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We are having a strange behavior on our company network. From time to time a IP that is given out by the DHCP server "stops" working externally, internal network access is working and DNS lockups is working but the computer with that IP is unable to access the internet.

The only workaround that I have found is to put the specific IP adress in the exclusion list of the DHCP server and renew the IP on the PC, then everything works again.

I thought this behavior would go away when I reinstalled the DC but NO, it just happened again.

Does anyone have a clue to what could cause this, I'll list our environment below.

DC Windows Server2008 R2 Firewall Level1 FBR-4000 PC client Windows 7

/Mattias

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migrated from superuser.com Dec 10 '10 at 15:42

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2 Answers

Sounds like someone is manually grabbing that IP or arp spoofing (without properly passing traffic read as: mitm fail). I would check around and see if there's some nefarious activity going on or a user that has a static IP set up.

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note: it SHOULD complain about IP addressing conflicts, but it's a possibility –  aking1012 Dec 10 '10 at 12:45
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I had a similar issue at work a few months back, which I think I tracked down to the wifi connection on an HP laptop that was set to use DHCP but seemed to remember old IP assignments and try to reuse them.

I didn't get around to proving my suspicions because the problem was very intermittent and I left the company before I could get my hands on the laptop to check and/or update the wireless drivers.

For the same reason, I can't give any specific laptop model number. I do, however, remember that the laptop did warn about IP address conflicts (which the user was acknowledgeing and then carrying on working with the laptop 'accepting' the conflict) and the fix was to reboot it.

Executive summary: Do you have any HP laptops you can check?

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