[arin-discuss] IPv6 End User Assignments

[michael.dillon at bt.com]

> What size of IPv6 subnet would you imagine an ADSL customer 
> (consumer, not business) would get from their ISP?  The NRPM 
> actually has nifty guidelines around subnet assignment here:
> 
> /64 when it is known that one and only one subnet is needed
> /56 for small sites, those expected to need only a few 
> subnets over the next 5 years. 
> /48 for larger sites 
> 
> I would assume that with the average Joe ADSL user, one 
> subnet is enough.  Whether or not an ISP would make that 
> assumption in their provisioning of the service might be 
> another question.

An ISP would be very stupid to make that assumption. Let's be
clear here. The English language definition of the word 
"assume" is to accept without verification or proof. In other
words, when you don't know something, then you might make
an assumption in the absence of knowledge, or not.

If the ISP does not "know" that there will only be one subnet
required, but just "assumes" that only one will be required,
then the ISP is not following the policy. In fact the policy 
is rather poorly written. It should start by saying that a
normal assignment is a /48. If the site is a small site expected
to need only a few subnets over the next 5 years, then a /56
assignment MAY be made. A /64 assignment should only be made
when it is known that one and only one subnet is required.

A good example of sites with a /64 assignment would be a remote
repeater station on top of a mountain or a fishing boat, or
a kiosk at a trade show.

> That said, I was a little surprised to see on the slashdot 
> article about the ARIN letter 
> (http://tech.slashdot.org/article.pl?sid=09/04/30/2051235&art_
> pos=2) that a comment came out suggesting every household 
> would have a /48 assigned to it.  What was more surprising is 
> that no comments surfaced to correct this claim.

That's because most ISPs will indeed be assigning a /48 to all
of their consumer customers. Only a few larger ISPs with very
large consumer subscriber bases, who are concerned with meeting
the HD ratio in 5 years when their /20 allocation runs out,
will be assigning consumers with a /56.

> My understanding of /48 is along with the NRPM: that /48 
> subnets are for "larger sites".  Not many consumers would use 
> much of their 65,536 /64 subnets in a /48 (at least in my estimation).

Your understanding is wrong probably because you are looking
in the wrong places. This is not a policy issue, it is 
related to the design of the IPv6 architecture. You will
find better information in RFCs and in books or presentations
about IPv6. The ARIN wiki <http://www.getipv6.info> has
many references to introductory materials as well as a page
on addressing based on the distilled knowledge of several
ISPs on the NANOG list.

> So, all this back to the original question:
> What kind of IPv6 subnet would YOU expect a North American 
> ISP to assign to their residential ADSL customer?

/48 as per standard.

--Michael Dillon