icann.org/tlds/.
Now you should feel very comfortable with the DNS hierarchy when you see a URL such
as www.novell.com.
DNS maps friendly names to IP addresses. It is similar to a phone book, pairing hostnames
and IP addresses much in the same way as people??™s names are paired with their
telephone numbers. The internal structure of that phone book is the DNS hierarchy. Now
that you understand how DNS is structured, let??™s dive into the internals of it.
Zones
The DNS database contains zones. These are called zone files, which contain resource
records (explained in the next section). A DNS zone file is also a database. There are two
standard zone types: forward lookup zones and reverse lookup zones. A forward lookup
zone allows for a resource-name-to-IP-address resolution. This is what we did in looking
up the IP address of www.novell.com.
A reverse lookup zone, if you haven??™t already guessed, does the opposite, which is allowing
for IP-address-to-resource-name resolution. If you only had an IP address, a reverse
CHAPTER 27 Managing Domain Names 554
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