Abstract: A method of constructing a forwarding database for a data communications network comprising a plurality of network components and supporting at least first and second topologies having one or more common network components is described. The forwarding database includes at least first and second database structures having records including forwarding information for data destined for related network components in the respective topologies. Each database structure has a plurality of elements including a pointer to one of a succeeding element or a record including said forwarding information. The method comprises the step, performed at a constructing network component of identifying a network component common to the first and second topologies for which a record exists in the second database structure. The method further comprises the step of including a pointer from the related element in the first database structure to a corresponding element or record in the second database structure.