Switching Architectures Hierarchical Model – Distribution Layer

Hierarchical Model – Distribution Layer

The distribution layer is responsible for aggregating access layer switches,
and connecting the access layer to the core layer. Switches at the distribution
layer typically have the following characteristics:
• Layer-3 or multilayer forwarding
• Traffic filtering and QoS
• Scalable, redundant links to the core and access layers

Historically, the distribution layer was the Layer-3 boundary in a
hierarchical network design:
• The connection between access and distribution layers was Layer-2.
• The distribution switches are configured with VLAN SVIs.
• Hosts in the access layer use the SVIs as their default gateway.

This remains a common design today.
However, pushing Layer-3 to the access-layer has become increasingly
prevalent. VLAN SVIs are configured on the access layer switch, which
hosts will use as their default gateway.

A routed connection is then used between access and distribution layers,
further minimizing STP convergence issues and limiting broadcast traffic.

(Reference: CCNP Switch 642-813 Official Certification Guide by David Hucaby. Cisco Press)