Consistency and Simplicity Are the Keys

When creating network documentation, one goal that is frequently overlooked is the need to
make the documentation consistent and easy to read. Make an effort to apply the same structure
and methodology consistently to all the documentation. In this chapter we have discussed
the need for consistency when gathering the information and setting up a document, but it is
also important to maintain this uniformity from one document to the next.
One of the main purposes of your network documentation is its role in a troubleshooting
effort when the network is down. Because you can’t schedule when a problem will occur,
it is quite possible that you will be using your documentation to solve a problem in the middle
of the night, when you are not completely rested and are not operating at your peak
effectiveness. At such a time, you do not want to be saddled with documents that are
incompatible or so cluttered with information that they are difficult to read. Keep in mind
when and how the network documentation is going to be used, and take some simple steps
to make it easy to comprehend.
One of the first things you should do is ensure that the symbols used on all the diagrams mean
the same thing on each one. Do not use one symbol to signify a router on one diagram and a
different symbol to represent the same router on another.
Next, create a template for all your network configuration tables and topology diagrams. Earlier
in this chapter we discussed the template for a network configuration table, but templates for
network topology diagrams can be even more useful. For example, if you have multiple branch
locations, use an identical format and device-placement scheme on all the topology diagrams
so that similar information is always in the same spot on each diagram. This will save you time
in locating the facts you need.
Besides maintaining consistency, it is also important to avoid too much complexity. If the network
documentation contains extraneous information, that can make it difficult to find the
specifics that you need for your troubleshooting. The documentation should have enough
information to help you understand how things are connected and what the baseline of the
network is, without overwhelming you with data that may or may not be relevant.

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Components of a Network Topology Diagram

Like the network configuration table, the network topology diagram can contain a number of
items; its scope will depend on the complexity of the network involved. In its simplest form, a
network topology diagram will only include the devices and the connections between them.
However, in most cases, the diagram will contain much more information. Some common items
are as follows:
Device Name
Connections Between Devices (which can also include circuit numbers on WAN links)
Device Type
Interface Name
Speed
Media Type
MAC Address
VLANs
Trunk
Encapsulation
IP Address
Subnet
Subnet Mask
Routing Protocols
Unlike the network configuration tables, it is quite common for the network topology diagram
to depict a combination of layer 2 and layer 3 devices. This allows for a more complete
view of the interactions in the network and a better overall view of network connectivity. Just
as you do with network configuration tables, however, you need to be careful to incorporate
enough information into the topology diagram without adding too much. These are working
documents; if they become too overloaded with information, their maintenance will be more
difficult. On the other side, you don’t want to be hunting down information in the middle of an
emergency. There is a delicate balance between too much and not enough information.

Another point of note: Unless your network is small, you are not going to be able to fit it into
a single network topology diagram. Typically, you will need to make multiple topology diagrams
that cover separate aspects of the network. Depending on the drawing program you are
using to create the diagrams, you can also link each of these separate topology diagrams
together. In this manner, you can double-click a particular area to see more- or less-detailed
information or move to another segment of the network.

Network Topology Diagrams

Network configuration tables are great building blocks for your network documentation, but they
are not sufficient for getting a clear picture of how devices connect and interact within the network.
This is where the network topology diagram comes in. Simply put, a network topology diagram
is nothing more than a graphical representation of the network, allowing you to easily see
how components in the network are connected and how they interact. Arguably, it is the most
heavily utilized piece of documentation used in network troubleshooting and maintenance.