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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
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