On Tue, 21 Jul 2009 14:55:24 +0800 Kanagaraj <kanagaraj@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