  We argue that salient experimental features of the magnetic excitations in
the SDW phase of iron-based superconductors can be understood within an
itinerant model. We identify a minimal itinerant model and use a multi-band RPA
treatment of the dynamical spin susceptibility. Weakly-damped spin-waves are
found near the ordering momentum and it is shown how they dissolve into the
particle-hole continuum. We show that ellipticity of the electron bands
accounts for the anisotropy of the spin waves along different crystallographic
directions and the gap at the momentum conjugated to the ordering one. We argue
that our theory agrees well with the neutron scattering data.
