Server system??”On a Linux server, a firewall can be used to block requests to all incoming
ports except those used to provide the specific services offered by that server. It can also
be used to block any requests from addresses known to be particularly abusive or to allow
more services to computers known to be friendly.
Firewall/router system??”Linux is often used as a dedicated firewall, providing a buffer
between a private network and a public network (such as the Internet). Using Linux in
this scenario, you can make the best use of the full range of firewall features in iptables.
Any packet trying to pass through the firewall can be filtered and then allowed to pass,
be dropped, or be redirected in some way. The firewall can even hide (masquerade) the
identity of private computers coming through the firewall to use the Internet.
Firewalls don??™t require fancy graphical interfaces (in fact, dedicated firewalls usually don??™t have X
running at all, although they often serve up Web content to others). In fact, a Linux firewall in a
home or small-office environment might run on a discarded 486 computer. Its footprint can be so
small that it doesn??™t even need a hard disk??”just a bootable floppy or CD that includes (or can
access) the needed configuration information.
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