  We provide a both qualitative and quantitative comparison among different
approaches aimed to solve the problem of non-linear diffusive acceleration of
particles at shocks. In particular, we show that state-of-the-art models
(numerical, Monte Carlo and semi-analytical), even if based on different
physical assumptions and implementations, for typical environmental parameters
lead to very consistent results in terms of shock hydrodynamics, cosmic ray
spectrum and also escaping flux spectrum and anisotropy. Strong points and
limits of each approach are also discussed, as a function of the problem one
wants to study.
