- Check physical cables plugged in. Is the NIC disabled in Device Manager?
- Check the link lights on the NIC and switch
- Is the NIC bad? Use utility provided by OS to verify NIC works.
- Perform a loopback test (Sends data out of the NIC and checks to see if it comes back). The loopback interface is usually at 127.0.0.1. This lets you know if the protocol stack is working, even if your network connection is not.
- Ping a local IP address. Run an ipconfig and find your IP address and try to ping that address. That lets you know that the local configuration and ethernet adapter in your computer is working as expected.
- Ping something outside of your computer. A device that should always be there is your default gateway. The IP address of the default gateway is also found in ipconfig.
- If you can ping your default gateway, try pinging something outside of your local network/ on the router’s other side. Can you ping a website? Try pinging Google’s DNS IP address at 18.104.22.168. If the ping fails you might not be able to get an IP address for the web site meaning a DNS failure. To fix failing DNS
- Use command prompt: ipconfig /flushdns
- Network and Share Center > Click change adapter settings > right click on network connection > Select Diagnose (to run troubleshooter)
- Try using another DNS server
APIPA/link local address
If you haven’t configured a static IP address on your computer, and you turn it on and it’s not able to find a DHCP server, then it will automatically assign itself an APIPA address. APIPA addreses are 169.254.1.0 through 169.254.254.255 with 169.254.0.0/24 and 169.254.255.0/24 reserved. When your computer picks an APIPA address it uses ARP (address resolution protocol) to confirm the address isn’t currently in use by any other device on your network. If no one responds to the ARP, the computer gets assigned that IP address.
- See if you cang ping the default gateway. If that’s successful ping the WAN port on your router. Renew your DHCP address in the router’s configuration.
Intermittent connectivity is when you have Internet access and then it suddenly drops and then a little while later you can access the Internet again. Intermittent connectivity is difficult to troubleshoot, but first check the system tray. If you see a broken LAN icon this means there is a loss of signal and we should check the cabling that is used to connect to the network. Check the network interface card in the computer to see if it’s working well. If that works, check the infrastructure being used for the wired or wireless network. Check the switch or wireless access point. It could be that the switch has a bad interface or the switch or AP is randomly restarting which would cause our computer to have intermittent connectivity.
IP conflict means two or more computers have the same IP. IP conflict doesn’t usually occur when you have DHCP but if you have some devices that are statically assigned and some that are DHCP assigned, you may run into conflict. Windows will identify duplicate IPs to prevent conflicts, and will put up an alert on screen saying that “There is an IP address conflict with another system on the network.” If for some reason two devices do have the same IP address, you may find that you have intermittent connectivity because the network doesn’t know where to send the data, your device or the device with the identical IP.
Find the 2 devices with the identical IP and resolve the IP conflict, then reboot or reset the NIC in one of the devices to restart the DHCP process.