Petrowhisky

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:


1. 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.


2. Application gateway:
-------------------

Applies security mechanisms to specific
applications, such as FTP and Telnet servers. This is very
effective, but can impose a performance degradation.


3. 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.


4. Proxy server:
---------------

Intercepts all messages entering and leaving the
network. The proxy server effectively hides the true
network addresses


Note: 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.

:tea:

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