minimum IPv6 announcement size

Matt Palmer mpalmer at
Fri Sep 27 23:17:15 UTC 2013

On Fri, Sep 27, 2013 at 02:10:47AM -0400, Ryan McIntosh wrote:
> I don't respond to many of these threads but I have to say I've
> contested this one too only to have to beaten into my head that a /64
> is "appropriate".. it still hasn't stuck, but unfortunately rfc's for
> other protocols depend on the blocks to now be a /64..

I became a "convert" to the school of thought that hands out a /48 to every
end user when I realised that the current, *most* profligate addressing
scheme anyone's recommending involves essentially giving out an IPv6 /48 to
anyone who's currently getting an IPv4 /32 (eyeball SP end-users, and
dedicated server / VPS customers).  Even with this scheme, we have an
address space over eight *thousand* times greater than what we have now[1]. 
If I am the current IPv4 Internet, then we can have more IPv6 Internets than
there are people in the town I live in.

Once that sunk in, I realised that, practically speaking, we're solid.  Yes,
there have been a few "big" blocks like /20s handed out, but they're few and
far between.  I work for a comparatively *tiny* hosting company, and we've
got 3 IPv4 /20s, and yet the single IPv6 /32 we've got should more than do
us for a *very* long time to come[2].

I'm now firmly in the camp that the resource to be worrying about is routing
table slots, not address space exhaustion.

> It's a waste, even if we're "planning for the future", no one house
> needs a /64 sitting on their lan.. or at least none I can sensibly
> think of o_O.

I prefer to think of it as simply "enough address space I don't have to
worry about manual assignment", rather than "I'm 'wasting'
18446744073709551612 addresses".  Thinking of IPv6 as being a 48-bit or
64-bit address space that also has the added bonus of never having to worry
about host addressing makes things a lot more palatable.

- Matt

[1] And that's assuming that we only use 2000::/3 for this go around, which
is one of six /3 blocks that we have to play with.  If we completely fuck
this up, we've effectively got IPv's 7 through 11 to try different ideas
without having to change addressing formats.

[2] To be fair, we're using an IPv6 addressing scheme that involves a lot
more compaction than "/48s for everyone!", but even if we were handing out
/48s for every machine in our facilities (which we wouldn't need to do,
because plenty of customers have multiple machines, and thus would get a
single /48 for all their machines), we'd still not be running out any time
soon -- we've got ~65k IPv6 /48s, compared to ~12k IPv4 /32s, so yeah...

Generally the folk who love the environment in vague, frilly ways are at
odds with folk who love the environment next to the mashed potatoes.
		-- Anthony de Boer, in a place that does not exist

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