"A firewall is a system or group of systems that enforces an
access control policy between two networks. Firewalls can be
configured to protect against unauthenticated logins from external
networks, and to limit access to external networks from systems on
an internal network. All packets enter or exit through the
firewall, where they are filtered by the type, source address,
destination address, and port information contained in each packet.
This filtering is controlled by rules that are setup within the
"Packets are discreet bundles of information that pass through a
network. A packet is made up of the packet body, which contains the
information you want to transmit, and the packet header, which
contains the source and destination address of the packet, along
with other information."
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