How can firewall settings on the server host machine lead to a "Network is unreachable" error, and how should they be configured?

Firewalls (e.g., Windows Defender Firewall, iptables on Linux, or security groups in cloud environments) can block incoming connections to the Minecraft server's port (default 25565). To resolve this, you must create an inbound rule that allows TCP traffic on the specific port your Minecraft server is running on. For Windows, go to Windows Defender Firewall with Advanced Security -> Inbound Rules -> New Rule, select Port, TCP, specific port (25565), and allow the connection.