Upload performance - help sought/perhaps a bug? (#18751)

[caspertone]

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ModEdit; related ticket: #18751: Very low upload throuput in NAT adapter - Windows 10 x64 1903 host/guest

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Hi All,

Platform is:
host: W10PRO 1903 X64 + Virtual Box 6.0.8 +Ext Pack
guest: W10PRO 1903 X64 (4GB, 2cores) + GA + Virtio network packages from fedora virtio-win-0.1.171.iso

Two adapters installed (for tests and workarounds): AD1 = Bridged AD=2 Natted - Only one is used, either by removing "wire" in VBox settings or by disabling interface in guest.

I get helthy good download speeds in the guest in the ranges of over 30Mbps, up to 100Mbps even.

Download is another beast. I would like to use just the natted interface, but I am unable to upload. My workaround is to disable in the guest the natted i/f and upload using the bridged one. Usually I get upload speeds of over 30Mbps. I use for uploading rclone and cloud storage.

There are some (scarce) breadcrumbs here and there about poor performance of upload. Of course bridge better performance over natted is well known... But, almost NO upload speed using natted?

With natted upload starts with 300kbps. one minute later comes down to 10kbps. one later, to less that 1 kbps.

I tried to sinthonize the performance using the recommended approach: touch parameters via VBoxManage modifyvm "name" mtu,sendbuff,receivebuff,initialsizeofTCPwindowsend,initialsizeofTCPwindowreceive.
Tested with 1500,64,64,64,64 (default) and many combinations with 1024 for buffers and windowssizes, to no avail. I rebooted guest between changes.

So, I continue switching interfaces in the guest... but...

Any advice?
Could it be a bug there (VirtualBox or Virtio driver) or is it a limit of the design?
How to find out?

Open for tests...

By the way, I use virtio and not Intel PRO/1000 because the VirtualBox manual in 6.1 (https://www.virtualbox.org/manual/ch06.html) points to performance improvements. I surely noticed those in downloads....

TIA


Some notes:
Already seen these:
https://serverfault.com/questions/44777 ... -using-nat

very old:
viewtopic.php?f=1&t=87288
https://www.virtualbox.org/ticket/3400
https://www.virtualbox.org/ticket/2438