices to share this connection with your PCs - if you do have the physical space at least 16 million should be possible behind your single IPV4 address... but also no need to go overboard for first tests;-)
Regards
Mark
