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I have a FreeBSD 10.1 VPS in Europe using the VirtIO Ethernet device that sees significantly smaller outbound bandwidth than inbound from the same distant hosts. This problem was originally noticed as slow downloads from our nginx web server.

The outbound bandwidth is consistently a fraction of the inbound from the same host, yet in itself the outbound bandwidth spans a significant range. Thus I find no obvious problem in the network configuration or host physical connection, though I have tried changes to various net.inet.* parameters to no meaningful effect.

I realize network paths can have some impact but the differences seen do not seem to fit that explanation. Note too the pf firewall does no limiting of any type on outbound traffic.

Link below is to pastebin of tcptraces of tcpdump data capturing iperf3 testing to three hosts (different geographic regions) as both client and server. The tcpdump was set to capture 8192 packets; the iperf command was iperf3 -c host -V -n 10M -p 520X followed by iperf3 -c host -V -n 10M -p 520X -R

Note for the last pair of traces shown the -n parameter was increased to 75M due to the significantly higher throughput available.

I've looked at the traces and see nothing (to me) that is odd other than perhaps my host (XYZ) having a small initial window.

Pastbin of tcptrace

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I can mark this as closed and solved (for now) though with no obvious reason/solution.

I was advised by the hosting provider to change from the virtio driver to e1000. In the process of preparing to do this, the VPS was stopped (from the console) and then restarted. Though still using the virtio driver, bandwidth is now much, much better and is symmetric.

The server had been up around 300 days.

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