A data network has a number of inter-connected router devices forward received packets of data towards a destination node in accordance with a routing table associated with each router. A trust value is assigned to one or more other router devices, or links between router devices, in the network. A route metric is calculated in respect of one or more paths for forwarding on received data packets for onward transmission towards a specified destination. A next hop destination is selected for onward transmission of each such received packet to be forwarded on the basis of the calculated route metric for each applicable path. Each route metric is calculated in dependence upon the trust value assigned to one or more of the router or routers within each such path.