Enforcing the Ground Rules

Enforcing the Ground Rules

Parents get to enforce ground rules all the time. Imagine that a kid wants to get permission from a parent to go somewhere or play with someone. "Can I go to Billy's house to play?" the kid asks. His parent replies, "No, Billy's dad leaves his R-rated video tapes lying around, and I don't want you and Billy to be tempted to watch them while his parents aren't home. But Billy can come over here to play." The parent knows what's safe and what isn't and enforces the rules.

Now that Fred knows what he does and doesn't want to happen in his network, he can enforce the rules with a firewall. The network engineer configures the firewall with a set of rules that tell it what's legal and what isn't. Then the firewall allows some packets to pass through it and discards others to enforce the rules.

To enforce the rules, the firewall needs to be in the path that is used for forwarding packets to and from the Internet. Figure 18-4 shows one typical topology.