Many customers can't provide detailed and up-to-date maps of the existing network. In many cases, you need to develop the maps yourself. Companies that are constantly working in "fire-fighting" mode don't have time to proactively document the existing network.
To develop a network drawing, you should invest in a good network-diagramming tool. You can use Cisco Works to map a network and collect other types of network audit information, including hardware and software versions, configurations, and so on. Other tools include HP OpenView, IBM's Tivoli products, Whatsup Gold from Ipswitch, and LANSurveyor from Neon Software. The Microsoft Visio product line is highly recommended for network diagramming. The product line includes Visio Standard, Visio Professional, and Visio Enterprise Network Tools.
Many network engineers recommend the netViz products from netViz Corporation. netViz is an information-management tool that allows you to visualize and work with complex data systems such as internetworks. Designed to deal with large amounts of information, netViz integrates graphics and data to create a visual database, making it easy to see system components, their unique characteristics, and their relationships to each other.
For large campus networks and service providers, Visionael Corporation offers client/server network documentation products that have network inventory, troubleshooting, and change-management features. Visionael products support network planning, design, deployment, provisioning, validation, and daily operations. Visionael products provide detailed data about the physical topology as well as the logical topology.
Developing a single network map may not be possible for large internetworks. There are many approaches to solving this problem, including simply developing many maps, one for each location. Another approach is to apply a top-down method. Start with a map or set of maps that shows the following high-level information:
• Geographical information, such as countries, states or provinces, cities, and campuses
• WAN connections between countries, states, and cities
• WAN and LAN connections between buildings and between campuses
For each campus network, you can develop more precise maps that show the following more detailed information:
• Buildings and floors, and possibly rooms or cubicles
• The location of major servers or server farms
• The location of routers and switches
• The location of mainframes
• The location of major network-management stations
• The location and reach of virtual LANs (VLANs). (If the drawing is in color, you can draw all devices and segments within a particular VLAN in a specific color.)
• Some indication of where workstations reside, although not necessarily the explicit location of each workstation
Another method for characterizing large, complex networks is to use a top-down approach that is influenced by the OSI model. First develop a logical map that shows applications and services used by network users. This map can call out internal web, e-mail, File Transfer Protocol (FTP), and print and file-sharing servers. It can also include external web, e-mail, and FTP servers.
Be sure to show web caching servers on your network maps because they can affect traffic flow. Documenting the location of web caching servers will make it easier to troubleshoot any problems reaching web servers during the implementation and operation phases of the network design cycle.
Next develop a map that shows network services. This map might depict the location of security servers, for example, TACACS and RADIUS servers. Other network services include Dynamic Host Configuration Protocol (DHCP), Domain Name System (DNS), and Network Address Translation (NAT), as well as Simple Network Management Protocol (SNMP) and other management services. The location and reach of any virtual private networks (VPNs) that connect corporate sites via a service provider's WAN or the Internet can be depicted, including major VPN devices, such as VPN concentrators. Dial-in and dial-out servers can be shown on this map as well.
You may also want to develop a map that depicts the Layer 3 topology of the internetwork. This map can leave out switches and hubs, but should depict routers, logical links between the routers, and high-level routing protocol configuration information (for example, the location of the desired designated router [DR] if Open Shortest Path First [OSPF] is being used).
Layer 3 drawings should also include router interface names in Cisco shorthand nomenclature (such as s0/0) if Cisco routers are used. Other useful information includes Hot Standby Router Protocol (HSRP) router groupings, redistribution points between routing protocols, and demarcation points where route filters occur.
A map or set of maps that shows detailed information regarding data link layer links and devices is often extremely helpful. This map reveals LAN devices as well as interfaces connected to public or private WANs. This map may hide the logical Layer 3 routing topology, which is shown in the previous map, but it should provide a good characterization of the physical topology. A data link layer map includes the following information:
• An indication of the data link layer technology for WANs and LANs (Frame Relay, ISDN, 100-Mbps or 1000-Mbps Ethernet, Token Ring, and so on)
• The name of the service provider for WANs
• The location and high-level configuration information for LAN switches (for example, the location of the desired root bridge if the Spanning Tree Protocol [STP] is used)
• The location and reach of any VLANs.
• The location and high-level configuration of trunks between LAN switches Characterizing the Logical Architecture
While documenting the network infrastructure, take a step back from the diagrams you develop and try to characterize the logical topology of the network as well as the physical components. The logical topology illustrates the architecture of the network, which can be hierarchical or flat, structured or unstructured, layered or not, and other possibilities. The logical topology also describes methods for connecting devices in a geometric shape (for example, a star, ring, bus, hub and spoke, or mesh).
When characterizing the logical topology, look for "ticking time bombs" or implementations that might hinder scalability. Check for large Layer 2 STP domains that will take a long time to converge. Also check for overly complex or oversized networks that might lead to EIGRP stuck-in-active (SIA) problems and other routing problems. If the customer has fully redundant network equipment and cabling but the servers are all single-homed (attached to a single switch), keep this in mind as you plan your redesign of the network.
The logical topology can affect your ability to upgrade a network. For example, a flat topology does not scale as well as a hierarchical topology. A typical hierarchical topology that does scale is a core layer of high-end routers and switches that are optimized for availability and performance, a distribution layer of routers and switches that implement policies, and an access layer that connects users via hubs, switches, and other devices. Logical topologies are discussed in more detail in Chapter 5, "Designing a Network Topology."
Figure 3-1 shows a high-level network diagram for an electronics manufacturing company. The drawing shows a physical topology, but it is not hard to step back and visualize that the logical topology is a hub-and-spoke shape with three layers. The core layer of the network is a Gigabit Ethernet network. The distribution layer includes routers and switches, and Frame Relay and T1 links. The access layer comprises 10-Mbps and 100-Mbps Ethernet and one Token Ring network. An Ethernet network hosts the company's World Wide Web server. As you can see from the figure, the network included some rather old design components. The company required design consultation to select new technologies and to meet new goals for high availability and security.
Figure 3-1. Network Diagram for an Electronics Manufacturing
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Figure 3-1. Network Diagram for an Electronics Manufacturing
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