Network Diagrams– Cisco Basic Network Hardware
Networking diagrams are crucial to the documentation required to operate, troubleshoot, and modify a network.
Building a good network diagram requires a solid grasp of how the network is built, how it works, and what the diagram itself is supposed to accomplish. There are two broad categories of network diagrams: physical and logical.
Figure 10-7 illustrates a physical network diagram.
Figure 10-7 A Physical Network Diagram In Figure 10-7:
• CO: Core router
• ED: Edge router
• FW: Firewall
• SV: Server
• PP: Patch panel
• NET: Internet connection router
Physical diagrams show where each wire originates and terminates in a network or section. It is common for large-scale networks to require hundreds of physical diagrams to accurately describe how each cable runs, what it connects to, etc.
Physical diagrams are good for understanding a network’s physical component, location, and how cables are physically run. For instance, the physical diagram is a good place to start if
• You want to ensure two redundant cables do not run through a single cable tray or conduit—called circuit grooming.
• You want to plan out how many cables are needed of a specific length.
• You want to know about the physical size of a piece of equipment—perhaps so you can plan for a replacement.
Physical diagrams do not always contain the following:
• Port numbers, because these can be inferred from where a cable is shown connecting to a piece of equipment. For instance, you can infer the connection from CO1 port 2 is connected to CO2 port 3 from this simple diagram.
• Any kind of addresses. You normally will not find IP addresses, physical interface addresses, or any other addresses on a physical network diagram.
Figure 10-8 shows a logical diagram of the same network.
Figure 10-8 Logical Network Diagram Logical network diagrams are abstracted in some ways:
• Notice the patch panels are not shown in the logical diagram.
• You can no longer tell which cable runs might be longer or shorter.
• You can no longer tell what device each rack is in.
Use a logical diagram to follow the traffic flow or understand the control plane configuration and operation. Logical diagrams can also contain the following:
• Which routing protocol is running between pairs of routers
• Any policy implemented at a given point in a network, such as packet filtering, route aggregation, etc.
• Where links are connected (such as the labels given in Figure10-8)
• IP addresses
• Where services are running or located in the network
Many network operators assign device names based on their location, bringing more information from the physical world into their logical diagrams.
Two simple rules of thumb are extremely helpful when working with network diagrams:
• Physical diagrams follow the flow of the wires; logical diagrams follow the flow of the packets.
• You should include whatever is helpful without crowding the diagram. You can always have more than one diagram with different pieces of information.