CertiGuide to Security+  9  Chapter 3:  Infrastructure Security (Domain 3.0; 20%)       9  3.3  Security Topologies            9  3.3.1  Security Zones

3.3.1  Security Zones 1 2 3 3.3.1.2  Intranet

The DMZ, or Demilitarized Zone, on a network is “that portion of a company’s network which sits between the Internet and an internal network’s line of defense, usually some combination of firewalls and bastion hosts”³²⁷. Firewalls were described earlier in this section. Bastion hosts are gateways between inside and outside networks, designed to defend the internal network from attacks aimed at it from outside.

Much like in the non-computerized world, a network DMZ, sometimes called a “perimeter network,” is a “neutral zone” that attempts to keep external users and the internal network apart. It is strongly advised that there be an external firewall (or at least a well-configured filtering router) between the DMZ and the Internet as well, for protection of the DMZ, although that is not required for that portion of the network to be considered a DMZ.

Usually a DMZ is a separate subnet from your internal network, to minimize opportunities for compromises due to traffic sniffing. While, logically speaking, a DMZ is an intermediate area “between” your internal network and the Internet, a network configuration supporting a DMZ is sometimes implemented by using a single router with three port connections (Internet, DMZ and internal network) and good filtering rules between them.

Figure 37: A router of sufficient recourses can handle multiple ports.

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327. “DMZ”, http://www.webopedia.com

3.3.1  Security Zones 1 2 3 3.3.1.2  Intranet

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