Workshop

eceptionist hangs up one line (the red phone) and picks up the outside phone to relay the information on
a different call. As such, there are two different routing domains (the two phone systems) involved.
Though this sounds mysterious, it really isn’t—all it means is that two sets of networks (the red phone
and the outside world’s phone system) are prevented from talking to each other because the router
doesn’t share a common network between the two networks (see Figure 15.1).
Figure 15.1 A typical proxy server setup.
Are there still rules involved as to who may call in or out? Definitely. Similar to a packet-filtering
firewall, proxy servers typically have a default policy of “deny everything but the following,” and you
define what is allowed. For example, let’s say the company executives all reside on network 4 in Figure
15.1. They have ruled that only they may have Internet access, so the only explicit rule that you would
set would be this:
Allow all traffic from network 4 from the “inside” interface of the proxy server.
All other traffic, say from network 3, would be denied.
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