We're running a couple labs full of dual-boot iMacs. We've noticed that in the labs where we have short DHCP lease times, we're having issues with the machines dropping their internet connections. I've determined that it happens when they boot from OSX to Windows. When this happens, doing an "ipconfig /all" shows a legitimate lease expiration, but the lease is showing up as having been obtained in Dec of 1875. The internet works just fine right up until the lease expires, at which point Windows doesn't bother to renew it and the connection drops. A release/renew fixes it. Since these are dual boot, any time we boot from OS X to Windows, the clock is initially 6 hours off due to the way OSX and Windows store the time. This is fixed halfway through boot due to apple time service, windows time server, or some number of other things which require an accurate time. However, setting the time back 6 hours during boot seems to be messing up DHCP. After testing setting the clock a bit by hand and looking at "ipconfig /all", it looks like all you have to do is set the clock to a time before the DHCP lease was obtained, and it will screw it up. The lease expiration adjusts itself when you adjust the clock, but the time the lease was obtained does not. Is there any particularly good way to deal with this other than just setting longer DHCP lease times or setting up a script to do a release/renew at some relatively safe point after boot?

Hi, Please ensure the network card setting is correct from Windows side. If the issue persists, you may need to contact Apple support for help. Niki Han TechNet Community Support

Any network card settings in particular I should be looking at? And other than Apple being responsible for the clock being wildly off during boot, this doesn't seem to be an Apple problem. I've been able to replicate it on a couple different non-apple machines as well - it would just only cause problems with clock skew that is greater than the DHCP lease time though, which is generally not the case but happens to be showing up in our lab with Dual boot iMacs and 2 hour lease times. My home PC that I'm sitting on currently shows: Lease Obtained: Saturday, January 14, 2012 2:25:28AM Lease Expires: Tuesday, January 18, 2012 2:25:35PM Current Time: Tuesday, January 17, 2012 2:27 AM If I manually change my computer's date to January 11, it now reads: Lease Obtained: Tuesday, December 07, 1875 7:57:12PM Lease Expires: Friday, January 12, 2012 2:25:35PM Current Time: Thursday, January 11, 2012 2:30 AM Were I now to wait the day and a half until that lease expires, I believe that Windows would not renew the DHCP lease and my internet would drop. This seems a bit like it's just a bug and not some setting I can fix. Assuming that's the case - I'll probably look into a script for OSX to manually change the system clock to the local time that Windows expects at shutdown.

Hello I had the 1874 DHCP Lease time problem on all my dual boot Macs on campus. I had worked around it using a ipconfig /release ... ipconfig /renew delayed login script. Also as mentioned setting the time back 6 hours in OSX seemed to work, but was sloppy. But I now have a final solution. Boot up the bootcamp partition and log into WindowsOpen regedit Navigate to : HKLM > SYSTEM > CurrentControlSet > Control > TimeZoneInformationCreate a new DWORD string value called RealTimeIsUniversal and give it a value of 1Open Services.msc and set the properties of Apple Time Service to DISABLEDReboot Windows should now lease an IP address from the correct year, and will subsequently release correctly when the lease time is up. Cheers.