vSwitch couple two VMs on Hetzner

[sup98765]

Hello, Dear Community

I want to couple two VMs Proxmox within one robot account on Hetzner.

I have created vSwitch, then on both Proxmox added to /etc/network/interfaces

iface X.4000 inet manual
auto vmbr4000
iface vmbr4000 inet manual
bridge_ports X.4000
bridge_stp off
bridge_fd 0
mtu 1400

where X - it is the primary network interface of each servers

But I don't understand how assign private net to vSwitch. I have wrote to Hetzner support and got answer that to configure vSwitch in that manner I have no need to buy additionals ips/nets