So I'm using Mosh with a NAT'ed VirtualBox. I needed to forward UDP ports 60000–61000; however, VirtualBox does not allow range forwarding so I needed to do some cmd line magic. Hopefully this helps someone else. From the bash prompt: for i in {60000–61000}; do VBoxManage modifyvm "Ubuntu" --natpf1 "mosh-$i,udp,,$i,,$i"; done