  We present here a study of the clustering and cycles present in the graph of
Internet at the Autonomous Systems level. Even if the whole structure is
changing with time, we present some evidence that the statistical distributions
of cycles of order 3,4,5 remain stable during the evolution. This could suggest
that cycles are among the characteristic motifs of the Internet. Furthermore,
we compare data with the results obtained for growing network models aimed to
reproduce the Internet evolution. Namely the fitness model and the Generalized
Network Growth model. We are able to find some qualitative agreement with the
experimental situation even if the actual number of loops seems to be larger in
the data than in any proposed growing network models. The task to capture this
feature of the Internet represent one of the challenges in the future Internet
modeling.
