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TCP/IP Tutorial and Technical Overview - IBM Redbooks

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time. The network administrator must examine all logs <strong>and</strong> alarms generated by<br />

the firewall on a regular basis. Otherwise, it is generally not possible to protect<br />

the internal network from outside attacks.<br />

Production server<br />

Client1 Client2<br />

private.organization.com<br />

Secure<br />

network<br />

Figure 22-11 A firewall controls traffic between the secure network <strong>and</strong> the Internet<br />

22.3.2 Components of a firewall system<br />

As mentioned previously, a firewall can be a PC, a midrange, a mainframe, a<br />

UNIX workstation, a router, or combination of these. Depending on the<br />

requirements, a firewall can consist of one or more of the following functional<br />

components:<br />

► Packet-filtering router<br />

► Application-level gateway (proxy)<br />

► Circuit-level gateway<br />

Each of these components has different functions <strong>and</strong> shortcomings. Generally,<br />

in order to build an effective firewall, these components are used together.<br />

796 <strong>TCP</strong>/<strong>IP</strong> <strong>Tutorial</strong> <strong>and</strong> <strong>Technical</strong> <strong>Overview</strong><br />

organization.com<br />

Stop<br />

Untrusted network<br />

Internet

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