Virtual PC Is Throttling My Host's Gigabit LAN Connection to ~100Mbps

Question

This is very strange: it seems whenever I have the Virtual PC Console running (I don't even need to have a Virtual Machine running), my gigabit network connection gets throttled to from ~500Mbps down to ~100Mbps.

Here's a iperf log, where I opened and then closed the Virtual PC Console:

[ ID] Interval       Transfer     Bandwidth
[108]  0.0- 1.0 sec  52.2 MBytes   438 Mbits/sec
[108]  1.0- 2.0 sec  53.7 MBytes   450 Mbits/sec
[108]  2.0- 3.0 sec  53.1 MBytes   445 Mbits/sec
[108]  3.0- 4.0 sec  53.8 MBytes   451 Mbits/sec
[108]  4.0- 5.0 sec  53.5 MBytes   449 Mbits/sec
[108]  5.0- 6.0 sec  51.6 MBytes   433 Mbits/sec
[108]  6.0- 7.0 sec  20.5 MBytes   172 Mbits/sec
[108]  7.0- 8.0 sec  15.6 MBytes   131 Mbits/sec
[108]  8.0- 9.0 sec  15.6 MBytes   131 Mbits/sec
[108]  9.0-10.0 sec  15.6 MBytes   131 Mbits/sec
[108] 10.0-11.0 sec  14.4 MBytes   121 Mbits/sec
[108] 11.0-12.0 sec  39.8 MBytes   334 Mbits/sec
[108] 12.0-13.0 sec  53.3 MBytes   447 Mbits/sec
[108] 13.0-14.0 sec  54.3 MBytes   456 Mbits/sec
[108] 14.0-15.0 sec  53.6 MBytes   450 Mbits/sec
[108] 15.0-16.0 sec  53.7 MBytes   450 Mbits/sec
[108] 16.0-17.0 sec  53.4 MBytes   448 Mbits/sec
[108] 17.0-18.0 sec  53.2 MBytes   446 Mbits/sec
[108] 18.0-19.0 sec  53.8 MBytes   452 Mbits/sec
[108] 19.0-20.0 sec  53.5 MBytes   448 Mbits/sec

I'm running Windows Vista Home Premium SP2 and Virtual PC 6.0.156.0.

Does anyone have any idea what's going on, and how I can fix it?

Answer 1

It might be Virtual PC's bridged network driver.

It should be inactive when no VMs are running, but try disabling it anyway and check if it helps.