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The Hierarchical Internetworking Model, or the three-layer hierarchical model, is a network design approach that divides a network into three hierarchical layers to simplify designing, managing, and scaling networks. The model is primarily used in designing large-scale enterprise networks and has been popularized by Cisco Systems. The three layers in this model are:

#Core Layer: The core layer is the backbone of high-speed data transport between different network parts. It is designed to provide the fastest possible data transfer, focusing on efficient data forwarding with minimal processing overhead. Core layer devices, such as high-performance switches and routers, typically have minimal features enabled to reduce latency and maximize throughput.
#Distribution Layer: The distribution layer acts as a bridge between the core layer and the access layer, providing a range of services, such as routing, filtering, Quality of Service (QoS), and security. This layer aggregates data from multiple access layer devices and routes it to the appropriate core layer devices. The distribution layer enforces security policies and implements access controls to protect the network. Devices at this layer include switches and routers with more advanced features than those in the core layer.
#Access Layer: The access layer is the outermost layer of the network, where end-user devices, such as computers, printers, and other peripherals, connect to the network. This layer provides connectivity, network access, and basic security features, such as user authentication and access control. Devices at the access layer include switches, wireless access points, and sometimes routers.

The hierarchical internetworking model offers several benefits:

#Scalability: The hierarchical design allows for easier network expansion, as each layer can be independently scaled to accommodate growth.
#Manageability: Separating the network into distinct layers simplifies network management and troubleshooting, as issues can be isolated and addressed within the affected layer.
#Redundancy: The hierarchical model promotes the use of redundant links and devices, improving network reliability and fault tolerance.
#Performance: By separating different network functions into distinct layers, the hierarchical model can help optimize performance, as each layer can be fine-tuned for its specific tasks.

However, there are some challenges and drawbacks associated with the hierarchical internetworking model:

#Cost: Implementing a hierarchical network design can be more expensive than a flat network, as it may require additional hardware and more complex configurations.
#Complexity: Managing a hierarchical network can be more complex than managing a flat network due to the multiple layers and additional devices involved.

In summary, the hierarchical internetworking model is a network design approach that divides a network into three layers – core, distribution, and access – to simplify designing, managing, and scaling networks. This model offers benefits in terms of scalability, manageability, redundancy, and performance but can also introduce increased cost and complexity.



== See Also ==
*[[IT Strategy (Information Technology Strategy)]]
*[[IT Governance]]
*[[Enterprise Architecture]]
*[[Chief Information Officer (CIO)]]
*[[IT Sourcing (Information Technology Sourcing)]]
*[[IT Operations (Information Technology Operations)]]
*[[E-Strategy]]






== References ==
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