I am running about a dozen various Linux guests under Windows 10 VirtualBox 5.1. On a guest, I have noticed that while upload speed is satisfactory (ca. 300 Mbit/s in bridged mode, that’s about the speed achievable on the host), download speed is terrible (less than 2 Mbit/s).
Guests are configured with NAT networking with network interfaces being virtio-net. There also is one guest configured in bridged mode I am referring to in the previous paragraph.
Host CPU is Core i5 4460. Linuxes are stock Debian 7, 8, 9, Ubuntu 12.04, CentOS 7, 8, both 32-bit and 64-bit editions. Bridged guest is Funtoo Linux with a custom kernel.
I have changed virtio-net to emulated Intel PRO/1000 MT Desktop with no measurable difference.
Best Answer
I came across many posts complaining about network speed on VirtualBox guests but none of the ideas discussed there made any difference in my case.
While fiddling with different settings in VirtualBox I also changed the type of emulated chipset from default PIIX3 to ICH9 et voilà – download speed was suddenly on par with the upload! With bridged networking, the speed on the guest is about the same as on the host. Speed on NAT networked hosts got bumped to about 200 Mbit/s (i.e. more than 10× boost).
I repeated the procedure, going from ICH9 to PIIX3 and vice versa with the same result – effect of the change on networking speed is immense.