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Old 01-17-2018, 09:57 AM   #1
MoneyGuy
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I'm getting a box popping up that reads as follows:

Windows has detected an IP address conflict
Another computer on this network has the same IP address as this computer.

It suggests I go to the Windows system event log.

Nothing has changed recently that I'm aware of that should cause this now when it's never happened before. Any advice is appreciated.
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Old 01-17-2018, 10:00 AM   #2
GoinAllTheWay
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It pops up sometimes. I've had this on my computer too. Not sure why it happens but usually a re-start clears it up for me.
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Old 01-17-2018, 10:04 AM   #3
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Quote:
Originally Posted by MoneyGuy View Post
I'm getting a box popping up that reads as follows:

Windows has detected an IP address conflict
Another computer on this network has the same IP address as this computer.

It suggests I go to the Windows system event log.

Nothing has changed recently that I'm aware of that should cause this now when it's never happened before. Any advice is appreciated.
One device on your network has a static IP that is set in your DHCP range.
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Old 01-17-2018, 11:05 AM   #4
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Quote:
Originally Posted by Rathji View Post
One device on your network has a static IP that is set in your DHCP range.
I have an excellent mental image of MoneyGuy blinking as he realizes he now knows less than he did before asking the question.
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Old 01-17-2018, 11:19 AM   #5
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Quote:
Originally Posted by jammies View Post
I have an excellent mental image of MoneyGuy blinking as he realizes he now knows less than he did before asking the question.
Yep, I realized that as I was tying it, but was too busy for a complete response.

Yoy have a device on your network with a Static IP address, likely a printer etc. This address is set and never charges. Your DHCP hands out IP addresses within a certain range to all devices on the network that need an address (and don't have a static IP). The range it picks addresses from is set usually to something like 192.168.1.100 to 192.168.1.200, and it just keeps track of which addresses it has given out to which devices, but only for a little while (normally 8 days) , to make sure that it doesn't give out the same address to another device while this one is in use.

So what happens if someone doesn't know what they are doing, or doesn't have network documentation, they set a static IP for something like a printer, inside that DHCP range. In our example above, let's say 192.168.1.169. Now, when the DHCP server is giving out addresses, it has no idea that thus address is in use, so it will just assign this address to another device. Many computers will realize there is another device with the same IP address, and give you a warning like you saw.

The solution is to use a network scanning tool, like netscan, and determine which IP addresses are being used by which devices, and then see which of those addresses is not inside your DHCP scope (normally found on your server or router). You can then either change the static IP address to something that is not in use (and outside dhcp range, change the dhcp scope, or set a DHCP reservation for that device, so DHCP stops handing out that address.

Alternatively, you can go to each device and check which ones are static, and then either change the static ip to something outside the dhcp range, or set the network to use dhcp on that device.
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Old 01-17-2018, 11:24 AM   #6
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To be a bit more helpful: try rebooting every device connected to your network, including phones, printers, and so on. Sometimes, rather than a static IP being the issue, a device doesn't properly renew its IP and the router reissues that IP while its still in use. Rebooting devices forces them to request a renewal, and thus will often fix the issue.

Not to go into too much detail, but the reason the addresses need to be "renewed" is that you don't want to have a device you once had, but no longer do, to keep its address forever, as eventually you might run out. So every few days, the devices are supposed to say "hey dude, I'm still here, can I keep this IP address?" and the router/server says "No problemo! Just let me update my records that you're still around!" If a device doesn't check in, and the address' validity expires, the router/server assumes that device isn't around anymore and that its address is free to give to some other device. Which is where a duplicate comes from.
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Old 01-17-2018, 11:29 AM   #7
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You could also have 2 DHCP servers that have served the same IP to different devices. Have you added anything to your network recently?
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Old 01-17-2018, 11:45 AM   #8
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Or what Rathji said. That could be as well, depending on who set up your network and their level of care in doing it correctly.
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Old 01-17-2018, 12:14 PM   #9
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This happens often if you have Personal Hotspot on your phone turned on and then plug it into the computer to charge, the computer picks up a network connection from the phone through USB.
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Old 01-17-2018, 12:30 PM   #10
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Quote:
Originally Posted by jammies View Post
I have an excellent mental image of MoneyGuy blinking as he realizes he now knows less than he did before asking the question.
Tis true.
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