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 a plurality of entries providing forwarding information for data destined for a related network component. The method comprises the step, performed at a constructing network component, of deriving topology dependent forwarding information for data destined for a network component. The method further comprises the step of including the topology dependent forwarding information at the related forwarding database entry.