note to self
When an OpnSense is deployed on Proxmox environment where MTU is <1500, it doesn't seem to auto-detect and leaves the OpnSense unreachable over the web-ui.
One of the easiest methods to get around this is to console on to the opnsense and use ifconfig command to set the interface IP temporarily with the required MTU (Ref) > Connect to the web-ui and then put in the custom MTU again under the interface settings.
