A campus LAN connects two or more buildings within a local geographic area using a high-bandwidth LAN media backbone. Usually the enterprise owns the medium (copper or fiber). High-speed switching devices minimize latency. In today's networks, Gigabit Ethernet campus backbones are the standard for new installations. In Figure 3-10, Layer 3 switches with Gigabit Ethernet media connect campus buildings.
Ensure that you implement a hierarchical composite design on the campus LAN and that you assign network layer addressing to control broadcasts on the networks. Each building should have addressing assigned in such a way as to maximize address summarization. Apply contiguous subnets to buildings at the bit boundary to apply summarization and ease the design. Campus networks can support high-bandwidth applications such as videoconferencing. Remember to use Layer 3 switches with high-switching capabilities in the campus-backbone design. In smaller installations, it might be desirable to collapse the building-distribution component into the campus backbone. An increasingly viable alternative is to provide building access and distribution on a single device selected from among the smaller Layer 3 switches now available.
Figure 3-10 Campus LAN
For large campus LANs, the Edge Distribution module provides additional security between the campus LAN and the Enterprise Edge (WAN, Internet, and VPNs). The edge distribution protects the campus from the following threats:
■ IP spoofing—The edge distribution switches protect the core from spoofing of IP addresses.
■ Unauthorized access—Controls access to the network core.
■ Network reconnaissance—Filtering of network discovery packets to prevent discovery from external networks.
■ Packet sniffers—The edge distribution separates the edge's broadcast domains from the campus, preventing possible network packet captures.
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