5 Network Layout Network layout takes topology and technology choices; architecture and design decisions; vendor, equipment, and serviceprovider choices; and strategic locations; and from these develops various views of your planned network design, including detailed logical diagrams, physical blueprints, and functionspecific component plans. All products of this process should also show the parts of your existing network that will be incorporated into the new design. 10.5.1 Logical Diagrams Logical diagrams show the connectivity and relationships among network devices. Relationships show how devices may interact with one another, how they may work together to provide service and support in the network, and what you might expect from them. For example, you could have a logical diagram showing the routers in your network, or showing just the border routers, or just the interfaces to all external networks. Such diagrams may also include security devices and how they will be connected to the routers, providing insight regarding how the routers and security devices would work together at an external interface. Diagrams that focus on logical relationships do so at the expense of accuracy in physical descriptions (i.e., location accuracy). Such diagrams can provide approximate correlations between devices and their physical locations; however, they do not provide an accurate representation of physical space. I refer to such descriptions as logical diagrams and not blueprints, as they do not provide the traditional spatial accuracy and level of detail expected in blueprints. Diagrams showing logical relationships among devices are quite useful as companions to network blueprints, or as early drafts of blueprints. Figure 10.12 is an example of a network diagram. This figure is an example of a communications closet. It shows the types of network devices planned for that closet, and how they are logically connected. For example, from the diagram you can tell that there are multiple firewalls and switches in the communications closet. You can also see the connectivity between devices, to the local networks, and to the Internet. At this stage, however, it does not describe the actual equipment or vendor selections, cable paths or types, or the physical arrangement of the devices in racks or shelves. Diagrams such as these are useful for planning purposes; however, they are not detailed enough to be considered blueprints. Another example of a logical diagram is shown in Figure 10.13. Instead of describing a particular location, this diagram shows the logical interconnection of devices from across a network. This diagram is useful in that it describes the Network Layout 409 Switch Net Mgmt Internet External IF Switch Router Firewall External Web Firewall To IDFs To ProdConf LabsCubicles DNS Server FIGURE 10.12 A Logical Diagram of a Communications Closet hierarchy of connections, which can be easily mapped to traffic flows in the network.