A firewall

A firewall is often a hardware device that has rules which traffic can go out and what to do with incoming traffic.

Physical device firewall management is often done by a dedicated networking person.

Online services like AWS have traffic or firewall rules specify which traffic can be allowed to a virtual host.

Firewall rules management is a big responsibility, because misconfiguration of firewall rules may either block network traffic that needs to traverse firewall boundaries, or it can allow traffic that needs to be stopped.

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