Documenting the Network Topology

Having a network topology map is crucial for understanding the existing network and formulating a basis for the new network design. Usually, the client will have some sort of network topology map. If not, make sure you create one and verify that the map is accurate with the client. Two basic types of network topology maps exist: One is a logical map with generic router symbols and overall network layout. This type of map is an excellent way to overview traffic flow and LAN and WAN topologies. A more detailed physical diagram includes router specifications, network addresses, and so on. Ideally, you would want both types of network diagrams, but sometimes features of both diagrams are merged into one. The following are guidelines for the topology map or an accompanying document:

• Every segment on the customer's network should be represented.

• All segments should have the appropriate LAN or WAN topology (for example, Ethernet, Token Ring, FDDI, Frame Relay cloud, serial links, and so on).

• All segments should be identified with the correct line and segment speeds.

• Try to include addressing schemes, such as network addresses, and the corresponding subnet masks for IP.

• Include all routers and switches, along with their naming schemes, if possible.

• Document any concerns about the network diagram, including traffic-flow issues and architectural questions.

Figure 2-1 shows a simple example of a topology diagram. This logical diagram is provided so that you can see the elements discussed previously.

Figure 2-1 Sample Network Topology Diagram


PIX Firewall


I | External Router



Internet Router

File Servers






File Servers

Documenting the Addressing Schemes

Addressing schemes are very important factors to consider. As long as you need network access, your devices must have addresses. IP addressing has become the most popular type of addressing. Many companies have implemented a Dynamic Host Configuration Protocol (DHCP) server, which is used to manage IP addressing within a network. This technology helps administrators quickly implement IP changes without having to track them in a spreadsheet.

Internet access and the need for network address translation (NAT) is a perfect example of how critical addressing becomes. NAT allows private addresses (those addresses not routable on the Internet) to be translated into a few public addresses. Many companies implement this technology because of the public IP address shortage. Addressing information is often included in topology diagrams.

Documenting Concerns About the Network

Document any concerns about the network diagram, including traffic-flow issues and architectural questions.

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