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Diagnose NIC Problems

The Network Interface Card must be functioning for your PC to be able to communicate ona network. When network problems occur, the NIC is less likely to be the cause thaninfrastructure such as cables, routers and hubs. All problems below assume that you areexperiencing a complete or intermittent failure of network connectivity.

SymptomCheck

The cable is connected butthere is no light on the NIC

Unplug and replug the network connector into theNIC and at the other end.

Check that the other end of the cable isconnected to a device that is powered on.

Try switching the cable to a different port ifavailable.

Try a different network cable. Check the control panel in Windows to make sure

the card is recognized and working.

The data collision light isfrequently or continuously lit

Check that the far end of the network cable isconnected to the proper port, or try a differentport.

Check that your PC is not using an IP addressthat is already in use on your network.

Make certain that your PC is not using a name

that is already in use by another PC on thenetwork.

The lights on the NIC arenormal but I cannot connect tothe network

Make certain that other network devices arepowered on.

Make certain that your PC is configured with theproper Workgroup or Domain name.

Check that your PC is not using an IP addressthat is already in use on your network.

Make certain that your PC is not using a name

that is already in use by another PC on thenetwork. Allow up to 20 minutes for network polling to

identify all available resources.

Check the network cable connections and use adifferent port if available.

If Windows is configured for more than one NIC,make certain that the correct one is being usedfor this network.

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Diagnosing network problems: IPCONFIG

First you have to determine whether your computer is connected to a network. Open a Command

window*.

At the prompt, type ipconfig /all and press Enter. If everything is working correctly, youll see alist like this:

Windows IP Configuration

Host Name . . . . . . . . . . . . : IPTest

Primary Dns Suffix . . . . . . . :

Node Type . . . . . . . . . . . . : Hybrid

IP Routing Enabled. . . . . . . . : No

WINS Proxy Enabled. . . . . . . . : No

Ethernet adapter Local Area Connection:

Connection-specific DNS Suffix . :earthlink.net

Description . . . . . . . . . . . : Network

Connection

Physical Address. . . . . . . . . : 00-07-

E9-6D-A8-33

Dhcp Enabled. . . . . . . . . . . : Yes

Autoconfiguration Enabled . . . . : Yes

IP Address. . . . . . . . . . . . :

192.168.0.109

Subnet Mask . . . . . . . . . . . :

255.255.255.0

Default Gateway . . . . . . . . . :

192.168.0.1DHCP Server . . . . . . . . . . . :

192.168.0.1

DNS Servers . . . . . . . . . . . :

207.69.188.185

207.69.188.186

Lease Obtained. . . . . . . . . . : Tuesday,

February 08, 2005 2:04:55 PM

Lease Expires . . . . . . . . . . : Tuesday,

March 22, 2005 6:04:55 AM

Fig 1

Heres a description of the relevant information:

Host Name: The name of your computerConnection-specific DNS Suffix: The networkyoure connected to. At home, this is usually yourISP; at work, your company. Sometimes it may beblank.Dhcp / Autoconfiguration Enabled: These are twomethods that your computer gets an address.Physical Address: This is the serial number ofyour network card and will never change.IP Address: This is the address of your computer.Default Gateway: This is the address of your router.DNS Servers: These are the computers that interpretinternet names into their correct numeric address(such as Yahoo.com=66.94.234.13). Their function isprovided by your ISP or contained in your router.Lease Obtained / Expires: Obtained is when youlast connected to your router. Expires is a perioddetermined by your router settings and varies from anhour to weeks.Ethernet adapter...: If you have more than onenetwork adapter such as a wireless card, you may

see some or all of this information for each adapter. Ifit says Media disconnected, that means theres noconnection on the cable or no wireless networkavailable.

Likely problems

If you see all zeros for the IP addresses (Fig 2), you dont have a network connection. This is

means there is a bad cable between your computer and the router. It could also mean thecomputer and router are still negotiating their communication. Check that your wires are

connected and wait up to several minutes to try ipconfig again (hit F3 to repeat the same

command).

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If instead of IP Address, you see Autoconfiguration IP Address that would typically start168.254; (Fig 3) you have an electrical connection with the router, but do not have access to the

network. If it is not cleared up after a reboot, there may be a failure in the network. For some

reason, your computer is not communicating with a DHCP server.You may be connecting to a downstream switch that is not connected to the router. The router

may have its DHCP server turned off or the network may be expecting DHCP services fromanother device such as another router or a server.

You also may not have permission to connect to that network This is very unlikely in a homewired network, but might happen if you dont have the correct password for a wireless network.

You could also see it if you are trying to connect to a corporate network.

If you have a simple network and know you dont have any of these problems, the easiestsolution is probably to do a hardware reset of the router. This usually involves inserting a

straightened paper clip into a hole to press a recessed button. You may need to hold the button

several seconds, or hold it while powering up. Then you will need to restore the routerconfigurations or reconfigure it from scratch.

Ethernet adapter Local Area

Connection:

Connection-specific DNS Suffix :

Description . . . . . . . . . . : 3Com

3C920

Physical Address. . . . . . . . : 00-

06-5B-36-71-B5

Dhcp Enabled. . . . . . . . . . : Yes

Autoconfiguration Enabled . . . : Yes

IP Address. . . . . . . . . . . :

0.0.0.0

Subnet Mask . . . . . . . . . . :

0.0.0.0

Default Gateway . . . . . . . . :DHCP Server . . . . . . . . . . :

192.168.0.1

Fig 2

Ethernet adapter Local Area

Connection:

Connection-specific DNS Suffix :

Description . . . . . . . . . . : 3Com

3C920

Physical Address. . . . . . . . : 00-

06-5B-36-71-B5

Dhcp Enabled. . . . . . . . . . : Yes

Autoconfiguration Enabled . . . : Yes

Autoconfiguration IP Address. . :

169.254.39.17

Subnet Mask . . . . . . . . . . :

255.255.0.0Default Gateway . . . . . . . . :

Fig 3