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I am running a domain controller, that also has a Hyper-V role installed.

Within the Hyper-V, I have a legacy Windows 2008 SBS that we will eventually retire.

When the guest OS is shutdown network traffic is normal.

When the guest OS is running, there is huge packet loss (around 50%, in bursts of 5 seconds on and off).

I am running Windows Server 2008 R2 fully patched, no antivirus, two NICs (one for the native machine, another for guest VMs) that plug in to the same switch.

Hardware is DELL R410, NICs are Broadcom BCM5716C NetXtreme II running the latest drivers from the Broadcom website. I have tried drivers from DELL also, and all have the same issue.

Anything I can try to fix the issue or troubleshoot further to pinpoint a resolution? Why does packet loss occur when the guest is running?

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Does network traffic increase significantly when the guest is powered on? – EEAA Nov 29 '12 at 14:12
When did you update the firmware on the card last? – Chris S Nov 29 '12 at 14:25
up vote 4 down vote accepted

Check to make sure that the VM and the physical machine don't have the same MAC address or the same IP address set. This sounds suspiciously like either a duplicate IP issue, or an accidental arp poisoning.

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Bang on - forgot I had exported this and had set the MAC address to the same as the host machine (I did a phy to VM with disk2vhd)... hence MAC addresses were the same. Thanks for the reply you saved me a very late night! – g18c Nov 29 '12 at 14:39

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