I added a network card to my Proxmox host. I "attached" to it a virtual switch as well for my internal VMs, but it seems that there is some problem with it:
root@pve:~# ifconfig
enp3s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether 00:18:f3:xx:xx:xx txqueuelen 1000...