Cisco Hierarchical Layer Model

The Hierarchical model helps a network administrator to break complex network problems into manageable problems. Cisco has divided its hierarchy into three levels or tiers. The three levels in Cisco Hierarchical model are

1. Core layer
2. Distribution layer
3. Access layer

Each layer devices have their own particular properties and responsibilities assigned to them. Consider OSI reference model. Tough it has seven layers protocols used in one layer are not used in other layers. The layering of devices helps an administrator to modify, add or remove the individual devices in the network very easily. Each layer may contain a router or switch or combination of both. Core layer:

This is the core of the network with the capabilities of handling large networks. Core layer transfers data at very high speeds. Tough the data is transmitted at high speeds; the reliability is maintained by core layer devices. The core layer devices are capable of handling high traffic. The main responsibilities of core layer devices are as listed below

1. Use of access lists
2. Maintain high-speed data transfers
3. Maintain routing traffic updates
4. Checking for any address translations
5. Providing security to data by encrypting the data

Distribution layer:

Distribution layer is often known as work group layer. Distribution layer acts as a dividing line between the core layer and access layer and acts as the communication link between these two layers. It isolates core layer from rest of network and acts as the mediator between the core layer and other network portions.  Distribution layer handles certain kinds of traffic by defining policies for the network. Apart from defining policies, the distribution layer also handles

1. Routing updates of the network
2. Enables routing between various VLAN’s
3. Defines boundary limits of broadcast and multicast domains
4. Provides security through firewalls and address translations.

Distribution layer also shares or redistributes the information between different routing domains when two different protocols are used over the network.

Access layer:

Access layer, also known as the desktop layer, contains switches and supplies traffic or data to the network devices like computer, printers, servers or IP phones. This layer is responsible for delivering data to the end devices. Access layer also provides security by preventing the entry of unwanted users over the network.

This is done by configuring access lists on network devices. Access layer creates separate collision domains. Access layer acts as the communication link between end devices and distribution layer devices.