[arin-ppml] Rationale for /22

Ted Mittelstaedt tedm at ipinc.net
Tue Jul 28 13:03:57 EDT 2009

Kevin Kargel wrote:
> Based on what everyone is saying about the /24 issue - and for the purpose
> of argument accepting that /24 will cause no problems - then why not take it
> a step further and remove any maximum length netmask restriction for a
> multi-homed entity with a single allocation.
> One entity with one allocation will generate one table entry regardless of
> what size it is, so why limit them to a /24.  I am sure there are entities
> out there who could operate just fine out of a /25 or even a /32, and so
> long as they are not creating gratuitous route table entries then we could
> be more efficient allowing them to only consume the space they need.

If you set the minimum size of a table entry to /25 instead of /24 then
you have now doubled the possible table entries.  It doesn't matter if 
the entries are gratuitous or not, the way subnet mathematics works, for
every drop in the bit boundary, from /25 to /26 to /27 and so on, you
double, quadruple, etc. the total possible route entries.

With the increase in router ram and router CPU speed over the years, 
some decrease in the minimum is warranted.  If we didn't have IPv6 
coming up - which will also double the number of advertisements once
everyone runs dual-stack - we could support an even further decrease
in the minimum.  But we can't yet support multiplying the number of
potential routing slots by 200 on the Internet.


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