I had a similar problem on a Fujitsu TX300 s4 server with Broadcom NetXtreme Gigabit Ethernet card
It has an option for LSO & Jumbo frames. I had to google if that was the same as what you talked about
An alternative to using jumbo frames is large send offload (LSO), also known as TCP. segmentation offload (TSO).
I disabled these options and since then data is flowing again.
Thanks for the tip, RichardFrank!
I don't have a TCP Segment OffLoading option on my Server 2008 Standard x64 system's Intel 82566DM gigabit card, but disabling Large Send Offload v2 seemed to work for me.
I was having the opposite issue here. Moving files from host to guest was fine, but transferring files from guest to anywhere else was very slow. All firewall settings looked good. I saw this and had some hope. I disabled Large Send Offload v2 on my host, but this did not improve anything. Eventually I disabled Large Send Offload v2 on the guest and speed improved immediately!
I had to sign up for this forum to say thank you. The "large send" feature was causing my slowdown running on a windows server.
Disabling "Large Send Offload v2 (IPv4)" on my "Realtek PCIe GBE Family Controller" fixed it for me too. Thanks a bunch!