How to set up Proxmox on Virtualbox for virtual networking?

Question

virtual box

There is a virtual network:
1. Host machine (on which Virtualbox itself is running) 2.
Debian on VirtualBox (with Proxmox installed on it)
3. Windows 7 on VirtualBox
two networks, virtual and seemingly physical (well, at least Proxmox thinks so)
1. vmbr
2. enp0s3
I tried it in different ways, I didn’t find it on the Internet (I’m not sure that this is even possible).
For example, I tried to specify in this way:
1. On both vmbr and enp0s3 networks, I specified the address of the machine "Debian on VirtualBox" as the ip address.
2. In the vmbr network settings, I indicated to refer to the enp0s3 network
But I don’t know which gateway to specify (and whether it is necessary) :(
In general, after such manipulations, I can’t reach the Proxmox admin panel, I can’t ping anyone :(

Answer 1

What is the point, I did not understand, but until I added a second network card, the ping did not go. Apparently, Proxmox needs one of the network cards to communicate between its virtual machines. And the second one is for communicating the Proxmox server with the outside world, but this is not accurate :)

Answer 2

and what for twist everything in virtualbox just