Troubleshooting network problems is often accomplished with the help of hardware and software. To troubleshoot effectively, you need to know how these tools can be used to solve network problems.
After this lesson, you will be able to:
- Name the principal hardware tools used to troubleshoot network problems and identify which hardware tool to use on a particular part of the network.
- Identify software-based monitoring tools.
- Identify the components that each monitor tool checks.
- Describe the methods for monitoring a network.
- Describe the tools used for troubleshooting a network problem.
Estimated lesson time: 30 minutes
Hardware tools were once very expensive and difficult devices to use. They are now less expensive and easier to operate. They are helpful to identify performance trends and problems. This section describes the most common of these tools.
The digital voltmeter (volt-ohm meter) is the primary all-purpose electronic measuring tool. It is considered standard equipment for any computer or electronic technician and can reveal far more than just the amount of voltage passing through resistance. Voltmeters can determine if:
One of the network administrator's most important functions is to confirm source voltage for the network equipment. Most electronic equipment operates on 120 volts AC. But not all outlets will meet these requirements. In older installations, especially in large industrial areas, the system load can drop voltages to as low as 102 volts. Operating for long periods at low voltages can cause electronic equipment problems. Low voltages often cause intermittent faults. At the other end, voltage that is too high can cause immediate damage to the equipment. In new construction, it is possible for circuits to be wired incorrectly and actually put out 220 volts AC.
NOTE
With any new location or new construction, it is important to check the outlet voltages before connecting any electronic equipment in order to verify that they are within an acceptable range.
Time-domain reflectometers (TDRs), as shown in Figure 13.1, send sonar-like pulses along cables to locate breaks, shorts, or imperfections. Network performance suffers when the cable is not intact. If the TDR locates a problem, the problem is analyzed and the results are displayed. A TDR can locate a break within a few feet of the actual separation in the cable. Used heavily during the installation of a new network, TDRs are also invaluable in troubleshooting and maintaining existing networks.
Figure 13.1 Time-domain reflectometer
Using a TDR requires special training, and not every maintenance department will have this equipment. However, administrators need to know the capabilities of TDRs in case the network is experiencing media failure and it is necessary to locate a break.
Advanced cable testers work beyond the physical layer of the OSI reference model (described in Chapter 5, "Introducing Network Standards") in the data-link layer, network layer, and even the transport layer. They can also display information about the condition of the physical cable.
Oscilloscopes are electronic instruments that measure the amount of signal voltage per unit of time and display the result on a monitor. When used with TDRs, an oscilloscope can display:
Several other versatile hardware tools can serve as useful aids to network troubleshooting.
Crossover cables are used to connect two computers directly with a single patch cable. Because the send and receive wires are reversed on one end, the send wire from one computer is connected to the receive port on the other computer. Crossover cables are useful in troubleshooting network connection problems. Two computers can be directly connected, bypassing the network and making it possible to isolate and test the communication capabilities of one computer, rather than the whole network.
A hardware loopback device is a serial port connector that enables you to test the communication capabilities of a computer's serial port without having to connect to another computer or peripheral device. Instead, using the loopback, data is transmitted to a line, then returned as received data. If the transmitted data does not return, the hardware loopback detects a hardware malfunction.
Tone generators are standard tools for wiring technicians in all fields. A tone generator is used to apply an alternating or continuous tone signal to a cable or a conductor. The tone generator is attached to one end of the cable in question. A matching tone locator is used to detect the correct cable at the other end of the run.
These tools are also able to test for wiring continuity and line polarity. They can be used to trace twisted-pair wiring, single conductors, and coaxial cables, among others. This pair of equipment is sometimes referred to as "fox and hound."
Software tools are needed to monitor trends and identify network performance problems. This section describes some of the more useful of these tools.
Network monitors are software tools that track all or a selected part of network traffic. They examine data packets and gather information about packet types, errors, and packet traffic to and from each computer.
Network monitors are very useful for establishing part of the network baseline. After the baseline has been established, you will be able to troubleshoot traffic problems and monitor network usage to determine when it is time to upgrade. As an example, let's assume that after installing a new network, you determine that network traffic is utilized at 40 percent of its intended capacity. When you check traffic, one year later, you notice that it is now being utilized at 80 percent capacity. If you had been monitoring it all along, you would have been able to predict the rate of increased traffic and predict when to upgrade before failure occurs.
Protocol analyzers, also called "network analyzers," perform real-time network traffic analysis using packet capture, decoding, and transmission data. Network administrators who work with large networks rely heavily on the protocol analyzer. These are the tools used most often to monitor network interactivity.
Protocol analyzers look inside the packet to identify a problem. They can also generate statistics based on network traffic to help create a picture of the network, including the:
Protocol analyzers have built-in TDRs, discussed in the previous section.
The protocol analyzer can provide insights and detect network problems including:
Protocol analyzers can identify a wide range of network behavior. They can:
Sniffer, which is part of a family of analyzers from Network General, can decode and interpret frames from 14 protocols including AppleTalk, Windows NT, NetWare, SNA, TCP/IP, VINES, and X.25. Sniffer measures network traffic in kilobytes per second, frames per second, or as a percentage of available bandwidth. It will gather LAN traffic statistics, detect faults such as beaconing, and present this information in a profile of the LAN. Sniffer can also identify bottlenecks by capturing frames between computers and displaying the results.
The LANalyzer software performs much the same function as Sniffer but is available only on a NetWare LAN.
Run the c13dem01 video located in the Demos folder on the CD accompanying this book to view a demonstration of network troubleshooting tools.
After a network has been installed and is operational, the administrator needs to make sure it performs effectively. To do this, the administrator will need to manage and keep track of every aspect of the network's performance.
The scope of a network management program depends on:
Small peer-to-peer networks consisting of 10 or fewer computers can be monitored visually by one support person. However, a large network or WAN might need a dedicated staff and sophisticated equipment to perform proper network monitoring.
One way to ensure that the network does not fail is to observe certain aspects of its day-to-day behavior. By consistently monitoring the network, you will notice if any areas begin to show a decline in performance.
Most current network operating systems include a monitoring utility that will help a network administrator keep track of a network's server performance. These monitors can view operations in both real time and recorded time for:
These monitors can:
When monitoring a network, it is important to establish a baseline, as discussed in Chapter 12, "Administering Change." This documentation of the network's normal operating values should be periodically updated as changes are made to the network. The baseline information can help you identify and monitor dramatic and subtle changes in your network's performance.
Some servers include network monitoring software. Windows NT Server, for example, includes a diagnostic tool called Network Monitor, shown in Figure 13.2. This tool gives the administrator the ability to capture and analyze network data streams to and from the server. This data is used to troubleshoot potential network problems.
The packets of data in the data stream consist of the following information:
Figure 13.2 Windows NT Network Monitor
Network management software follows standards created by network equipment vendors. One of these standards is the simple network management protocol (SNMP).
In an SNMP environment, illustrated in Figure 13.3, programs called "agents" are loaded onto each managed device. The agents monitor network traffic in order to gather statistical data. This data is stored in a management information base (MIB).
SNMP components include:
Figure 13.3 SNMP environment showing components
To collect the information in a usable form, a management program console regularly polls these agents and downloads the information from their MIBs. After the raw information has been collected, the management program can perform two more tasks:
If any of the data falls above or below thresholds set by the manager, the management program can notify the administrator by means of alerts on the computer or by automatically dialing a pager number. The support staff can then use the management console program to implement changes in the network.
The following points summarize the main elements of this lesson: