Another solution would be to use ConnectTCP RPC call, which allows to expose a TCP port of a qube to other qubes using xen channels, this does not even require to do networking or having a NetVM.
You can see an example of it being used in this tutorial: URL filtering HTTPS proxy
It’s really practical when you need regular use of a TCP port between qubes, like hosting something on a qube to be used on another. I should write a guide about ConnectTCP because it’s not really intuitive 