Concept builders are model-building inquiries and investigations leading to student-created explanations and animations of networking concepts, especially device algorithms and networking protocols. One intended use for Packet Tracer is for students to construct their own model or virtual networks, obtain access to important graphical representations of those networks, animate those networks by adding their own data packets, ask questions about those networks, and finally annotate and save their creations. The term "packet tracing" describes an animated movie mode where the learner can step through simulated networking events, one at a time, to investigate the microgenesis of complex networking phenomena normally occurring at rates of thousands and millions of events per second.
For example, a simple concept builder prompt might be "Illustrate the forwarding behavior of hubs" or "Demonstrate the filtering, forwarding, flooding, learning, and aging behavior of switches." Other prompts might include: "Build a PT network that compares and contrasts the behavior of hubs and switches," "How does switch behavior differ from router behavior?," and "Build a model demonstrating the behavior of ARP, ping, trace, CDP, RIP, or EIGRP." More complex modeling might be prompted by "Model a network that you use at home or at work," "Illustrate the behavior of ping with empty ARP tables on a LAN and across a WAN," "Demonstrate the building of RIP and EIGRP routing tables," or "Create a routing loop with static routes and show how the TTL field of an IP packet launched into this loop is decremented."
Many users may want to model networks they encounter at home or at work. Though this is often limited by the current device and protocol feature set of Packet Tracer, reasonably sophisticated models can be built. Model-building may be an effective way to learn many networking concepts, and often leads to more questions and research projects. Concept building problems are probably best written as blank or partially completed .pkt files. Given the open-ended inquiry nature of modeling, it is somewhat difficult to author an appropriate .pka file. Some instructors may want to give students a pre-existing topology via a .pkt file and focus students on different packet scenarios; other instructors may want to focus students on modeling a sequence of networks, from scratch, such as PC to PC, PC to hub, and PC to switch, and then on to more complex combinations of switches, routers, and clouds. Some instructors have students present their Packet Tracer models to the class.