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We have a heterogenous network that has many Apple products within it.

Recently, we had an issue with a duplicate IP that appeared to be interfering with someone's work. Simple enough, right? Not on OS X, apparently.

After digging around the Internet and a phone call with Apple Support, who suggested it was our routers (!!), I'm hoping someone here may have a deeper understanding of what's going on here.

I released the address from our internal Linux/ISC DHCPD server manually (it was deleted, server restarted).

I found and XML file generated at /var/db/dhcpclient/leases/en2-1,18:af:61:b7:7d:0 (for whichever device/MAC). Removing this file had no effect. OS X still insists on renewing the address it has had. Our default lease is 24 hours.

Rebooting the Mac after the above had no effect. ipconfig, unplump/plumb the interface had no effect.

This leads me to believe that OS X is storing this information in some obscure database that I'm unaware of. As for the documentation, well it basically sucks and didn't tell me much of anything.

Does anyone know how to force the Mac to forget about it's DHCP acquired IP address, completely, and request a new address from the server?

Thanks in advance.

marked as duplicate by klanomath, jherran, bmike Oct 6 '15 at 1:44

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  • We tried this and it still pulls in the original IP address. – Forrest Aldrich Oct 5 '15 at 20:47
  • Which system version runs on the affected device? Did you also check the 2 devices for duplicate/spoofed MAC-addresses? – klanomath Oct 5 '15 at 20:53
  • OSX Yosemite is the client. It's a small network; arpwatch found different MAC addresses. It would be easy to just configure a static address, but the actual issue is we want to know how to force the OSX client to forget about it's current DHCP reservation. In this case, we cannot figure out where that information is being stored. – Forrest Aldrich Oct 5 '15 at 21:21
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I find that changing the value of DHCP Client ID will sometimes generate a new DHCP address when rebooting the Mac and/or router will not.

System Preferences > Network > Advanced

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