Route table growth and hardware limits...talk to the filter

Tue Sep 11 20:08:03 UTC 2007

On Mon, 10 Sep 2007, Stephen Sprunk wrote:

>>> Sucks to be them.  If they do not have enough PA space to meet
>>> the RIR minima, the community has decided they're not "worthy"
>>> of a slot in the DFZ by denying them PI space.
>> 
>> Not true, there is an ARIN policy that allows you to get a /24 from
>> one of your providers even if you only need 1 IP address:
>
> If the PA /24 is under 199/8 or 204-207/8, then the filters being discussed 
> would allow their advertisement through, because ARIN's minimum allocation 
> for those blocks is /24.  In ARIN's 22 other /8s, the filters would not 
> because the minimum is /20 (or /22, for 208/8).

As long as enough NSPs don't filter on RIR minimums, there's still a 
pretty good chance that when a small PA multihomer's IP space provider's 
connection is down, traffic routed towards that provider will get rerouted 
to their other provider(s).

Breaking PA /24 multihoming would be unfortunate collateral damage.

Perhaps someone could use the data from the cidr-report and RIRs to create 
a precision targeted prefix-list intended just to block unnecessary more 
specifics rather than across the board on RIR minimums?

You could even do two different versions.  A loose version that just 
throws out covered subnets with same as-path and a BOFH version that 
throws out all apparently gratuitous subnetting smaller than RIR 
minimums, but not all smaller than RIR minimum routes.

I just wonder how huge the list would be and what the CPU and config size 
damage would be.

----------------------------------------------------------------------
  Jon Lewis                   |  I route
  Senior Network Engineer     |  therefore you are
  Atlantic Net                |
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