[arin-discuss] IPv6 End User Assignments

[Owen DeLong]

On May 6, 2009, at 7:43 AM, Matthew Wilder wrote:

> I have a question about subnet size for end user sites (and a few  
> thoughts as well).
>
> 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.  Either way,  
> I would bet that a /64 would suffice for 99% of users.
>
Were I running such a provider, I would assign a /64 with a /56  
automatic on request and a /48 with minimal justification.

> I can see value in assigning a /56 to every user so that they can  
> subnet to their hearts' content to save any trouble of renumbering  
> down the road, not that an average consumer would have a lot of  
> renumbering to do.
>
I figure the average consumer that didn't know they wanted more up  
front won't have too much trouble renumbering
that initial /64 if they have to.  Afterall, most of the renumbering  
can be done with a little global search and replace,
and the rest is probably not going to be too painful.  Especially if  
the /64 and a piece of the /56 can coexist for a
time which is perfectly feasible from a technical perspective.

> 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.
>
Please don't take the underinformed press (amateur press?) word for  
anything in this area.
RFC trumps press every day on the internet.  RIR policy also applies.  
The press is as likely
to get it wrong about IP as they do about Aviation, Meteorology, or  
any other detailed
technical issue.

> 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).
>
I have a /48 for my household and expect to use more than 256 subnets  
over time. The
bottom line is that in IPv6, you don't really think about how much of  
65,536 subnets
will they use, but, rather, is there a chance of using more than 256?  
OK... The next
boundary tends to default to /48.

> This got me to do some exploring.  I know that French telcos have  
> already got IPv6 available for their ADSL customers.  So with the  
> help of Google translation, I got the following page from a telco  
> called Nerim:
> http://translate.google.com/translate?hl=en&sl=fr&u=http://www.nerim.fr/ipv6&ei=iaEASrPINZritAPxjqX-BQ&sa=X&oi=translate&resnum=1&ct=result&prev=/search%3Fq%3Dnerim%2Bipv6%26hl%3Den%26rls%3Dcom.microsoft:en-US
>
> If you read near the bottom of the translated text, you will see  
> "For access, IPv6 allocation is a / 48..."  A /48 for a consumer?
>
That was the original intent of the IETF.  In the ARIN region, we've  
come to the conclusion that (in part because we probably
have more customers than the French ISPs) a /56 is a bit more rational  
in many cases.

> This made me curious to see what RIPE NCC says about end user  
> assignments.  They have similar language about the /64 being the  
> minimum, in the case that no subnetting is required.  They skip  
> over /56 (which makes me appreciate the ARIN policy) directly to / 
> 48.  They leave it to the LIR and ISP to determine what size of  
> assignments to make for end sites.
>
Indeed, the /56 was initially proposed in ARIN policy and has not  
gained wide acceptance yet in the rest of
the world.  I think that will likely change over time.  I think as /32  
holders start to gain more than 65,536
customers, you may well see them starting to try and figure out ways  
to not use up their next /32 so quickly.

> 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?
>
Default: /64
On request: /56
With justification: /48
With _ALOT_ of justification: up to a /32, possibly more.

Owen

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