On 11/20/2011 04:07 AM, Matthew Seaman wrote:
On 19/11/2011 18:47, 夜神 岩男 wrote:
Oh, and given you've got 64bits to play with, so long as your random
numbers are up to scratch no need to worry about collisions. You'ld
need to be assigning millions of addresses before you ran into that
problem.
Not to be an ass and this is likely a decade too early, but... this is
direct echoes of what I heard 20 years ago.
Does systematic thinking belong in /32+ IPv6 addressing or is it in fact
safe to just random it all away willy-nilly?
Look at http://en.wikipedia.org/wiki/Birthday_paradox
With 64bits of host address space in a typical IPv6 network, you would
need to be allocating 6.1 million addresses to have a 1 in a million
chance of a collision. You'ld need 5.1 billion addresses for a 1 in 2
chance of a collision. If you get a collision in a typical network of
maybe several hundred machines, then suspect your random number
generator before anything else.
I would appreciate the numbers more if we were talking in terms of
numbers of machines, as we were in the late 80's, but we're not. Now
everything has an address. With virtualization (which is a trend I tend
to buck, but is a prevalent force) it is currently normal for a single
machine to host tens or hundreds of IPs. With the mobile environment and
some concepts to simplify mobile-but-hubbed/homed devices even those
devices can inherit several IPs each. Is it not inconceivable that
complete ignorance of numeric paritioning could run us into weird places
quicker than we expect once again?
For example, a random assignment gives me something close to the < /8
space of the low end of my range and/or another pre-assigned address
region which was initially intended for a single machine -- until that
machine and its IP space became all cloudy like (the way 1st year
drop-out CIO's are getting sold on today). Now is this range enough, and
is the resolution overhead worth it in the future (10+ years of us
thinking IP ranges are freely available enough to just ranomd assignment
away) to push the next bajillion addresses to the same machine/cluster
(as it will no doubt evolve into at some point) to a totally separate
random remaining range once the available random addressing block is
used/randomed away?
The fact you cite the birthday paradox is interesting, as it predicts
that collisions are highly likely given the way we've grown to think
that every device should be multiply homed within a massively
multi-homed cluster and that IP assignments are totally costless today.
Or perhaps everyone is fatigued enough by the IP4 experience to just
wish this away.
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