[Info-vax] implementing IPv6 on the internet

[Jan-Erik Soderholm]

Den 2016-09-23 kl. 23:22, skrev Dirk Munk:
> David Froble wrote:
>> 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.  I think I read once that it puts the
>> internal IP address in the packet.  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.
>>
>> Not real clean, but, wouldn't it work?
>
>
> I'll try to explain.
> suppose my pc wants to make a IPv4 connection with  microsoft.com, what
> happens?
> 1. It will do a nslookup for microsoft.com
> 2. it will get the IPv4 address X4 (and the IPv6 address X6) of microsoft.com
> 3. it will construct a packet with destination address X4, and sender
> address LAN4
> 4. It will send that packet to the router.
> 5. The router will exchange the LAN4 sending address by its own WAN4 address.
> 6. The packet will be send to microsoft.

> 7. return packets the other way around.

Point 7 is very oversimplificated... :-)

The return package arrives at the WAN address (there is only one,
don't really know what you mean with "WAN4"). The whole "thing" with
NAT is to decide where to sent the return package. The NAT tables
holds the originating internal IP address (and port no, since that
is also dynamicaly created by the web browser for each call).

So in your step 7 is where most of the "NAT magic" happens... :-)
It is not just "the other way around".

 > 5. The router will exchange the LAN4 sending address by its own WAN 
address and also storing the LAN4 address and LAN4 port number in the NAT 
tables and saves this as a WAN->LAN port number cross ref.

 > 6. The packet will be send to microsoft.

 > 7. Return packets arives to the WAN address of the router at the port 
number the router specifed in step 5 above. The router then knows that
any traffic comming into that specific port should be routed to the LAN4
IP addres and LAN4 port number stored in the NAT tables. That line in the
NAT tables is then cleared out.

>
> Let's see what happens with your idea.
> 1. It will do a nslookup for microsoft.com
> 2. it will get the IPv4 address X4 (and the IPv6 address X6) of microsoft.com
> 3. it will construct a packet with destination address X4, and sender
> address LAN4
> 4. It will send that packet to the router.
>
> And now we get a problem. How is the router suppose to know it has to build
> a new IPv6 packet with the same payload, but destination address X6, and
> sending address WAN6?