When a virtual machine on a Proxmox server, or even the host itself, is displaying symptoms of a dropped network packet that is usually a symptom of a physical network issue.
However, that is not always true. Proxmox makes use of a bridge to allow VM networks to connect to the physical network which gives the VM's direct access to the internet. Without the vmbr interface, no VM can access the physical network and you'd have to put a internal router in place.
Sometimes, there are packets that end up being invalid in some way shape or form and those packets can cause weird behavior with the vmbr drivers. The invalid packets get dropped at the bridge interface itself, which causes valid packets to be droped at the same time. There is an easy fix to this.
$ sudo ebtables -A INPUT -p 8912 -j DROP
$ sudo ebtables -A INPUT -p 88e1 -j DROP
Performing the above command will force the invalid packets to be dropped by the bridge firewall, instead of at the interface allowing valid packets to pass through. (Please note you may not need to use `sudo` if you are logged in as root.)
