The multilayer approach to campus network design combines data link layer and multilayer switching to achieve robust, highly available campus networks. This section discusses factors to consider in a Campus LAN design.

Designing an Enterprise Campus

The Enterprise Campus network is the foundation for enabling business applications, enhancing productivity, and providing a multitude of services to end users. The following three characteristics should be considered when designing the campus network:

■ Network application characteristics: The organizational requirements, services, and applications place stringent requirements on a campus network solution—for example, in terms of bandwidth and delay.

■ Environmental characteristics: The network’s environment includes its geography and the transmission media used.

• The physical environment of the building or buildings influences the design, as do the number of, distribution of, and distance between the network nodes (including end users, hosts, and network devices). Other factors include space, power, and heating, ventilation, and air conditioning support for the network devices.
• Cabling is one of the biggest long-term investments in network deployment. Therefore, transmission media selection depends not only on the required bandwidth and distances, but also on the emerging technologies that might be deployed over the same infrastructure in the future.

■ Infrastructure device characteristics: The characteristics of the network devices selected influence the design (for example, they determine the network’s flexibility) and contribute to the overall delay. Trade-offs between data link layer switching—based on media access control (MAC) addresses and multilayer switching—based on network layer addresses, transport layer, and application awareness—need to be considered.

• High availability and high throughput are requirements that might require consideration throughout the infrastructure.
• Most Enterprise Campus designs use a combination of data link layer switching in the access layer and multilayer switching in the distribution and core layers.