Re: Addressing plan exercise for our IPv6 course

[Fred Baker <fred () cisco com>]

I tend to think a /60 is a reasonable allocation for a residential user. In my home I have two subnets and will in time 
likely add two more: 
  - general network access
  - my office (required to be separate by Cisco Information Security policy)
  - (future) would likely want routable separate bandwidth for A/V at some point
  - (future) Smart Grid HAN will likely be its own subnet

If my wife went to work for a company with an infosec policy like Cisco's, that becomes a fifth subnet. Yes, 16 to 
choose from seems reasonable.

/56 seems appropriate to a small company, /48 for a larger company, and I could see a market for a /52. A company that 
needs more than a /48 is likely to also be using ULAs for some of its areas, which is an automatic extension, and could 
always justify another /48 (or one per continent) if it really needed them.

Could I do all this within a /64? Of course, with some thought, and by getting the Smart Grid and office prefixes from 
other sources (Cisco, my utility) and running them over a VPN (which I do anyway). The question is why I should have 
to. 

Why four bit boundaries? Because we're using hexadecimal, and each character identifies four bits. It makes tracking 
numbers simple - no "remember to count by N" as in IPv4. It's not magic, but to my small mind - and especially for of 
non-technical residential customers - it seems reasonable.

And yes, I think the logic behind a 48 bit MAC address is reasonable too.

On Jul 24, 2010, at 7:50 AM, Mark Smith wrote:

> On Fri, 23 Jul 2010 13:26:43 -0700
> Matthew Kaufman <matthew () matthew at> wrote:
>
> > sthaug () nethelp no wrote:
> > > > It is not about how many devices, it is about how many subnets, because you
> > > > may want to keep them isolated, for many reasons.
> > > >
> > > > It is not just about devices consuming lots of bandwidth, it is also about
> > > > many small sensors, actuators and so.
> > >
> > > I have no problems with giving the customer several subnets. /56 is
> > > just fine for that.
> > /56? How about /62? That certainly covers "several"... and if you're 
> > really worried they might have too many subnets for that to work, how 
> > about /60?
> > > I haven't seen any kind of realistic scenarios
> > > which require /48 for residential users *and* will actually use lots
> > > and lots of subnets - without requiring a similar amount of manual
> > > configuration on the part of the customer.
> > >
> > > So we end up with /56 for residential users.
> > Only because people think that the boundaries need to happen at 
> > easy-to-type points given the textual representation. /56 is still 
> > overkill for a house. And there's several billion houses in the world to 
> > hook up.
>
> So you're also strongly against 48 bit Ethernet MAC addresses? Dropping
> the two bits for group and local addresses, that's 70 368 744 177 664
> nodes per LAN. How ridiculous! What were those idiots+ thinking!
>
> "48-bit Absolute Internet and Ethernet Host Numbers", by Yogan K. Dalal,
> Robert S. Printis, *July 1981*
>
> http://ethernethistory.typepad.com/papers/HostNumbers.pdf
>
>
>
>
> + not actually idiots

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