In a computer network system that includes a multiplicity of nodes interconnected by a network of switches, wherein the nodes are linked to the network by respective data link adapters, a method for testing the adapters. One of the nodes is selected to serve as a destination node, and data are conveyed at a controlled rate from a plurality of the nodes, other than the destination node, through the respective adapters to the destination node. An error is detected in the data conveyed from one of the nodes so as to identify a fault in the adapter of that node.