While the hierarchical network design works well within the campus infrastructure, networks have expanded beyond these borders. As shown in the figure, networks have become more sophisticated and complex, with some requiring connections to dedicated data centers, often off-site. Branch sites often require connectivity to the campus backbones, and employees wanted to be able to work from home offices or other remote locations. As the complexity of the network increased to meet these demands, it became necessary to adjust the network design to one that uses a more modular approach.
A modular network design separates the network into various functional network modules, each targeting a specific place or purpose in the network. The modules represent areas that have different physical or logical connectivity. They designate where different functions occur in the network. Using a modular approach has several benefits, including:
- Failures that occur within a module can be isolated from the remainder of the network, providing for simpler problem detection and higher overall system availability.
- Network changes, upgrades, or the introduction of new services can be made in a controlled and staged fashion, allowing greater flexibility in the maintenance and operation of the campus network.
- When a specific module no longer has sufficient capacity or is missing a new function or service, it can be updated or replaced by another module that has the same structural role in the overall hierarchical design.
- Security can be implemented on a modular basis allowing for more granular security control.
The use of modules in network design enables flexibility and facilitates implementation and troubleshooting.