3.3 How to Identify and Select Networking Capabilities
3.3.3 Three hierarchical WAN design layers
A hierarchical network design includes the following three layers:
  • The core layer provides optimal transport between sites 
  • The distribution layer, which provides policy-based connectivity
  • The access layer, which provides workgroup and user access to the network

The Figure shows a high-level view of the various aspects of a hierarchical network design.