In this paper we propose a new routing policy to route jobs to clusters in computational grids. This routing policy is based on index tables computed at each cluster. These tables can be computed off-line or on-line. Their computations use predictions about the average future behavior of the grid. We show how can be used in practice for task allocations in computational grids. We also report numerous simulations providing numerical evidence of the efficiency of our index routing policy compared with the classical brokers used in most production grids today. Ó 2007 Elsevier B.V. All rights reserved.