MCSA/MCSE Self-Paced Training Kit (Exam 70-270): Installing ...

13-36 Chapter 13 Supporting TCP/IP
F13us13
Because the DNS distributed database is indexed by name and not by IP address, a
reverse lookup query would require an exhaustive search of every domain name. To
solve this problem, in-addr.arpa was created. This special second-level domain follows
the same hierarchical naming scheme as the rest of the domain namespace; however,
it is based on IP addresses, not domain names, as follows:
■ Subdomains are named after the numbers in the dotted-decimal representation of
IP addresses.
■ The order of the IP address octets is reversed.
■ Companies administer subdomains of the in-addr.arpa domain based on their
assigned IP addresses and subnet mask.
For example, Figure 13-12 shows a dotted-decimal representation of the IP address
192.168.16.200. A company that has an assigned IP address range of 192.168.16.0 to
192.168.16.255 with a subnet mask of 255.255.255.0 has authority over the
16.168.192.in-addr.arpa domain.
Figure 13-12 The in-addr.arpa domain is used in reverse lookup queries.
Lesson Review
arpa
In-addr
“ . ”
0 192
255
0 168
255
0 16
255
0 200
255
On the CD At this point, you should view the multimedia presentation “The Name Resolution
Process,” which is available in the Multimedia folder on the CD-ROM accompanying this
book. This presentation will give you a deeper understanding of the name resolution process.
The following questions are intended to reinforce key information presented in this
lesson. If you are unable to answer a question, review the lesson materials and try the
question again. You can find answers to the questions in the “Questions and Answers”
section at the end of this chapter.