Explanation/Reference:
Section: Design Objectives Explanation
Explanation:
Most likely, hardware failures, physical link failures, and poor scalability can be mitigated by using a modular architecture. The modularity and hierarchy principles are complementary components of network architecture. The modularity principle is used to implement an amount of isolation among network components. This ensures that changes to any given component have little to no effect on the rest of the network. Thus hardware failures and physical link failures, which are detrimental to network stability and reliability, are less likely to cause system-wide issues. Modularity facilitates scalability because it allows changes or growth to occur without system-wide outages.
The hierarchy principle is the structured manner in which both the physical functions and the logical functions of the network are arranged. A typical hierarchical network consists of three layers: the core layer, the distribution layer, and the access layer. The modules between these layers are connected to each other in a fashion that facilitates high availability. However, each layer is responsible for specific network functions that are independent from the other layers.
The core layer provides fast transport services between buildings and the data center. The distribution layer provides link aggregation between layers. Because the distribution layer is the intermediary between the access layer and the campus core layer, the distribution layer is the ideal place to enforce security policies, provide load balancing, provide Quality of Service (QoS), and perform tasks that involve packet manipulation, such as routing. The access layer, which typically comprises Open Systems Interconnection (OSI) Layer 2 switches, serves as a media termination point for devices, such as servers and workstations.
Because access layer devices provide access to the network, the access layer is the ideal place to perform user authentication and to institute port security. High availability, broadcast suppression, and rate limiting are also characteristics of access layer devices.
Application failures and poor redundancy are less likely to be mitigated by using a modular architecture.
Poor redundancy and resiliency are more likely to be mitigated by a full-mesh topology. However, full-mesh topologies restrict scalability. Application failures can be mitigated by server redundancy.
Reference:
Cisco: Enterprise Campus 3.0 Architecture: Overview and Framework: ModularityCategory: Design Objectives