1.3 LAN Switching and the Hierarchical Model of Network Design
1.3.3 The distribution layer
The distribution layer of the network divides the access and core layers and helps to define and differentiate the core. This layer provides a boundary definition and is the place at which packet manipulation takes place. In the campus environment, the distribution layer can include several functions, such as the following:
  • Address or area aggregation
  • Departmental or workgroup access
  • Broadcast/multicast domain definition
  • VLAN routing
  • Any media transitions that need to occur
  • Security

In the noncampus environment, the distribution layer can be a redistribution point between routing domains or the demarcation between static and dynamic routing protocols. It can also be the point at which remote sites access the corporate network. The distribution layer can be summarized as the layer that provides policy-based connectivity.