Assigning IPv6 /48's to CPE's?

michael.dillon at michael.dillon at
Mon Dec 31 09:30:54 UTC 2007

> I believe someone posted the ARIN recommendation that 
> carriers assign out /64's and /56's, and in a few limited cases, /48. 
> I can understand corporations getting more than a /64 for 
> their needs, but certainly this does not mean residential ISP 
> subscribers, right?

Then you misunderstand ARIN's recommendations. The basic IPv6
assignment size is /48. ARIN recommends assigning a /48 to all
customers who cannot be guaranteed to only need a single subnet.
It is possible that some ISPs offer a specialty service, say
IPv6 connectivity to CCTV cameras, which only needs a single
/64 but general purpose ISPs providing general Internet accesss
to consumers and businesses should assign a /48. Some ISPs have
very large numbers of consumer customers and feel that the large
number of /48s they will need may be excessive, therefore ARIN
also recommends that in the case of providing connectivity to
a private residence, a /56 may be used. In order to support the
use of a /56 assignment in this situation, ARIN has adjusted some
parts of their policy to do with counting, so that they measure
/56 assinments rather than /48 assignments. But a /48 assignment
is still fully justified.

> There are also serious privacy concerns with having a MAC 
> address within an IP address. Aside from opening the doors to 
> websites to share information on specific users, lack of NAT 
> also means the information they have is more detailed in 
> households where separate residents use different computers.

Aside from the fact that you can change your MAC at will, 
there is no need to use the MAC as the IPv6 node address.
You can change your IPv6 node address every day if you wish.
> I can become an IPv4 stranger to websites once a week by 
> deleting cookies, IPv6 means they can profile exactly what I 
> do over periods of years from work, home, starbucks, it 
> doesn't matter. I don't see NAT going away any time soon. 

This only works if your ISP assigns your IP address dynamically
and your lease times out without renewal, i.e. you power down
your gateway device long enough to get a new IP address. Same
applies to IPv6.

--Michael Dillon

More information about the NANOG mailing list