I ran into this last week when I was helping someone “fix” their server. They couldn’t reach, or ping, their host, and when running an “ipconfig /all” command it was returning that the machine’s IP was ‘duplicate’.

Worth Noting: So sometimes when a server reports that its’ IP is a ‘duplicate’ it can be a DHCP mishap. It can happen when a server is assigned a static IP that is within a DHCP pool, and because there was no reservation, DHCP hands the IP out to some other machine. Thus two machines are trying to use the same, duplicate, IP address. When that happens you’ll need to resolve it by creating an IP reservation for the “correct” machine, and then releasing the IP from the machine that “incorrectly” took the IP from the pool so it can be assigned a new IP.

The machine I was fixing lived in a subnet that did not use DHCP and only had machines that were statically assigned their IPs in it. So the possible resolution mentioned above did not fit my scenario. So, what could it be? Well if you have a static IP set, and the DHCP service is enabled, Windows likes to give you an address on the 169.x.x.x network. Which just breaks the ip traffic on your server. Here’s how to fix it…

Step 1.

Open a command prompt

Step 2. Enter

"ipconfig /all"

Find what your system’s preferred IP is and if autoconfiguration is enabled, and the name of the interface that they are on. You will need this for the next step.

Step 3. Enter

netsh interface ipv4 show interface

Find the index number that is assigned to the interface you identified in the step above, you will need it in the next step.

Step 4.

Run the command below, but replace ’69’ with the index number that you identified in the step above.

netsh interface ipv4 set interface 69 dadtransmits=0 store=persistent

Step 5. Enter

services.msc

Disable the DHCP Client service. If you ever revert from a static IP back to a DHCP IP, you will need to re-enable this service and set it back to automatic.

Step 6.

Restart your computer.
After your system reboots, its static IP should now be the correct IP you had configured on it, and your IP traffic to/from it should be back to normal.

Congratulations, autoconfiguration has been disabled.