6.14.9 Practice Questions Networking Troubleshooting

The client system has moved too far away for the access point. Explanation In this case, the wireless client system has had no problems accessing the wireless access point until the move to the new office. In some cases moving a system will cause signal loss either from the increased distance away from the WAP or from unexpected interference by such things as concrete wall or steel doors. There are several ways to correct the problem including reducing the physical distance to the client, using a wireless amplifier, upgrading the antennas on the wireless devices or adding another WAP to the infrastructure. Because the client could previously access the WAP and still has occasional access, it is likely that the move was the cause of the problem rather than any configuration setting on the client system.

The user is out of the effective range of the wireless access point on her floor. Explanation Because the user is only experiencing intermittent problems, the most likely cause is that she is out of the effective range of the wireless network access point. All of the other answers listed may be appropriate if the user was unable to connect to the network at all. However, as the user is experiencing only intermittent problems, none of the other answers is likely to be the cause of the problem.

Your ISP'S DHCP server isn't working properly. Explanation Anytime you see a network interface assigned an IP address in the 169.254.0.1 to 169.254.255.254 range, you know that it was unable to acquire an IP address from a DHCP server. Automatic Private IP Addressing (APIPA) on the workstation automatically took over and assigned an IP address in the range listed above. Because of this, the workstation isn't configured with the correct router and DNS server addresses, and can't access the company's VPN.

Loopback plug Explanation Use a loopback plug to test the network card's ability to send and receive signals. Pinging the local host (ping 127. 0.0.1) tests the TCP/IP protocol stack, but does not actually send signals out the network card. A cable tester tests continuity of all wires in a cable and ensures that wires are connected appropriately in the plugs. Use a multimeter and an ohmmeter to test the electrical properties of cables and signals.

ping www.widgets.com Explanation To test both name resolution and communication with the server, use the ping command with the host name. The first step in the ping test is to find the IP address of the specified host. Using ping with just the IP address will not test name resolution. Using nslookup only tests name resolution, it does not test communication with the end device.

Incorrect DNS server address. Explanation In this scenario, a ping test to the Web site succeeds while accessing the Web site through the browser does not work. Users type host names in the browser to go to Web sites, and host names must be translated to IP addresses by a DNS server. Either the workstation is using the wrong address for the DNS server, the DNS server is not available, or the DNS server does not have an entry for the Web site. Because the ping and trace route tests works, you know that the IP address, subnet mask, and default gateway values are correct.

Incorrect subnet mask Explanation In this example, the network us using a mask of 255.255.255.0 (24-bits), but the workstation is configured to use a mask of 255.255.0.0.

Incorrect default gateway. Explanation In this example, the default gateway address is incorrect. The default gateway address must be on the same subnet as the IP address for the host. The host address is on the 192.168.1.0/24 subnet, but the default gateway address is on the 192.168.2.0 subnet.

nslookup Explanation Use Nslookup to troubleshoot DnS name resolution problems. Use Arp to view information about MAC addresses and their corresponding IP addresses. Netstat 9network statistics is a command-line tool that displays network connections (both incoming and outgoing), routing tables, and a number of network interface statistics. Use Nbtstat to help troubleshoot NetBIOS name resolution problems.

Tracert Ping Explanation On an IP based network, you can use the ping command to check connectivity between a source and destination computer.. You can also use tracert on a Windows system to check the routing path between two hosts. The tracert command performs the same function as ping, but includes the path information. Use nslookup and dig on Windows and Linux to resolve the IP addresses of host names using DNS lookups. Use Arp to view information about MAC addresses and their corresponding IP addresses.

ipconfig /release Explanation Use ipconfig /release to release the IP configuration information obtained from the DHCP server. Use ipconfig /renew to request new IP configuration information from the DHCP server. Use net stop to stop a network service. Use net logoff to break the connection between your computer and a shared resource.

ping -l Explanation Use ping -l to configure the payload size to identify when packets above a certain size are being lost. Ping -t continuously sends pings to a specific device. Tracert tests connectivity between devices while showing the path between the two devices. Nslookup resolves (looks up) the IP address of a host name. Netstat shows IP-related statistics.

Ping Explanation The output shown was produced by the ping utility. Specifically, the information output was created using the ping -t command. The -t switch causes packets to be sent to the remote hots continuously until stopped manually. Ping is a useful tool for testing connectivity between devices on a network. Using the -t switch with ping can be useful in determining whether the network is congested, as such a condition will cause sporadic failures in the ping stream. Tracert is similar to ping in that it tests connectivity between two hosts on the network. The difference is the tracert reports information on all intermediate devices between the host system and the target system. Ping, on the other hand, does not report information on intermediate devices. Nslookup is a tool provided on Linux, Unix, and Windows systems that allows manual name resolution requests to be made to a DNS server. This can be useful when troubleshooting name resolution problems. Ifconfig is a tool used on Unix, Linux, and Macintosh systems to view the configuration of network interfaces, including TCP/IP network settings.

Tracert Explanation The output is from a tracert command run on a Windows Server system. The tracert command provides information on each step in the route a packet takes to reach a remote host. Responses from each hop on the route are measured three times to provides an accurate representation of how long the packet takes to reach, and be returned by that host. This information can be useful in locating congestion points on a network, or when verifying that network routing is operating as expected. The ping command is used to test connectivity between devices on a network. Like tracert, ping sends three packets to the target host, but it does not report information on any intermediate devices it traverses to reach the target. Nslookup is a tool provided on Linux, Unix, and Windows systems that allows manual name resolution requests to be made to a DNS server. This can be useful when troubleshooting name resolution problems.

Directional antenna Omnidirectional antenna Explanation Directional and omnidirectional are two type of antennae commonly used in wireless networks. A directional antenna: - Creates a narrow, focused signal in a particular direction, which increases the signal strength and transmission distance. - Provides a stronger point-to-point connection; is better equipped to handle obstacles. An omnidirectional antenna: - Disperses the RF wave in an equal 360-degree pattern. - Provides access to many clients in a radius.