The rapid expansion of industrial connectivity has placed the 4G iot gateway at the heart of many critical infrastructures. These devices bridge remote sensors, cloud platforms, and control centres. However, their exposure to public cellular networks also makes them prime targets for VPN-based intrusions. Attackers increasingly exploit misconfigured tunnels, weak authentication, and outdated firmware to breach iot gateway assets. This guide presents a structured, defence-in-depth approach to lock down your industrial iot gateway against such threats, while preserving performance and reliability.