Say you have one or more KVM guests on Proxmox which have one or more virtual interfaces which subnet is different than the HOST one, and you happen to want to reach those interfaces from within LAN for whatever reason...
To accomplish this we will be creating a simple bash script as well as creating a systemd service to have it executed on boot.
/usr/lib/systemd/scripts/routing_tables.sh
#!/bin/bash
vmID=100