[ppml] /48 vs /32 micro allocations

Kevin Loch kloch at hotnic.net
Mon Mar 14 19:08:38 EST 2005

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

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.

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.

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

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

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?


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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