Multihomed ASes

Definitions: AS with indegree > 1 in BGP AS graph is called multihomed
                        AS with outdegree > 0 in BGP AS graph is called transit

BGP gives only a lower bound on multi-homing, 
although a consistent one 
(26 vs. 39 tables differ by 0.3% in multi-homed ASes)

For Nov 01, 2001 RouteViews data, multihomed networks originated
76% of all prefixes 
74% of all more specific (subset) prefixes
includes transit & non-transit
multihomed nets originate a proper fraction of more specifics
Non-transit multihomed ASes contribute less prefixes than their fair share: 
                  Year    %AS     %prefixes
                  1999    43.65    27.46
                  2000    45.84    29.37
                  2001    48.75    29.74
Fraction of non-transit multihomed ASes grew in 1999-2001
Fraction of prefixes grew in 1999-2000, was constant in 2000-2001