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Re: IPv6 daydreams

  • From: Mark Smith
  • Date: Mon Oct 17 05:29:53 2005

Hi Randy,

On Sun, 16 Oct 2005 23:08:49 -1000
Randy Bush <[email protected]> wrote:

> > If we're going to do that, we may as well also start reclaiming
> > those 48 bit MAC addresses that come with ethernet cards. After
> > all, nobody would need anymore than say 12 to 13 bits to address
> > their LANs.
> so you think that layer-2 lans scale well above 12-13 bits?
> which ones in particular?

Maybe you've missed my point. Nobody (at least that I'm aware of)
_needs_ 48 bits of address space to address nodes their LANs. We didn't
get 48 bits because we needed them (although convenience is a need, if
it wasn't we'd still be hand winding our car engines to start them ). We
got them because it made doing other things much easier, such as (near)
guarantees of world wide unique NIC addresses, allowing "plug-and-play",
at least a decade before the term was invented.

I've read somewhere that the original ethernet address was only 16 bits
in size. So why was it expanded to 48 bits ? Obviously people in the 80s
weren't running LANs with 2^48 devices on them, just like they aren't

Why have people, who are unhappy about /64s for IPv6, been happy enough
to accept 48 bit addresses on their LANs for at least 15 years? Why
aren't people complaining today about the overheads of 48 bit MAC
addresses on their 1 or 10Gbps point-to-point links, when none of those
bits are actually necessary to identify "the other end" ? Maybe because
they have unconsciously got used to the convenience, and, if they've
thought about it, realise that the byte overhead/cost of that
convenience is not worth worrying about, because there are far higher
costs elsewhere in the network (including administration of it) that
could be reduced.



        The Internet's nature is peer to peer.