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Chapter 1: Campus Network Design

Excerpt from CCNP SWITCH 642-813 Cert Kit

By David Hucaby, Denise Donohue, and Sean Wilkins, Network World
January 29, 2010 08:30 PM ET

An enterprise campus generally refers to a network in a specific geographic location. It can be within one building or span multiple buildings near each other. A campus network also includes the Ethernet LAN portions of a network outside the data center. *Large enterprises* have multiple campuses connected by a WAN. Using models to describe the network architecture divides the campus into several internetworking functional areas, thus simplifying design, implementation, and troubleshooting.

The Hierarchical Design Model

Cisco has used the three-level Hierarchical Design Model for years. The hierarchical design model divides a network into three layers:

  • Access: Provides end-user access to the network. In the LAN, local devices such as phones and computers access the local network. In the WAN, remote users or sites access the corporate network.

    • High availability via hardware such as redundant power supplies and redundant supervisor engines. Software redundancy via access to redundant default gateways using a first hop redundancy protocol (FHRP).

    • Converged network support by providing access to IP phones, computers, and wireless access points. Provides QoS and multicast support.

    • Security through switching tools such as Dynamic ARP Inspection, DHCP snooping, BPDU Guard, port-security, and IP source guard. Controls network access.

  • Distribution: Aggregation point for access switches. Provides availability, QoS, fast path recovery, and load balancing.

    • High availability through redundant distribution layer switches providing dual paths to the access switches and to core switches. Use of FHRP protocols to ensure connectivity if one distribution switch is removed.

    • Routing policies applied, such as route selection, filtering, and summarization. Can be default gateway for access devices. QoS and security policies applied.

    • Segmentation and isolation of workgroups and workgroup problems from the core, typically using a combination of Layer 2 and Layer 3 switching.

  • Core: The backbone that provides a high-speed, Layer 3 path between distribution layers and other network segments. Provides reliability and scalability.

    • Reliability through redundant devices, device components, and paths.

    • Scalability through scalable routing protocols. Having a core layer in general aids network scalability by providing gigabit (and faster) connectivity, data and voice integration, and convergence of the LAN, WAN, and MAN.

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