Chapter 1: Campus Network Design

Excerpt from CCNP SWITCH 642-813 Cert Kit

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Excerpt from CCNP SWITCH 642-813 Cert Kit: Video, Flash Card, and Quick Reference Preparation Package.

By David Hucaby, Denise Donohue, and Sean Wilkins

Published by Cisco Press

ISBN-10: 1-58720-318-9

ISBN-13: 978-1-58720-318-3

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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.

    • No policies such as ACLs or filters that would slow traffic down.

A set of distribution devices and their accompanying access layer switches are called a switch block.

Core Layer

Is a core layer always needed? Without a core layer, the distribution switches must be fully meshed. This becomes more of a problem as a campus network grows larger. A general rule is to add a core when connecting three or more buildings or four or more pairs of building distribution switches. Some benefits of a campus core are:

  • Adds a hierarchy to distribution switch connectivity

  • Simplifies cabling because a full-mesh between distribution switches is not required

  • Reduces routing complexity by summarizing distribution networks

Small Campus Design

In a small campus, the core and distribution can be combined into one layer. Small is defined as fewer than 200 end devices. In very small networks, one multilayer switch might provide the functions of all three layers. Figure 1-1 shows a sample small network with a collapsed core.

Figure 1-1

Small Campus Network

Medium Campus Design

A medium-sized campus, defined as one with between 200 and 1000 end devices, is more likely to have several distribution switches and thus require a core layer. Each building or floor is a campus block with access switches uplinked to redundant multilayer distribution switches. These are then uplinked to redundant core switches, as shown in Figure 1-2.

Data Center Design

The core layer connects end users to the data center devices. The data center segment of a campus can vary in size from few servers connected to the same switch as users in a small campus, to a separate network with its own three-layer design in a large enterprise. The three layers of a data center model are slightly different:

  • Core layer: Connects to the campus core. Provides fast switching for traffic into and out of the data center.

  • Aggregation layer: Provides services such as server load balancing, content switching, SSL off-load, and security through firewalls and IPS.

  • Access layer: Provides access to the network for servers and storage units. Can be either Layer 2 or Layer 3 switches.

Figure 1-2

Medium-Sized Campus Network

Network Traffic Flow

The need for a core layer and the devices chosen for the core also depend on the type of network traffic and traffic flow patterns. Modern converged networks include different traffic types, each with unique requirements for security, QoS, transmission capacity, and delay. These include

  • IP telephony signaling and media

  • Core Application traffic, such as Enterprise Resource Programming (ERP), Customer Relationship Management (CRM)

  • Multicast multimedia

  • Network management

  • Application data traffic, such as web pages, email, file transfer, and database transactions

  • Scavenger class traffic that requires less-than-best-effort treatment

The different types of applications also have different traffic flow patterns. These might include

  • Peer-to-Peer applications such as IP phone calls, video conferencing, file sharing, and instant messaging provides real-time interaction. It might not traverse the core at all, if the users are local to each other. Their network requirements vary, with voice having strict jitter needs and video conferencing using high bandwidth.

  • Client-Server applications require access to servers such as email, file storage, and database servers. These servers are typically centralized in a data center, and users require fast, reliable access to them. Server farm access must also be securely controlled to deny unauthorized users.

  • Client-Enterprise Edge applications are located on servers at the WAN edge, reachable from outside the company. These can include email and web servers, or e-commerce servers, for example. Access to these servers must be secure and highly available.

Service-Oriented Network Architecture

Service-Oriented Network Architecture (SONA) attempts to provide a design framework for a network that can deliver the services and applications businesses need. It acknowledges that the network connects all components of the business and is critical to them. The SONA model integrates network and application functionality cooperatively and enables the network to be smart about how it handles traffic to minimize the footprint of applications.

Figure 1-3 shows how SONA breaks down this functionality into three layers:

  • Network Infrastructure: Campus, data center, branch, and so on. Networks and their attached end systems (resources such as servers, clients, and storage.) These can be connected anywhere within the network. The goal is to provide anytime/any place connectivity.

  • Interactive Services: Resources allocated to applications, using the network infrastructure. These include

    • Management

    • Infrastructure services such as security, mobility, voice, compute, storage, and identity

    • Application delivery

    • Virtualization of services and network infrastructure

  • Applications: Includes business policy and logic. Leverages the interactive services layer to meet business needs. Has two sublayers:

    • Application layer, which defines business applications

    • Collaboration layer, which defines applications such as unified messaging, conferencing, IP telephony, video, instant messaging, and contact centers

Figure 1-3

SONA Model

Planning a Network Implementation

It is important to use a structured approach to planning and implementing any network changes or new network components. A comprehensive life-cycle approach lowers the total cost of ownership, increases network availability, increases business agility, and provides faster access to applications and services.

The Prepare, Plan, Design, Implement, Operate, and Optimize (PPDIOO) Lifecycle Approach is one structure that can be used. The components are

  • Prepare: Organizational requirements gathering, high-level architecture, network strategy, business case strategy

  • Plan: Network requirements gathering, network examination, gap analysis, project plan

  • Design: Comprehensive, detailed design

  • Implement: Detailed implementation plan, and implementation following its steps

  • Operate: Day-to-day network operation and monitoring

  • Optimize: Proactive network management and fault correction

Network engineers at the CCNP level will likely be involved at the implementation and following phases. They can also participate in the design phase. It is important to create a detailed implementation plan that includes test and verification procedures and a rollback plan. Each step in the implementation plan should include a description, a reference to the design document, detailed implementation and verification instructions, detailed rollback instructions, and the estimated time needed for completion. A complex implementation should be done in sections, with testing at each incremental section.

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