[ppml] /48 vs /32 micro allocations

bmanning at vacation.karoshi.com bmanning at vacation.karoshi.com
Mon Mar 14 19:38:07 EST 2005

On Mon, Mar 14, 2005 at 07:08:38PM -0500, Kevin Loch wrote:
> Is there any benefit at all to allocating a /48 to name servers and
> exchange points instead of a /32?


> There is no shortage of /32's, with 536 million of them in 2000::/3.
> Even when you consider /29's being reserved for each ISP /32 there is
> no chance of running out of space by allocating /32's for any
> direct allocation, and "no chance" is understaded by several orders of
> magnitude.

	it does -seem- pretty large, doesn't it?

> Yet there may be a big problem with RIR allocated prefixes longer
> than /32.  Many operators are now only filtering prefixes longer than
> /48.  I suspect that the RIR allocated /48's are contributing to this,
> regardless of how trivial it is to filter around them.

	ISPs are free to filter on any boundar(y/ies) that they
	see fit to.  Many (most?) filter on published RIR allocation
	boundaries, some based on IETF recommendations, and SOME
	based on customer demand.

> An interesting example of this is /48 allocations for exchange points.
> These are explicitly not supposed to be routable yet they are in many
> networks.  RIR filter suggestions do not seem to matter, but allocation
> sizes do.

	Sort of.  No RIR delegation is explicitly routable. Routability
	is not an attribute of RIR delegations.  Routability is up to
	the respective ISP's.

> In other words, The minimum allocation from any RIR may eventually
> determine the Minimum Routable Unit (MRU) across the board.

	Not in my lifetime. :)

> Market forces, technology limitations and end site assignment sizes are
> also factors but there is a real risk that RIR allocations will result
> in a smaller MRU than these factors otherwise would.  I'm not saying
> that using /32's for special allocations will prevent a /48 MRU, but it
> is irresponsible to ignore the effects that these /48 allocations may
> have.

	There are other effects associated w/ large delegations that
	remain sparsely populated.

> So, to be on the safe and responsible side, should ARIN set a minimum
> allocation size of /32 for *any* direct allocation regardless of type?

	That would be bad - on many different levels.

> and,
> Should existing /48's be replaced with /32's to eliminate any
> RIR issued /48's in the global table?  For the RIR /48 delegates
> on this list, how do you feel about renumbering?
> Kevin Loch

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