Troubleshoot Common Network Problems Summary (36.6)
The following is a summary of each topic in the chapter and some questions for your reflection.
What Did I Learn in This Chapter? (36.6.1)
• The Troubleshooting Process—Troubleshooting is the process of identifying, locating, and correcting problems that occur. There are structured techniques that can be used to determine the most probable cause and solution. Document all steps taken in troubleshooting, even the ones that did not solve the issue.
To gather information about a problem, start by talking to the individual who reported the problem as well as any other affected users. Next, collect information about any equipment that may be affected. This can be gathered from documentation. A copy of all log files and a listing of any recent changes made to equipment configurations are also necessary. Information about the network can also be gathered using network monitoring tools.
Choose a troubleshooting approach to organize your efforts to fix the problem. Here are three structured troubleshooting techniques: top-down, divide-and-conquer, and bottom-up. All of these structured approaches assume a layered concept of networking. Other good approaches are follow-the-path, substitution, comparison, and educated guess.
• Physical Layer Problems—Physical layer problems are concerned mainly with the hardware aspects of computers and networking devices and the cables that interconnect them. To troubleshoot at Layer 1, first check that all devices have power supplied, and that the devices are turned on. If the problem is with wireless, verify that the wireless access point is operational and that wireless settings are configured correctly.
Regardless of whether the fault is present on the wireless or wired network, one of the first steps in a bottom-up strategy of troubleshooting should be to examine the LEDs, which indicate the current state or activity of a piece of equipment or connection. Cabling is the central nervous system of wired networks and one of the most common causes of connectivity problems. Be sure to use the correct type of cable. Improper cable termination is one of the main problems encountered in networks. To avoid this, cables should be terminated according to standards. Maximum cable run lengths exist based on characteristics of the different cables. Verify that the correct ports are being used between the networking devices. Protect cables and connectors from physical damage.
• Troubleshoot Wireless Issues—Wireless communications rely on RF signals to carry data. Many factors can affect our ability to connect hosts using RF:
• Not all wireless standards are compatible.
• Each wireless conversation must occur on a separate, non-overlapping channel.
• The strength of an RF signal decreases with distance.
• RF signals are susceptible to interference from outside sources, including other devices functioning on the same frequency.
• APs share the available bandwidth between devices.
Modern WLANs incorporate various technologies to help secure the data on the WLAN. Incorrect configuration of any of these can prevent communication. Some of the most common settings that are configured incorrectly include: the SSID, authentication, and encryption.
• Common Internet Connectivity Issues—A number of software utility programs are available that can help identify network problems. Some of the available utilities include ipconfig, ping, netstat, tracert, and nslookup.
On Windows devices, you can view the IP configuration information with the ipconfig command at the command prompt. If the IP configuration appears to be correctly configured on the local host, next, test network connectivity by using ping. Ping is used to test if a destination host is reachable.
When troubleshooting a network with both wired and wireless connections, use a divide-and-conquer technique to isolate the problem to either the wired or wireless network. The easiest way to determine if the problem is with the wired or the wireless network is to
• Ping from a wireless client to the default gateway, which verifies if the wireless client is connecting as expected.
• Ping from a wired client to the default gateway, which verifies if the wired client is connecting as expected.
• Ping from the wireless client to a wired client, which verifies if the wireless router is functioning as expected.