The hierarchical internetworking model was introduced by Cisco in the late 1990s as an architectural concept for the design of networks involving large numbers of routers, switches, and other devices.
The three layers of the hierarchical model include:
The hierarchical internetworking model should not be confused with the OSI networking reference model. The two models address different concerns. The OSI model shows how different protocols encapsulate data within a single packet. The hierarchical model shows how different devices can connect and collaborate in an optimized manner. Within the hierarchical model, each device will pass numerous packets containing protocols at all seven layers of the OSI model. There is some intersection of the OSI model and the hierarchical model when it comes to the analysis of packet processing within the hierarchical model. For example, the access layer tends to limit header inspection to OSI layer two, whereas the distribution layer may inspect and process packet headers at OSI layer three or higher. Mainly, though, the coexistence of the hierarchical model and the OSI model show that the abstract idea of layers can be applied to a wide variety of concerns within the domain of distributed network architecture.