Slow network performance inside VM when using bridge mode, but not when using NAT

[cwrunks]

Created a vm with the virtio network device, bridged to vmbr0 and I'm getting about a third of the speed I should. Here is a speedtest from the ProxMox host:

Retrieving speedtest.net configuration...
Retrieving speedtest.net server list...
Testing from X (XX.XX.XX.XX)...
Selecting best server based on latency...
Hosted by X (XXX, XX) [140.97 km]: 40.202 ms
Testing download speed........................................
Download: 69.41 Mbits/s
Testing upload speed..................................................
Upload: 6.13 Mbits/s

And then from the VM:

Retrieving speedtest.net configuration...
Retrieving speedtest.net server list...
Testing from X (XX.XX.XX.XX)...
Selecting best server based on latency...
Hosted by X (XXX, XX) [140.97 km]: 42.717 ms
Testing download speed........................................
Download: 24.03 Mbits/s
Testing upload speed..................................................
Upload: 2.16 Mbits/s

This is what I get if I use bridge mode no matter which network device I choose. If I use NAT mode then networking inside the VM is near native. KVM hardware virtualization is enabled. Any ideas?

Edit: Seems to only affect Internet traffic. iperf from vm to my nas (which is only 100mbit) reads 90Mbps.

 

[dcsapak]

how does your network setup look like? maybe there is some qos/traffic shaping/filtering active based on mac/ip address?