This paper examines the extent of site multihoming in Finnish networks. Global route advertisements have been analyzed in general in a couple of studies, but this has not yielded sufficient information about the unclear cases of site multihoming. As these macroscopic approaches to analyze site multihoming have not been very successful, we analyze the questionable route advertisements in a "microscopic" fashion, checking them one by one. We provide description of the analysis methodology and define a taxonomy of the prefix advertisements and multihoming types.

The microscopic analysis leads us to conclude that more specific route advertisements through a different path than the aggregate do contain quite a few multihomed prefixes: a large number of the sites which have an AS number are multihomed, even though they would seem to be visible through one path only, while more specific routes advertised by other ISPs have a smaller chance (around 15%) of being multihomed. In addition, we confirm the obvious result that site multihoming with your own AS number and identical route advertisements through multiple providers is on the rise; some of these (at least 17%) do not have their own address space.