[arin-discuss] IPv6 End User Assignments

[Garry Dolley]

On Sat, May 09, 2009 at 01:21:29PM +0100, michael.dillon at bt.com wrote:
> > > /48 as per standard.
> > 
> > What standard are you referring to?
> 
> None.
> "As per standard" is a colloquial way of saying "standard
> practice" which refers to the way that people have been
> doing things for the past few years. Of course it all 
> started with an RFC like 3177 which says:
> 
> -----quoted text------
> This document provides recommendations to the addressing registries
> (APNIC, ARIN and RIPE-NCC) on policies for assigning IPv6 address blocks
> to end sites. In particular, it recommends the assignment of 
> 
>    /48 in the general case, /64 when it is known that one and only one
>    subnet is needed and /128 when it is absolutely known that one and
>    only one device is connecting.
> 
> The original recommendations were made in an IAB/IESG statement mailed
> to the registries on September 1, 2000. This document refines the
> original recommendation and documents it for the historical record. 
> -----end quote-------
> 
> > From what I'm reading, a longer prefix, such as /56 is acceptable:
> 
> Yes it is acceptable but it is not standard practice. That change to
> policy was adopted to address an issue that a few very large ISPs
> have with the HD ratio.
> 
> The change was introduced with policy proposal 2005-8
> but please note the first sentence of the policy text
> of these guidelines:
> 
> The following guidelines may be useful 
> (but they are only guidelines):
> - /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
> 
> A large part of the rationale for this change to allow /56
> was in an earlier version of this Internet draft:
> <http://smakd.potaroo.net/ietf/idref/draft-narten-ipv6-3177bis-48boundar
> y/index.html>
> 
> There is a good section there explaining how /56 for
> residential users still maintains RFC 3177's goals.
> 
> > "Ideally, residential networks would be given an address range of a
> > /48 or /56 [RIPE_Nov07] such that multiple /64 subnets could 
> > be used within the residence." [1]
> > 
> > 1. RFC 5375 - IPv6 Unicast Address Assignment Considerations, 
> > Section 2.4
> 
> Like I said, /48 for residential networks is still
> standard practice.
> 
> I believe that the idea for a /56 first came from 
> Geoff Huston in this analysis:
> <http://www.potaroo.net/ispcol/2005-07/ipv6size.html>
> 
> If you have a network architecture which requires you
> to assign /48s to each POTENTIAL customer, then you
> are at risk of not qualifying for additional blocks
> because ARIN only counts ACTUAL customers. But, if
> you assign /56s to each POTENTIAL customer, you are
> almost certain to never need to go back to ARIN.
> Some cable providers need to assign a block to every
> residence that their cable goes past, which is why
> the policy was changed to allow for /56 assignments.
> 
> And, as the policy states, these are only guidelines.
> Some ISPs will need to assign a /47 or /46 per customer
> because their business model requires it. Maybe they
> specialise in connecting hotels who have a complex
> subnet plan to accomodate guest wifi subnets, room
> TV subnets, room telephony subnets, maid subnets per
> trolley, management subnets per section of each
> floor, banquet room subnets, conference subnets per
> kiosk, kitchen subnets, staff network subnets, bar
> wifi subnet, restaurant staff subnets, and lord knows
> what else. ARIN cannot dictate one size fits all,
> because increasingly, the ISP business is diversifying
> and there are all kinds of strange things out there.
> 
> --Michael Dillon

Yeah, I understand what you're saying now.  I've been reading RFC
3177 and 5375, and indeed /48 is the standard assignment.  I won't
plan to assign /64's to my customers b/c I can't be sure they are
not going to want to subnet, therefore I should give them the room
to do that with a /48.

To those on the list that mentioned they are defaulting to /64's, I
suggest you read RFC 3177 and 5375, and consider /48's.

-- 
Garry Dolley
ARP Networks, Inc. | http://www.arpnetworks.com | (818) 206-0181
Data center, VPS, and IP Transit solutions
Member Los Angeles County REACT, Unit 336 | WQGK336
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