What is a firewall?
A system designed to prevent
unauthorized access to or from a private network. Firewalls
can be implemented in both hardware and software, or a
combination of both. Firewalls are frequently used to
prevent unauthorized Internet users from accessing private
networks connected to the Internet, especially intranets.
All messages entering or leaving the intranet pass through
the firewall, which examines each message and blocks those
that do not meet the specified security criteria. There are
several types of firewall techniques: Packet filter: Looks
at each packet entering or leaving the network and accepts
or rejects it based on user-defined rules. Packet filtering
is fairly effective and transparent to users, but it is
difficult to configure. In addition, it is susceptible to IP
spoofing. Application gateway: Applies security mechanisms
to specific applications, such as FTP and Telnet servers.
This is very effective, but can impose a performance
degradation. Circuit-level gateway: Applies security
mechanisms when a TCP or UDP connection is established. Once
the connection has been made, packets can flow between the
hosts without further checking. Proxy server: Intercepts all
messages entering and leaving the network. The proxy server
effectively hides the true network addresses. In practice,
many firewalls use two or more of these techniques in
concert. A firewall is considered a first line of defense in
protecting private information. For greater security, data
can be encrypted.
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