Upstreams blocking /24s? (was Re: How Not to Multihome)

Tue Oct 9 01:28:53 UTC 2007

On Mon, 8 Oct 2007, Jon Lewis wrote:

>>  adopted /24 as the cutoff point.  If you make the cutoff point smaller,
>>  what is the new point... /26?  /32?
>
> Anything longer than /24 is unlikely to propogate far on the internet. You 
> can all check your filters to see.  I just checked mine, and neither Level3 
> nor Time Warner has tried to send me anything longer than /24 in recent 
> history.  If they did, it'd show up as hits on a distribute-list deny rule.

I realize that - I was posing a rhetorical question to the previous 
poster :)

> This is actually in the ARIN "rules".  Multihoming is justification 
> (regardless of utilization) for one of the multihomed network's providers to 
> assign them a /24.

Been down that road a few times too, both as a provider and a customer.

jms