Network connectivity problems occur when one or more computers cannot communicate with other areas of the network. There are three levels of connectivity problems:

• Loss of connectivity - When users cannot access areas of some part of network.
• Intermittent connectivity - Although users have access to network resources some of the time, they are still facing periods of downtime. Intermittent connectivity problems can indicate that your network is on the verge of a major break.
• Timeout problems - Timeouts cause loss of connectivity, but are often associated with poor network performance.

Network connectivity problems have various causes but the most common causes for connectivity problems are:

• Network adapters and switch ports have mismatching duplex levels or transfer speed settings.
• Network adapters or switches with transmission rates of 10/100 megabits per second (Mbps) do not switch over correctly. Some autosense settings may not correctly detect the speed of some network adapters.
• The network adapter is incompatible with the motherboard or other hardware or software components and drivers.

To troubleshoot network connectivity problems, follow these steps:

1. Use the Ping or PathPing command-line tools to test basic connectivity. Use Ping to isolate network hardware problems and incompatible configurations. Use PathPing to detect packet loss over multiple-hop trips.
2. Check the event logs for network-card-related entries or connectivity-related entries.
3. Check whether the network adapter is on the supporting list of the Computer operating system.
4. Check other computers that use the same default gateway that are plugged into the same hub or switch. If these computers do not experience network connectivity problems, the problem may be a faulty network adapter on one computer.
5. Contact the vendor of each motherboard and update the BIOS of the boards to obtain the latest version.
6. Check the network adapter and uplink hardware (hub or switch) for common settings. Make sure that all complementing network resources (network adapter, hub, and switch) are set to the same speed and duplex level.
7. Manually set the network adapter of the computer that has connectivity problems to half-duplex and a lower speed.
8. Swap the network cable between the failing system and the hub or switch.
9. Replace the network adapter with a network adapter that has been tested and proven reliable. To do this, follow these steps:
   1. Remove the network adapter diagnostics program.
   2. Remove the network adapter in Network properties.
   3. Install the new network adapter.
10. Run Network Monitor at the same time on both ends of the network connection. After you filter the traces on the addresses of the two systems, compare both traces to see if you can see the same traffic.

If the above common procedure still cannot solve the problem, you may need to use some professional network management and troubleshooting tools (hardware/software) to assist you.

It is often helpful in network connectivity troubleshooting to have the following items available:

• Spare hardware equipment (such as modules and power supplies), especially for your critical devices
• A recent backup of your device configurations to reload if flash memory gets corrupted (which can sometimes happen due to a power outage)