A diagnostic unit which detects instances of misconfiguration of a subscriber's PC is presented. Many problems experienced by PC subscribers attempting to access a network are related to misconfiguration of the subscriber's PC. The diagnostic unit is able to communicate with the subscriber's misconfigured PC through Fault Tolerant Protocol stacks. The diagnostic unit emulates services such as log-in, authentication, e-mail and the Internet to the subscriber. The diagnostic unit examines the traffic sent by the subscriber to detect instances of misconfiguration and reports the detected configuration of the subscriber's PC.