[arin-ppml] Rationale for /22

Chris Grundemann cgrundemann at gmail.com
Tue Jul 28 13:32:43 EDT 2009

On Tue, Jul 28, 2009 at 11:02, Kevin Kargel<kkargel at polartel.com> wrote:
>>   Obviously the primary reason for a limit is the accepted minimum routing
>> entry size of a /24.  Of course, you knew that.  So why ask the question?
> Perhaps it is time to examine the 'accepted minimum routing entry size'.  If
> it won't cause problems then why not extend the mask size?  Or are you
> saying that long mask route entries do in fact cause problems?

I don't think that anyone said lowering the minimum routing entry size
would not cause problems.  I am fairly certain that everyone agrees
that <rapid> route table expansion is a potential problem (primarily
caused by long route entries due to de-aggregation) and that we need
to continue to help ensure that the route table does not grow

The distinction that I (and I believe others) make is between the
source of a given Org's space and the addition of entries in the

AFAIK, there are no ISPs allowing customers to multihome with less
than a /24 currently but many who are allowing those /24s.  So if that
Org gets a /24 from ARIN or a /24 from it's ISP, there is the same 1
entry in the table.  And when that Org needs another /24 (and the ISP
did not reserve the adjacent one and the customer does not want to
renumber) and the ISP hands it another one, or ARIN hands it another
one, there are the same two entries.  There are two main differences
here though:
1) If ARIN policy requires that any Org with a /24 that wants more
space be required to return the original /24, then we end up with one
/23 instead of two /24s in the table.  This is more likely to happen
than most ISPs requiring renumbering because of all those pesky sales
teams and account managers...
2) If ARIN is giving space to a greater portion of all multihomers,
then ISPs have less excuses not to better aggregate their own space.
Load balancing should never require de-aggregation down to /24s.

Unless you stop allowing Orgs to multihome with less than a /22, there
will be longer entries in the table.  Perhaps we could actually slow
routing table growth by allowing them to get there space from ARIN
(since they will be getting and announcing it anyway)?  Or do you
think that getting space from ARIN will be so much easier than getting
it from an ISP that Orgs will flock to /24s and cause more growth in
the table than we currently see?


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Chris Grundemann

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