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How to Test a Network Adapter
Last updates: 7/26/01

Q.  How do I test an Ethernet network interface card (NIC)?

A.  Most NICs or network adapters come with one or more floppy disks containing drivers, etc. for various operating systems.  These floppies also usually include a diagnostic program to test the NIC.  Many of these programs are DOS-Based and must be run by booting the computer to DOS or from a DOS window in Windows.  Unless you have a loopback plug installed, the loopback test will probably fail.  A loopback plug directs signals from the NIC's transmitter back to it's receiver.  An indicator that a NIC and cabling is functioning is to check the LINK (sometimes labeled LNK, etc.) and Activity (ACT, etc.) LEDs, if there are any, on the NIC and on the device at the other end of the cable.  The LINK should be solid with no flickering and the ACTIVITY should be blinking, which indicates, of course, network activity.  This indication is not as thorough a test as the diagnostics program and it is not foolproof (see Why would the Link (or LNK) LEDs be on solid, if there is a faulty cable connecting two Ethernet devices?)The diagnostics program and LED observations may not conclusively show that the NIC is fully functional in Windows.  Look for exclamation marks beside the NIC driver in the Windows 9x/Me Device Manager (click Start, Settings, Control Panel, System, Device Manger...), which indicate a resource conflict and run the Windows Resource Conflict Troubleshooter if you find any.  Look for multiple instances of the NIC driver in the network configuration (click Start, Settings, Control Panel, Network and remove all of them, if you find any, restart Windows and reinstall the driver, etc.  Run hwinfo (click Start, Run, and enter hwinfo /ui).  To help narrow-down problems, click View in the main menu and select Devices with Problems.  Once these steps are completed and the NIC passes, try copying about 100 MBytes of files to another computer on the network.  Net diag and ping are useful tools for further testing a NIC and a network.  For more info, open a DOS windows and type:

C:\>ping /?

and

C:\>net /?

Ping requires that the TCP/IP protocol be installed, and IP addresses be assigned at both ends of the network segment to be tested.

net diag is a useful low-level network test.

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