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| 1.1 |  | Overview of a Campus Network |
| 1.1.4 |  | The new 20/80 rule of network traffic |

In the networks of today, traffic patterns are moving toward what is now referred to as the 20/80 model as shown in Figure . In the 20/80 model, only 20 percent of traffic remains local to the workgroup LAN, and 80 percent of the traffic leaves the local network.

Two factors have contributed to these changing traffic patterns:

- The Internet – With web-based computing and Internet applications, a PC can be a tool for both publishing and accessing information. So information can now come from anywhere in the network, potentially creating massive amounts of traffic crossing subnet boundaries. Users hop transparently between servers across the enterprise by using hyperlinks, without having to worry about where the data is located.
- Server farms – The second factor leading to the decline of local-centric networks is the move toward server consolidation. Enterprises are deploying centralized server farms for the security, ease of management, and reduced cost of ownership. All traffic from the client subnets to these servers must travel across the campus backbone.

However, this change in traffic patterns requires the Layer 3 performance to approximate the Layer 2 performance. Because routing is a CPU-intensive process, this Layer 3 processing can create network bottlenecks. This is what drives the continued increase in requirements on campus networks.