[AusNOG] My Predictions for the ISP Industry

[Geoff Huston]

On 16/03/2012, at 4:01 PM, Mattia Rossi wrote:

>> 
>>  >  This means that the
>>  >  CPE is creating a 6to4 prefix out of it's public facing IPv4 address,
>>  >  which is then used to distribute v6 addresses to all his IPv6 devices in
>>  >  the house.
>> 
>> More or less.  Or some other prefix.  But yes.
>> 
> 
> Some other prefix? E.g. fc00::/7 ?

no - it uses 2002:<public IPv4 address>::/48 as the router prefix and
performs a RA function for the interior network - don't forget that its IPv6
so there was a conscious effort to avoid address translation!

> 
>>  >  So far so good... but my question is: how do machines inside the house
>>  >  handle addresses of the 2002::/16 prefix?
>> 
>> When they're chatting among themselves, in all likelihood they
>> don't use 2002::/16 at all, and use link-local addresses instead.
>> 
>> (you see this on your LAN at home if you have any iOS devices
>> such as AppleTV's or WiFi associations with your iPhone:  Run
>> "ndp -a" on a Unix box and you'll see the link local addresses
>> for the iOS systems showing up as neighbors.  If your Unix box
>> happens to be a Mac, you'll even see them with .local mDNS names)
>> 
> 
> So there's some form of NAT happening (1:1 NAT)? Link local in the LAN, and if the destination is outside the LAN, the CPE keeps the 64 bit host part of the source address intact, rewrites the 64 bit prefix part to the 6to4 prefix, and off they go? Interesting...


not at all - they get addresses of the form <2002:<ipv4 external address>::<standard 64 bit interface ID>

Apple's airport's used to do this in an older verions (v2?), and I think there were
Linksys units with this function at some point, but I have forgotten the details.



Geoff