v6 subnet size for DSL & leased line customers

Mark Smith nanog at 85d5b20a518b8f6864949bd940457dc124746ddc.nosense.org
Fri Dec 28 03:52:37 UTC 2007

On Thu, 27 Dec 2007 18:08:10 -0800
"Scott Weeks" <surfer at mauigateway.com> wrote:

> First, thanks everyone for the discussion.  I learned more from this than a LOT of other discussions on IPv6.  I now have a plan and I didn't before...
> It looks to me that one really has to know his customer's needs to plan out the allocation of IPv6 space.  That leads me to believe that a /56 is going to work for everyone on this network because, at this time, only very, very few of our largest customers might possibly have a need for more than 256 /64 subnets.  In fact, almost all household DSL customers here only have one LAN and I could get away with /64s for them because they wouldn't know the difference.  But in an effort to simplify the lives of the network folks here I am thinking of a /56 for everyone and a /48 on request.

Out of curiosity, what in form would a request for a /48 need to be? A
checkbox on the application form, or some sort of written
justification? Remember that with an initial RIR allocation of a /32,
you've got 65K /48s ... so they're pretty cheap to give away.

> Now I just gotta wrap my brain around 4.7x10^21 addresses for each customer.  Absolutely staggering.

Ever calculated how many Ethernet nodes you can attach to a single LAN
with 2^46 unicast addresses? That's a staggering number too.


> scott
> --- randy at psg.com wrote:
> From: Randy Bush <randy at psg.com>
> To: Joel Jaeggli <joelja at bogus.com>
> CC: nanog at merit.edu
> Subject: Re: v6 subnet size for DSL & leased line customers
> Date: Thu, 27 Dec 2007 13:19:27 +0900
> >> vendors, like everyone else, will do what is in their best interests.
> >> as i am an operator, not a vendor, that is often not what is in my best
> >> interest, marketing literature aside.  i believe it benefits the ops
> >> community to be honest when the two do not seem to coincide.
> > If the ops community doesn't provide enough addresses and a way to use
> > them then the vendors will do the same thing they did in v4.
> i presume you mean nat v6/v6.  this would be a real mess and i don't
> think anyone is contending it is desirable.  but this discussion is
> ostensibly operators trying to understand what is actually appropriate
> and useful for a class of customers, i believe those of the consumer,
> soho, and similar scale.
> to summarize the positions i think i have heard
>   o one /64 subnet per device, but the proponent gave no estimate of the
>     number of devices
>   o /48
>   o /56
>   o /64
> the latter three all assuming that the allocation would be different if
> the site had actual need and justification.
> personally, i do not see an end site needing more than 256 subnets *by
> default*, though i can certainly believe a small minority of them need
> more and would use the escape clause.  so, if we, for the moment, stick
> to the one /64 per subnet religion, than a /56 seems sufficient for the
> default allocation.
> personally, i have a hard time thinking that any but a teensie minority,
> who can use the escape clause, need more than 256.  hence, i just don't
> buy the /48 position.
> personally, i agree that one subnet is likely to be insufficient in a
> large proportion of cases.  so keeping to the /64 per subnet religion, a
> /64 per site is insufficient for the default.
> still personally, i think the one /64 subnet per device is analogous to
> one receptacle per mains breaker, i.e. not sensible.
> > there are three legs to the tripod
> > 	network operator
> > 	user
> > 	equipment manufacturer
> > They have (or should have) a mutual interest in:
> > 	Transparent and automatic configuration of devices.
> as you have seen from chris's excellent post [0] on this one, one size
> does not fit all.  this is likely another worthwhile, but separate,
> discussion.
> > The assignment of globally routable addresses to internet
> > connected devices
> i suspect that there are folk out there who equate nat with security.  i
> suspect we both think them misguided.
> > The user having some control over what crosses the boundry
> > between their network and the operators.
> yup
> randy
> ---
> [0] - <http://www.merit.edu/mail.archives/nanog/msg04887.html>


        "Sheep are slow and tasty, and therefore must remain constantly
                                   - Bruce Schneier, "Beyond Fear"

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