5.2 LAN Switches  
  5.2.3 Distribution layer overview  
The distribution layer of the network is between the access and core layers. It helps to define and separate the core. The purpose of this layer is to provide a boundary definition in which packet manipulation can take place. Networks are segmented into broadcast domains by this layer. Policies can be applied and access control lists can filter packets. The distribution layer isolates network problems to the workgroups in which they occur. The distribution layer also prevents these problems from affecting the core layer. Switches in this layer operate at Layer 2 and Layer 3. In a switched network, the distribution layer includes several functions such as the following:
  • Aggregation of the wiring closet connections
  • Broadcast/multicast domain definition
  • Virtual LAN (VLAN) routing
  • Any media transitions that need to occur
  • Security

 

Web Links

Understanding Network Models – The Cisco Network Design Model

http://www.2000trainers.com/article.
aspx?articleID=56&page=1