[arin-ppml] Rationale for /22

Leo Bicknell bicknell at ufp.org
Thu Jul 30 23:30:41 EDT 2009

In a message written on Thu, Jul 30, 2009 at 07:17:20PM -0500, David Farmer wrote:
> You are assuming that the number of multi-homed users will remain a 
> constant, if you allow a multi-home user with a PA based /24 from a provider 
> to switch to a PI based /24 from ARIN.  It is entirely possible that the 
> availability of PI /24s from ARIN for multi-homing could create an inducement 
> for more users to multi-home, just so they can get PI space.  

David summed it up well, however, a few notes.

If a network multihomes with a subnet of a PA block and someone
somewhere else in the routing table filters that route but not the
PA block, there is still full reachability.  If someone multihomes
with a PI block and that same person filters the same route, there
is no reachability.

Thus the size of the set of all routes is the same; but the size
of the filtered routes but still global reachability set is reduced.
There are a number of people trying to use the second set.

While the most traveled road is Multihome with PA, then Multihome
with PI, there are plenty of folks who single home with PA (no
global routing table slot) until they can qualify for an ARIN PI
block, then they multi-home.  There are users who go from nothing
to multi-homed; for instance startups who make sure they qualify
day 1 for a multi-homed prefix.  Presumably if the barrier was lower
more would do so.

I suspect many of the folks on this list would spend a lot more
effort trying to multi-home if they could get 1 /32 from ARIN for
$10 per year.  The number of cable modem and DSL customers asking
their providers for BGP would skyrocket.  It's not because those
folks are multi-homed with PA space today.

       Leo Bicknell - bicknell at ufp.org - CCIE 3440
        PGP keys at http://www.ufp.org/~bicknell/
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