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Introduction to Cisco Network Design

Chapter Description

This chapter from Cisco Press provides an overview of the technologies available today to design networks. Discussions are divided into designing campus networks, designing WANs, utilizing remote connection design, providing integrated solutions, and determining networking requirements.

Networking—the communication between two or more networks—encompasses every aspect of connecting computers together. Networks have grown to support vastly disparate end-system communication requirements. A network requires many protocols and features to permit scalability and manageability without constant manual intervention. Large networks can consist of the following three distinct components:

  • Campus networks, which consist of locally connected users in a building or group of buildings

  • Wide-area networks (WANs), which connect campuses

  • Remote connections, which link branch offices and single users (mobile users and telecommuters) to a local campus or the Internet

Figure 1-1 provides an example of a typical enterprise network.

Figure 1-1 Example of a Typical Enterprise Network

Designing a network can be a challenging task. To design reliable, scalable networks, network designers must realize that each of the three major components of a network has distinct design requirements. A network that consists of only 50 meshed routing nodes can pose complex problems that lead to unpredictable results. Attempting to optimize networks that feature thousands of nodes can pose even more complex problems.

Despite improvements in equipment performance and media capabilities, network design is becoming more difficult. The trend is toward increasingly complex environments involving multiple media, multiple protocols, and interconnection to networks outside any single organization's dominion of control. Carefully designing networks can reduce the hardships associated with growth as a networking environment evolves.

This chapter provides an overview of the technologies available today to design networks. Discussions are divided into the following general topics:

  • Designing campus networks

  • Designing WANs

  • Utilizing remote connection design

  • Providing integrated solutions

  • Determining your networking requirements

Designing Campus Networks

A campus network is a building or group of buildings all connected into one enterprise network that consists of many local-area networks (LANs). A campus is generally a portion of a company (or the whole company) that is constrained to a fixed geographic area, as shown in Figure 1-2.

The distinct characteristic of a campus environment is that the company that owns the campus network usually owns the physical wires deployed in the campus. The campus network topology is primarily LAN technology connecting all the end systems within the building. Campus networks generally use LAN technologies, such as Ethernet, Token Ring, Fiber Distributed Data Interface (FDDI), Fast Ethernet, Gigabit Ethernet, and Asynchronous Transfer Mode (ATM).

Figure 1-2 Example of a Campus Network

A large campus with groups of buildings can also use WAN technology to connect the buildings. Although the wiring and protocols of a campus might be based on WAN technology, they do not share the WAN constraint of the high cost of bandwidth. After the wire is installed, bandwidth is inexpensive because the company owns the wires and there is no recurring cost to a service provider. However, upgrading the physical wiring can be expensive.

Consequently, network designers generally deploy a campus design optimized for the fastest functional architecture that runs on the existing physical wire. They might also upgrade wiring to meet the requirements of emerging applications. For example, higher-speed technologies—such as Fast Ethernet, Gigabit Ethernet, and ATM as a backbone architecture—and Layer 2 switching provide dedicated bandwidth to the desktop.

Trends in Campus Design

In the past, network designers had only a limited number of hardware options—routers or hubs—when purchasing a technology for their campus networks. Consequently, it was rare to make a hardware design mistake. Hubs were for wiring closets, and routers were for the data-center or main telecommunications operations.

Recently, local-area networking has been revolutionized by the exploding use of LAN switching at Layer 2 (the data link layer) to increase performance and to provide more bandwidth to meet new data networking applications. LAN switches provide this performance benefit by increasing bandwidth and throughput for workgroups and local servers. Network designers are deploying LAN switches out toward the network's edge in wiring closets. As Figure 1-3 shows, these switches are usually installed to replace shared concentrator hubs and give higher-bandwidth connections to the end user.

Figure 1-3 Example of Trends in Campus Design

Layer 3 networking is required in the network to interconnect the switched workgroups and to provide services that include security, quality of service (QoS), and traffic management. Routing integrates these switched networks, and provides the security, stability, and control needed to build functional and scalable networks.

Traditionally, Layer 2 switching has been provided by LAN switches, and Layer 3 networking has been provided by routers. Increasingly, these two networking functions are being integrated into common platforms. Multilayer switches that provide Layer 2 and 3 functionality, for example, are now appearing in the marketplace.

With the advent of such technologies as Layer 3 switching, LAN switching, and virtual LANs (VLANs), building campus networks is becoming more complex than in the past. Table 1-1 summarizes the various LAN technologies required to build successful campus networks. Cisco Systems offers product solutions in all these technologies.

Table 1-1 Summary of LAN Technologies

LAN Technology

Typical Uses

Routing technologies

Routing is a key technology for connecting LANs in a campus network. It can be either Layer 3 switching or more traditional routing with Layer 3 switching and additional router features.

Gigabit Ethernet

Gigabit Ethernet builds on top of the Ethernet protocol but increases speed tenfold over Fast Ethernet to 1000 Mbps, or 1 Gbps. Gigabit Ethernet provides high-bandwidth capacity for backbone designs while providing backward compatibility for installed media.

LAN switching technologies—Ethernet switching

Ethernet switching provides Layer 2 switching and offers dedicated Ethernet segments for each connection. This is the base fabric of the network.

LAN switching technologies—Token Ring switching

Token Ring switching offers the same functionality as Ethernet switching but uses Token Ring technology. You can use a Token Ring switch as either a transparent bridge or as a source-route bridge.

ATM switching technologies

ATM switching offers high-speed switching technology for voice, video, and data. Its operation is similar to LAN switching technologies for data operations. ATM, however, offers high-bandwidth capacity.


Network designers are now designing campus networks by purchasing separate equipment types (for example, routers, Ethernet switches, and ATM switches) and then linking them. Although individual purchase decisions might seem harmless, network designers must not forget that this separate equipment still works together to form a network.

It is possible to separate these technologies and build thoughtful designs using each new technology, but network designers must consider the overall integration of the network. If this overall integration is not considered, the result can be networks that have a much higher risk of network outages, downtime, and congestion than ever before.

2. Designing WANs | Next Section