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Why is it useful to use both a physical and a logical network design?

Why is it useful to use both a physical and a logical network design?

Before we take a look at why physical and logical network designs are important, let's clarify exactly what they are.

A physical layout of the network shows the physical location of and the connections between devices participating on the network. In such diagrams, workstations are usually represented with small computer icons, servers with full tower cases, and switches and other similar devices are displayed as small rectangular boxes with their RJ-45 ports in the front (sometimes, switches are displayed without ports, depending on the angle at which we are viewing the network on the page).

A logical layout shows all logical aspects of the network. This includes logical networks, assigned IP addresses to various hosts and devices, routing tables and a lot more. In logical diagrams, there is very little interest in the actual interfaces and physical cables, so these details are usually omitted.

So why do we need all the above? Simple - for security, troubleshooting and management reasons. When a problem arises, I.E. a link is down, by simply looking at the physical layout, we are able to quickly identify where the problem is located, allowing us to quickly resolve it.

Having a visual view of a logical and physical network also helps identify possible security problems. When an unwanted visitor tries to obtain access to highly sensitive information, in most cases he or she will create a map of the network to better understand where each security checkpoint (firewall or similar device) is installed and what access can be obtained.

The above reason is also why these 'maps' are restricted to Administrators and Engineers who are responsible for the network. If they fall into the hands of 'enemy,' they can prove to be the most effective weapon against you!

This was first published in June 2004

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