  We give lower bounds for the first non-zero Steklov eigenvalue on connected
graphs. These bounds depend on the extrinsic diameter of the boundary and not
on the diameter of the graph. We obtain a lower bound which is sharp when the
cardinal of the boundary is 2, and asymptotically sharp as the diameter of the
boundary tends to infinity in the other cases. We also investigate the case of
weigthed graphs and compare our result to the Cheeger inequality.
