What is the most standard subnet length on internet

Andy Davidson andy at nosignal.org
Fri Dec 19 02:45:36 CST 2008


On 19 Dec 2008, at 04:43, 정치영 wrote:

> It seems so simple. Currently annoucement of /24 seems to be okey,  
> most upstream providers accept this.
> However I wonder if there is any ground rule based on any standard  
> or official recommandation.

The only rule is "my network, my rules" ;-)

But if general rules did exist, they might say 1) not to announce  
smaller than a /24 to external parties without agreement, and 2) not  
to carve up registry assigned address blocks into individual  
announcements.

1 - You might announce your registry assigned block, AND deaggregated  
blocks to upstreams or peers for traffic engineering purposes, but you  
need to work closely with them to make sure that they don't filter the  
deaggs from your session, and also to make sure they don't onwardly  
announce the deaggs).

2 - The default free routing table is 270,000 entries large, and this  
is too big for lots of kit, so networks ARE FILTERING TODAY on  
registry boundaries.  If you don't understand the implications of this  
do not deaggregate the addresses that the registry assign you.

Good luck with your project.  Drop me a note offlist if you need  
specific advice.

Andy





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