Troubleshooting activities include diagnosing, isolating, and fixing the simulated network from a previously bugged network file. Troubleshooting problems may range from simple (Ethernet speed and duplex mismatches, IP addresses on the wrong subnet, incorrect choices of cables, or missing clock settings on serial interfaces) to complex (improper VLSM schemes, incorrect routing updates, multiple interacting network faults). Both .pkt network files and .pka activity files may be effectively authored for troubleshooting-type problems. Precisely controlled troubleshooting situations may be authored as .pka files with the configurable components specified in the answer network (grading tree) of the Activity Wizard. For example, even very complex networks with thousands of potential configurable components can have a single bug introduced, and a .pka activity authored which requires the student to diagnose, isolate, and fix that one bug to complete the activity. The use of the .pka-file activity timer is particularly relevant for troubleshooting activities; for example, friendly competitions to see how efficiently students can repair a network.