Several Dell users complained about this problem.
One user had this problem with a Dell Optiplex 960 running Windows 7, 32 bit. Upgrading to the latest network card drivers fixed the problem.
From another user: "On my Windows 7 Professional Optiplex 780 (Q45 chipset). I rolled back the network card driver to Microsoft version 10.5.1.0. This was suggested some time back, so I gave it a try.
The bad news is that it behaved just like before but without the error messages this time. Upon waking up from sleep mode, the connectivity was extremely slow. The good news is that this driver has a power management option that can be unchecked to prevent the OS from powering down the "device". With the power-down option disabled, the disconnect problem seems have been resolved."
From a support forum:
I've been working with multiple vendors to come out with a solution for this issue. After searching forums and other users experience and feedback from Dell Support I found this Dell / HP support internal bulletin:
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Intermittent Network Connection *Known Issue*
Especially with the Intel 82567 network cards. The MAC Addressing system is typically 00:XX:XX:XX:XX:XX; the new MAC Addressing system is starting with A4:XX:XX:XX:XX:XX; this is causing problems with proxies, routers, and wireless bridges that are not able to properly send traffic when the first octet of the MAC is not 00 or 0X.
You should report this to your network equipment vendor as soon as possible for a firmware upgrade, or search to see if one is already available. You can also do a workaround by changing the MAC Address to the network card in the windows registry.
To change the MAC Address of the Network Card, follow these steps:
1. Create a text file in Notepad by cutting and pasting following text and save it as it DELLMAC.REG
Windows Registry Editor Version 5.00
2. Click Start, Run and type REGEDIT.EXE /S DELLMAC.reg and press <Enter>. Answer Yes to enter the information into the registry.
3. Reboot the system
Note: Make sure to increment the MAC Address so that they are not duplicated: 00DE11078001, 00DE11078002, 00DE11078003, etc…
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This is my conclusion:
1) Rollback to old Intel NIC driver 10.5.1.0
2) Try to change the mac of your workstation, however in my environment I would need to increment hundreds of registry files, no fix for this at the moment.
3) Update Switch/Router firmware