Three types of topologies can be used in campus switched LAN design, as listed and described below:
- Scaled Switching
- Large Switching with Minimal Routing
- Distributed Routing and Switching
In a scaled switching LAN design, the entire LAN is comprised of only switches at all layers. No routers are used or integrated into the LAN. This design requires no knowledge of the addressing structure (since it is essentially a flat network), is low cost (from a monetary or financial point of view), and is very easy to manage.
However, the downside is that the entire campus LAN is still a single Broadcast domain. Even if Virtual Local Area Networks (VLANs) were used, users in one VLAN would not be able to communicate with users in another VLAN without the use of routers.
Large Switching with Minimal Routing
The large switching with minimal routing design deploys switching at the access, distribution, and core layers. At the distribution layer, routers are used to allow for inter-VLAN communication. In this topology, routing is used only in the distribution layer, and the access layer depends on bandwidth through the distribution layer in order to gain access to high-speed switching functionality in the core layer.
This design scales well when VLANs are designed so that the majority of resources are available in the VLAN. In other words, this design is suited for networks adhering to the legacy 80/20 rule. In modern-day client-server networks, this design would not be very scalable and therefore would not be recommended.
Distributed Routing and Switching
The distributed routing and switching design follows the LAN hierarchical network model both physically and logically, which allows this design to scale very well.
This design is optimized for networks that adhere to the 20/80 rule, which is the majority of modern-day client-server networks. This is the most common campus LAN design model in modern-day networks.