6.1 VLAN Issues
6.1.6 Distribution-layer topology
The distribution layer provides boundaries for different types of traffic such as broadcast and multicast traffic. This is also where inter-VLAN routing often occurs.

The distribution layer often consists of a combination of high-end switches and Route Processors. Because of its Layer 3 capabilities, the distribution layer becomes the demarcation between networks in the access layer and networks in the core. Each wiring-closet hub corresponds to a logical network or subnet that connects to the Route Processor, thus allowing the Route Processors in the distribution layer to provide broadcast control and segmentation as well as terminating collision domains.

The switch/Route Processor model is straightforward to configure and maintain because of its inherent modularity. Each Route Processor within the distribution layer is programmed with the same features and functionality. Common configuration elements can be copied across the layer, allowing for predictable behavior and ease of troubleshooting.