2.3 3-tier
In 3-tier Cisco defines 3 layers of hierarchy, the core,distribution, and access each with specific function and it's referred to as a 3-tier network architecture.
Here is a description of each layer:
Access: Access layer controls user and workgroup access to the resources on the network. This layer usually incorporates Layer 2 switches and access points that provide connectivity between workstations and servers. You can manage access control and policy, create separate collision domains, and implement port security at this layer.
Distribution: Distribution layer serves as the communication point between the access layer and the core. Its primary functions are to provide routing, filtering, and WAN access and to determine how packets can access the core. This layer determines the fastest way that network service requests are accessed – for example, how a file request is forwarded to a server – and, if necessary, forwards the request to the core layer. This layer usually consists of routers and multilayer switches.
Core: Core layer also referred to as the network backbone, this layer is responsible for transporting large amounts of traffic quickly. The core layer provides inter-connectivity between distribution layer devices it usually consists of high speed devices, like high end routers and switches with redundant links.
