  In this paper we calculate reaction and breakup cross sections for the two-
neutron halo nucleus of $^{11}$Li using the optical limit of Glauber theory.
Calculations are presented and compared to experimental data at 0.8 and 0.28
GeV/u on a series of targets. The $^{11}$Li nucleus is described as a
three-body system, a core plus two neutrons, with a phenomenological
neutron-core potential and a density dependent neutron-neutron interaction of
zero range. Three different wave functions are constructed which have different
$(2s_{1/2})^2$ and $(1p_{1/2})^2$ two-neutron components but correspond to the
same binding energy close to the experimental value. We show that the agreement
with all the experimental observables is achieved only if the 11Li wave
function contains about 30% of $(2s_{1/2})^2$ configuration.
