Firewalls carefully analyze incoming traffic based on pre-established rules and filter traffic coming from unsecured or suspicious sources to prevent attacks.

 

Firewalls guard traffic at a computer’s entry point, called ports, which is where information is exchanged with external devices. 

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Think of IP addresses as houses, and port numbers as rooms within the house. Only trusted people (source addresses) are allowed to enter the house (destination address) at all—then it’s further filtered so that people within the house are only allowed to access certain rooms (destination ports), depending on if they're the owner, a child, or a guest.

 

The owner is allowed to any room (any port), while children and guests are allowed into a certain set of rooms (specific ports).