5.9. Tunneling
Tunneling is a way of creating a covert channel, that is, a communication path for messages of one type that uses a path actually intended for some other type of message. Tunneling can be used to sneak past firewall restrictions either to get into a network or to get out of a network. Using tunneling to get out of a network might be a reasonable way to behave, but using it to get into a network usually suggests that someone doesn't understand his/her job. The rest of this section discusses these two options to give you an understanding of the benefits and costs of setting up tunneling, and enable you to make a decision about if and when to use it.
Tunneling into a Network
Once a firewall and DMZ has been set up, it becomes harder ...
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