There is no "one size fits all" network design; there are only models to which you, like other network designers, engineers, and managers, adhere. Given the right tools, you can design, build, and manage your network; and this chapter has discussed the essential tools that you will need to design, build, and manage a switched network.
These are the components of a switched network: the physical switch platform itself; a common infrastructure, to implement features on your switches; and a network management platform, so that you can monitor and manage your network's performance.
There are two types of switched networks in your design toolkit: a Layer 2 (flat) switched network and a Layer 3 (hierarchical) switched network. Layer 2 switched networks are flat networks made up of switches to create a single broadcast domain. These networks use the data link layer, or MAC, address in making filtering and forwarding decisions. Layer 3 switched networks add a hierarchical component to the network through a routing element, which uses the network layer address in making filtering and forwarding decisions. It is this same router element that also filters broadcasts from the rest of the network and thus creates a boundary for the broadcast domain.
LAN designs use switches to replace traditional hubs and use a mix of routers to minimize broadcast radiation in your network. By using the right pieces of software and hardware, and by adhering to good network design, you can build network topologies that can be robust and adapt to nearly any change in network conditions, such as a link or hardware failure, or changes in requirements, such as adding more users and devices.
Regardless of whether you use Layer 2 switching, Layer 3 switching or routing, VLANs, or a combination of all these elements, you should still abide by some general network design principles. You should examine your network design and implementation for single points of failure, adding redundant hardware or links when necessary. Look at the applications that are using your network and the protocol traffic these applications create. Watch the bandwidth usage on your network to ensure there is enough bandwidth available for all network users. When you build your network, use a hierarchical or modular model so that as your network grows, you add on the necessary parts (instead of undertaking a major redesign effort).
Network design case studies are discussed in Chapter 12, "Switching Case Studies."