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The problem I'm having is a (windows 7- LAN - Office Environment) Desktop Computer is flagging up an error of a conflicting IP Address. When I use ipconfig to check the IP address, there is none showing. What I have tried is as follows:

Using Windows to diagnose connection issues

Checking the Network Adapter properties to make sure the IP/DNS is set to obtain automatically

Using the command line to release/renew the IP Address(which doesn't work probably because there is no IP Address to release?)

Disabling/Enabling the Network Adapter/restarting the computer

I also connected another desktop up to that connection and that desktop connects with no issues - can browse the internet/access all necessary files on the server etc.

Does this mean it is a hardware problem?

  • You state that it's an office environment, but you didn't say how big it is. I find it weird that your device isn't receiving an IP at all, but is complaining about a conflicting IP address. But it worked just fine with a different PC on the same connection. While it's pretty rare, it could be possible that there is a device on the network that has the same MAC address. It could also be that the NIC is just faulty. The easiest way to troubleshoot would be to install a PCIe NIC, disable the current NIC, and see if the problem goes away. – DrZoo Jan 19 '18 at 19:27
  • Your original question was titled, “IP Address Conflict - LAN - Network Adapter” and I changed it to be an actual question, “I’m getting an IP address conflict but when I check the IP address, nothing shows up?” When titling a question, please always be sure to actually ask a question in the title. Otherwise, what does “IP Address Conflict - LAN - Network Adapter” actually mean? – JakeGould Jan 19 '18 at 19:55
  • @Drzoo I took the pc I'm getting the error on to another connection and it provided the same error. I assigned a static IP address to test the NIC and it connects so that appears to be working. I'll have a look at the Mac addresses on Monday to see if any are the same. As for the office size around 25 users. – rayzor Jan 20 '18 at 22:13
  • @DrZoo It was a rare occasion where it was truly a MAC address conflict. I used the command arp -a on the server and was able to compare the MACs. I changed the MAC address on said computer and set the IP address back to obtain IP address automatically. Everything is working fine. Thanks for your help! – rayzor Jan 23 '18 at 23:18
  • Wow, that is incredible! Given the size of your office I thought the duplicate MAC wouldn't end up being the issue. Just to give you an insight, you should check out this reddit post. You have much higher odds of winning the lottery, than having a duplicate MAC on your network. – DrZoo Jan 24 '18 at 0:00
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Based on the behavior of the NIC, it led to believe that there was a duplicate MAC address on the network. This is a very rare occurrence and is something I learned from a past networking instructor, who has this happen once in her 25 year career in the Army.

As another good bit of information, this issue would flip flop between both PCs, if one came on the network before the other. It’s something that can really baffle people if a duplicate MAC address doesn’t cross their mind.

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Someone in your network has set their IP Address to a custom one that is inside the DHCP range. The DHCP server assigns you an ip address and assumes it is free because the server itself does not have an active leash for it.

The person who set this static ip addres was unaware of the DHCP scope and that is what's conflicting.

The only way to stop this is to find out who has this IP assigned and make them unassign the addres.

It is also possible that a new device in the network, such as a printer was misconfigured. Your IT Department should be able to resolve this issue. If you are the IT department, then you can try a ping with the -a option (ping -a xxx.xxx.xxx.xxx) to retrieve the netbios name of that machine. If it's a computer, their computername will show up. Additionally an IP-Scan could be used to get more information about this ip address. I usually use the one from advanced-ip-scanner.com.

Thanks for the suggestion from Appleodity, you can check your eventlog to find out which ip is the duplicate: https://docs.microsoft.com/en-us/previous-versions/windows/it-pro/windows-server-2008-R2-and-2008/cc727689(v=ws.10)

  • How do I find out the IP Address that is causing the issue? When I look for the IP on the computer in question, nothing is there e.g. when I run ipconfig - IPv4 address is missing. This was all working fine yesterday. I did have a look at all the IP addresses on the network and they show as Dynamic.. In the LAN properties everything is as it should be. Much appreciated. – rayzor Jan 19 '18 at 18:52
  • Do an ipconfig /renew in the command prompt. It should attempt to give you an ip address and if it fails it should tell you the ip address it tried to set. – LPChip Jan 19 '18 at 18:57
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    @rayzor check your Windows event log. It tells you the IP address and MAC address of the machine that is conflicting with it. docs.microsoft.com/en-us/previous-versions/windows/it-pro/… – Appleoddity Jan 19 '18 at 21:35
  • I'll give this a go on Monday @appleoddity when I'm back in the office. Thanks – rayzor Jan 20 '18 at 22:07

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