A couple weeks ago, I discovered that guest network performance was abysmally slow, copy-pasting files from host to guest (RDP) felt like it took days instead of the (expected) minutes! This delayed the commissioning of a new application, and it bugged me for a bit. Later on, a different guest exhibited the same issue; i.e., I could actually see the images it sent over being (very slowly) downloaded in the browser…
After a bit of Google-ing and experimentation, it appears to be related to a NIC issue (our HP server uses Broadcom) and this Virtual Machine Queues (VMQ) option in Windows Server 2012 R2. It’s weird that it hasn’t already been resolved by Broadcom/Microsoft, but here’s the full Reddit link if you need more details.
Do note however that I tried out the Registry update (BelowTenGigVmqEnabled=1), but it didn’t work in my case. I’m just going to quote from the the Redditor in closing:-
My world is beautiful.