Two-Tier Campus LAN Design

The two-tier LAN design consists of two hierarchical layers:

• Access Layer

• Distribution Layer

Also called a 'Collapsed Core' design because it omits a layer that is found in the Three Tier design: the Core Layer.

Access Layer

• The layer that end hosts connect to (PCs, printers, cameras, etc).

• Typically Access Layer Switches have lots of ports for end hosts to connect to.

• QoS marking is typically done here.

• Security services like port security, DAI, etc, are typically performed here.

• Switchports might be PoE-enabled for wireless APs, IP phones, etc.

Distribution Layer

• Aggregates connections from the Access Layer Switches.

• Typically is the border between Layer 2 and Layer 3.

• Connects to services such as Internet, WAN, etc.

In a collapsed core design, the Distribution Layer is sometimes called the Core-Distribution Layer.

Connections between Distribution Switches are Layer 3. Routing information can be shared via OSPF (for example).

In large LAN networks with many Distribution Layer switches (for example in separate buildings), the number of connections required between Distribution Layer switches grows rapidly.

To help scale large LAN networks, you can add a Core Layer.

Cisco recommends adding a Core Layer if there are more than three Distribution Layers in a single location.