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2012-06-12

A+: Network and Internet Troubleshooting

Can’t Access Network Resources

 
If an error message such as Duplicate Computer Name or Duplicate IP Address is displayed during system startup, open the Network icon and change the name of the computer or the system’s IP address. Contact the network administrator for the correct name or IP address settings to use.

Significant Drops in Network Performance

 
Significant drops in network performance can be traced to a variety of causes, including
• Damage to cables, connectors, hubs, and switches
• Expanding network capacity with hubs in place of switches
• Connecting high-speed NICs to low-speed hubs or switches
• RFI/EMI Interference with Wireless Networks
If network usage patterns remain constant but some users report lower performance, check cables, connectors, and other network hardware for physical damage. Dry, brittle, and cracked cables and connectors can generate interference, which forces network stations to retransmit data because it wasn’t received correctly. Replace damaged cables and connectors.

Use diagnostic programs supplied with the network adapter if the same brand and model of adapter is used by multiple computers. These diagnostics programs send and receive data and provide reports of problems.

If all the users connected to a single hub or switch report slowdowns, check the hub or switch. Replace a hub with a switch to see an immediate boost in performance. Continue to use switches to add capacity.
Make sure that computers with Fast Ethernet (10/100) hardware are connected to dual-speed hubs or switches to get the benefits of 100 Mbps performance. 10/100 cards will run at 10 Mbps if connected to 10Mbps hubs or switches. Enable full-duplex mode if the cards and hubs or switches support it to boost performance to 20 Mbps (with 10BASE-T) or 200 Mbps (with 10/100 cards running Fast Ethernet).
Make sure that computers with Gigabit Ethernet (10/100/1000) hardware are connected to Gigabit Ethernet switches to get the benefits of 1000 Mbps performance.

Radio frequency interference (RFI) is closely related to EMI, and RFI/EMI interference can have a big impact on wireless network (WLAN) performance. For the A+ exam, some things to consider include cordless phone and microwave usage. Because these devices can also inhabit the 2.4 GHz frequency range used by 802.11b, g, and n networks, they can interfere with the network signal. Because 2.4GHz cordless phones use spread-spectrum technology to help avoid eavesdropping, it is not possible to configure these phones to use a particular 2.4GHz channel.

To help avoid interference from other wireless networks, configure your 2.4GHz wireless network to use one of the non-overlapping channels ((1, 6, or 11). Some anecdotal evidence suggests that channel 11 is less likely to receive RFI from 2.4GHz cordless phones.

You should also consider using cordless phones that use frequencies that will not interfere with 2.4GHz or 5GHz wireless networks, such as phones using DECT (1.9GHz) or DECT 6.0 (6.0GHz) frequency bands.

Unattended PC Drops Its Network Connection

Incorrect settings for power management can cause stations to lose their network connections when power management features, such as standby mode, are activated. Check the properties for the network adapter to see if the adapter can be set to wake up the computer when network activity is detected.

All Users Lose Network Connection

 
If the network uses a bus topology, a failure of any station on the network or of termination at either end of the network will cause the entire network to fail. Check the terminators first, and then the T-connectors and cables between computers. If you suspect that a particular computer is the cause of the failure, move the terminator to the computer preceding it in the bus topology. Repeat as needed to isolate the problem. Replace cables, connectors, or network cards as needed to solve the problem.

If the network uses a star topology, check the power supply going to the hub, switch, or wireless access point, or replace the device.

If only the users connected to a new hub or switch that is connected to an existing hub or switch lose their network connection, check the connection between the existing hub or switch and the new one. Most hubs and switches have an uplink port that is used to connect an additional hub or switch. You can either use the uplink port or the regular port next to the uplink port, but not both. Connect the computer using the port next to the uplink port to another port to make the uplink port available for connecting the new hub or switch.

If the uplink port appears to be connected properly, check the cable. Uplink ports perform the crossover for the user, enabling you to use an ordinary network cable to add a hub or switch.

If you use a crossover cable, you must connect the new hub or switch through a regular port, not the uplink port.

Users Can Access Some Shared Resources But Not Others

Users who need to access shared resources on a network using user/group permissions must be granted permission to access resources; different users are typically allowed different access levels to network resources. Contact the network or system administrator for help if a user is prevented from using a resource; the administrator of the network or peer server will need to permit or deny access to the user.

Can’t Print to a Network Printer

Problems with network printing can also come from incorrect print queue settings and incorrect printer drivers.

When you configure a network printer connection, you must correctly specify the UNC path to the printer. For example, if the printer is shared as LaserJ on the server Xeon3, the correct UNC path to specify in the printer properties sheet would be
\\Xeon3\LaserJ

If a shared printer connected to a Windows system is available at some times, but not at other times, open the printer’s properties sheet and adjust the Scheduling Option setting.

Ping and Tracert Work, But User Can’t Display Web Pages with Browser

If Ping and Tracert receive output from the specified websites but the web browser cannot display web pages on those or other sites, the browser configuration might be incorrect.
If the browser doesn’t use the correct configuration for the connection type, no pages will be displayed. With dial-up Internet connections, either the user must manually open the connection or the browser should be set to dial the connection. If a proxy server or special network configuration is needed, this must be configured in the browser. 


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