Lecture 19: Network Security

Application Gateways

In this configuration, the only system which has access to the outside Internet is the bastion host. In turn, the systems on the internal LAN (nowadays often referred to as the "Intranet") can only contact the bastion host, or gateway. Both of these conditions are configured using IP address-based packet filtering in the routers.

If users connected to the internal LANs wish to use the services of the outside Internet, they can (eg) telnet to the gateway, and then use standard tools running on it to access the rest of the Internet.

An example of such a structure is provided by an electronic mail gateway. Typically, a mail gateway in the DMZ receives messages addressed to an alias address, such as:

Phil.Scott@latrobe.edu.au

and delivers the message to an appropriate system and person within the organisation. The MX type in the DNS is used to support such mail gateway systems.

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