[Info-vax] implementing IPv6 on the internet

[Jan-Erik Soderholm]

Den 2016-09-23 kl. 22:59, skrev David Froble:
> Dirk Munk wrote:
>> Richard Levitte wrote:
>>> Den fredag 23 september 2016 kl. 20:59:55 UTC+2 skrev Dirk Munk:
>>>> With "keep on dreaming" I was referring to your translation on the CE
>>>> router idea, IPv6 over the Internet, IPv4 at your home LAN.
>>>
>>> Oh, I'm sure someone will love NAT enough to do just that.
>>>
>>> Cheers,
>>> Richard ( #ishouldshutupnow )
>>>
>>
>> It's not that easy. It's not only the addresses, in many cases the way
>> the packets are set up has changed as well. Such a translation would be
>> quite a difficult undertaking, the CPU power of a simple CE router isn't
>> enough.
>>
>>
>
> Look, I'm not an expert at this stuff, but I have to ask, why is it so hard?
>
> Right now, NAT somehow figures which internal address to send a response
> coming back from the internet.

The request (such as to a web server) has a requester IP address and
a port number. The IP address is the public address of your NAT router
and the port number is used as an index into the NAT tables to look up
(by the router) what internal IP address to route the reply to.

For the external web server, it looks as it is the router that
does all the web calls. It doesn't see any differense between the
NAT router and some client doing the call directly. It just looks
as if the router had a lot of users surfing the net.


> I think I read once that it puts the internal IP address in the packet.

Maybe, but not used for the NAT routing. The NAT is internal to the
router and has nothing with the external access to do.

> Don't know much about that.  But if so,
> then at least returning packets via IPv6 could have inside the packet the
> IPv4 address for the internal system.
>
> As for connection attempts from outside, the sender would have to have
> knowledge of the internal address, and perhaps places that in the packet.
>

There also has to be a open port to connect to. If you have done
some "port forwarding" you have created a few such ports. If not,
there is only the ports that the are in the NAT tables available,
and they are highly dynamic.