If we want to have separate zones for both the Internet and intranet, we have to keep them on two separate computers (since they have the same domain name). The aim of dual DNS is to run the primary name server of the company.com domain of both the Internet and intranet on just one computer if it is a question of money. While in big companies many different servers are run on the intranet, which enables the operation of separate name servers, small companies would often not wish to install another computer just to run the name server.

But how does a dual DNS work? Two name servers are run on the firewall (two processes). Each of them is run on a different port. The following figure shows the Internet name server being run on port 7053, while the intranet name server is run on port 8053:

Figure 10.5: Dual DNS

It is improbable that the usual client would use a port other than port 53, since they would not be aware of the existence of ports 7053 and 8053.

A DNS proxy is run on the...