Robert Elz writes:
> It was this kind of thing that led to 1918 addresses - the IETF
> invented (allocated) them precisely because of the problems that
> this (and other number "borrowing") caused.
But the real problem was renumbering. That
still hasn't gone away.
> | Assuming that you _never_ want to globally
> | advertise that prefix -- which is what site
> | locals are intended for -- does it actually
> | make any difference which prefix you choose?
>
> Yes. Because if you happen to choose a prefix that is someone
> else's globally allocated prefix, you can never talk to them.
> Or more likely, you find you have to renumber because you want
> to talk to them (if you're lucky, and never do, there's no issue).
Uh, except you can't talk to them anyway because
all you have is a non-globally-routable
address, right?
> If you're ever going to be in the position of having to renumber
> then the address you have isn't stable.
See above.
> | Why does IETF have to sanction one?
>
> One, as distinct from two or three or ... it doesn't. One as
> distinct from zero, so you know the address that you're going to
> be using will never be one that someone else uses (and you might
> need to use to communicate with them - their using it as a private
> address is harmless of course).
Except you can't communicate with them unless
you renumber or NAT anyway.
> | Why not just let people make their own decisions?
>
> They don't have enough information to make a good decision.
> Allocate several prefixes (like was done in 1918) and allow
> people to choose which they want to use if you like, that's
> fine - but they need to be prefixes reserved for the purpose.
Except neither does IETF, it seems. There's
no such thing as an long term stable
globally routable prefix. If you want a
globally routable address, you have to deal
with renumbering, regardless of whether you
got your "private" prefix from RFC 1918, or the
back of an old Ultrix manual.
> | BTW: isn't there already an implicit "site local"
> | address space for v6 with net 10 v4 mapped
> | address?
>
> If you mean the ::/80 address space (::/96 and ::FFFF:/96) then
[]
> If you mean 2002:0A00::/24 (which aren't usually called v4 mapped
[]
I'm not sure which one I mean, honestly, and am
too lazy to look it up. However, it seems that
if you have any v6 prefix which maps the
v4 space, you automatically get net 10's for
the bargain, and all of the hassles they
entail, including dealing with the v4 overlay
network routing. Keeping "private" addresses
as a v4 artifact -- which are still accessible
to v6 if you are so inclined -- may be a way
out of this...
Mike
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