Just as the data in your name server provides mapping of names to Internet addresses, the IN-ADDR.ARPA zone provides mapping of addresses to names. However, in the structure of the IN-ADDR.ARPA zone, the IP address appears in reverse. For example, an IP address of 100.20.30.4 in the san-jose. novell.com domain would be 4.30.20.100.in-addr.arpa in the IN-ADDR.ARPA subdomain.