Packet filtering firewall
Located in a router on the external border of a network
Simplest to implement
The router checks a list of rules when it receives an internal or external request
The rules allow and restrict access based on source, destination, type (IP protocol type, TCP, UDP port #)
Ex: Allow all SMTP email to the server --> any IP address can send email to TCP port 25
Ex: Block telnet requests to the server --> all requests to TCP port 23 are blocked
III. Technical security
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