5.2.4 This page will explain the features and functions of distribution layer switches.
Distribution layer switches are the aggregation points for multiple access layer switches. The switch must be able to accommodate the total amount of traffic from the access layer devices.
The distribution layer switch must have high performance. The distribution layer switch is a point at which a broadcast domain is delineated. The distribution layer combines VLAN traffic and is a focal point for policy decisions about traffic flow. For these reasons, distribution layer switches operate at both Layer 2 and Layer 3 of the OSI model. Switches in this layer are referred to as multilayer switches. These multilayer switches combine the functions of a router and a switch in one device. They are designed to switch traffic to gain higher performance than a standard router. If they do not have an associated router module, then an external router is used for the Layer 3 function.
The following Cisco switches are suitable for the distribution layer:
- Catalyst 2926G
- Catalyst 5000
family
- Catalyst 6000
family
Core layer overview
5.2.5 The core layer is a high-speed switching backbone. If they do not
have an associated router module, an external router is used for the Layer 3
function. This layer of the network design should not perform any packet manipulation.
Packet manipulation, such as access list filtering, would slow down the
switching of packets. A core infrastructure with redundant alternate paths
gives stability to the network in the event of a single device failure. 
The core can be designed to use Layer 2 or Layer 3 switching. ATM
or Ethernet switches can be used.The Interactive Media Activity will require students to identify the main functions of the access, distribution, and core layers.
The next page will discuss core layer switches.
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