Troubleshooting - Network

Troubleshooting Tips for a New Network Card

1. If you can't connect to a server or if Windows reports an error after you double-click Network Neighborhood, try the following first:
   • Make sure you're using the drivers that are on the drivers disk that ships with the network interface card (NIC).
   • Make sure the driver is loaded and the protocols are bound. Check the Device Properties list for trouble indicators (an "X" or "!" symbol).
   • Test the NIC adapter with the diagnostic utilities that often came with the driver installation.
   • Check with your LAN administrator - you may need to install additional networking software.
2. If the problem persists, follow these guidelines:
   • Make sure the cable is installed properly. The network cable must be securely attached at both RJ45 connections (adapter and hub). The maximum allowable distance from adapter to hub is 100 meters. If the cable is attached and the distance is within acceptable limits but the problem persists, try a different cable. If you're directly connecting two computers without a hub or switch, use a crossover cable.
   • Try another network cable.
   • Check the LED Lights on the NIC. Before the LEDs can be used for troubleshooting, the network interface card (NIC) must be connected to the network and the network driver must be installed. Most NICs come with LEDs near the connection. The meaning of the LED signals may be different from one manufacturer to the other. Here is a common LED description for 3COM 10/100BT dual speed NIC. Please consult your NIC manual for any difference.

LED	Description	Flashing	Steady (On)	Off
10 LNK	Green: Link integrity	Reversed polarity	Good 10BT connection	No connection between NIC & hub
100 LNK	Green: Link integrity	Reversed polarity	Good 100BT connection	No connection between NIC & hub
ACT	Yellow: Port traffic for either speed	Network traffic present	Heavy network traffic	No traffic

3. The computer hangs when the drivers are loaded.
   • Change the PCI BIOS interrupt settings. See your NIC and system manuals for more details.
   • If you are using EMM386, it must be version 4.49 or newer.
4. Diagnostics pass, but the connection fails or errors occur.
   • At 100BT, use Category 5 wiring and make sure that the network cable is securely attached.
   • At 100BT, connect to a 100BT hub/switch (not 100Base-T4).
   • For NetWare, make sure you specify the correct frame type in your NET.CFG file.
   • Make sure the duplex mode setting on the adapter matches the setting on the switch.
5. The LNK LED doesn't light.
   • Make sure you've loaded the network drivers.
   • Check all connections at the adapter and the hub/switch.
   • Try another port on the hub/switch.
   • Make sure the duplex mode setting on the adapter matches the setting on the hub/switch.
   • Make sure you have the correct type of cable between the adapter and the hub. 100Base-TX requires two pairs. Some hubs require a crossover cable while others require a straight-through cable.
6. The ACT LED doesn't light.
   • Make sure you've loaded the correct network drivers.
   • The network may be idle. Try accessing a server.
   • The adapter isn't transmitting or receiving data. Try another adapter.
   • Make sure you're using two-pair cable for TX wiring.
7. The adapter stopped working without apparent cause.
   • Run the diagnostics program that came with the NIC.
   • Try reseating the NIC in its slot, or try a different slot if necessary.
   • The network driver files may be corrupt or missing. Remove the drivers and then reinstall them.
8. The Wake on LAN (WOL) feature is not working.
   • Make sure the WOL cable is attached and that power is being applied to the computer.
   • Check the BIOS for its WOL setting. Some computers may need to be configured for WOL.
   • Make sure the network cable is fully attached to the adapter.
9. Crossover cable troubleshooting tips. When you work with network cabling, concentrators (hubs or switch), and NICs from different venders, it is possible to connect everything and still have no communication between file servers and workstations. 
   When there are several unknown variables, it is difficult to determine which component is broken. Use these tips to isolate the problem.
   • Determine whether your equipment complies with the 10Base-T or 100Base-TX standard. This is particularly important for hubs and switches.
   • Connect a straight-through cable from the PC to the hub. The hub performs an internal crossover so that the signal can go from TD+ to RD+ and TD- to RD- (see How to Make Network Cables). When you look at an RJ-45 connector from the front, pin 1 is identified on the left-hand side when the metal contacts are facing up.
   • Make sure that the TD+ and TD- wires are twisted together , and that the RD+ and RD- wires are twisted together. Using wires from opposing pairs can cause signals to be lost. For a 100Base-TX cable, pins #1 and #2 , and #3 and #6 must be on the same twisted strand.
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10. When there is doubt whether a hub is performing correctly, or if the impedance settings are in question, a crossover cable can help you isolate the failing component:
    • Connect a file server and a client PC back to back with a crossover cable to verify that the NIC and network operating system are properly configured.
    • To make a crossover cable, simple connect TD+ to RD+ and TD- to RD-. The cable performs the crossover that is usually performed by the hub. Make sure that two twisted-pair wires are used. If the file server and client PC function together as a small network, then either the existing cabling or the hub is the problem.
    • If there is a proper crossover, the appropriate LED comes on. If there is a straight-through connection, the LED does not light. A blinking LED indicates that there is a polarity mismatch (that is, TD+ to RD- instead of TD+ to RD+).