A method is disclosed for generating a network topology representation based on inspection of application messages at a network device. According to one aspect, a network device receives a request packet, routes the packet to the destination, and extracts and stores correlation information from a copy of the request packet. When the network device receives a response packet, it examines the contents of a copy of the response packet using context-based correlation rules and matches the response packet with the appropriate stored request packet correlation information. It analyzes recorded correlation information to determine application-to-application mapping and calculate application response times. Another embodiment inserts custom headers that contain information used to match a response packet with a request packet into request packets.