What is the most standard subnet length on internet

John Kristoff jtk at cymru.com
Sun Jul 26 08:20:27 CDT 2009


On Tue, 21 Jul 2009 14:55:24 +0800
Kanagaraj <kanagaraj at globaltransit.net> wrote:

> Basically /24s are the longest prefix size accepted by providers
> unless you are dealing RTBH (triggered blackholing services). Another
> requirement to ensure acceptance of an IP block, especially smaller
> assignments are equivalent route objects matching it (in most cases
> your provider will do it on your behalf).

Randy Bush et al. have something interesting to say that challenges
this conventional wisdom or at least clarifies it.  See here for some
detail:

  <http://www.psg.com/~olaf/measurements/as3130/publications.html>

In part they show that the use of default routing might be much
more pervasive than people realize based on data plane measurements
they take (as opposed to control plane measurements).  They observe that
while a /25 does does not have the same reachability as a larger
prefix, it might still be reachable by a surprising number of ASes.

John




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