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This chapter introduces the Domain Name System (DNS), and ENUM, a tele-
phone number mapping system for Internet resources. Readers interested in a
more thorough understanding of the DNS and ENUM can find books on these
topics or a few high-quality free online tutorials. (Unfortunately, many
DNS online tutorials have not been updated for quite some time.) A good
online resource for understanding DNS can be found for example at http://
technet.microsoft.com/default.aspx[1]. For an in-depth study of
DNS we recommend the authoritative online tutorial available from the IETF
and further reading of the references provided there [2].

Introduction

Readers will easily recall how their web browser finds the IP address for a web
site. For example, when you enter for the first time (the web site address and
the web pages were not yet cached by the browser) the web site name:

ietf.org

the browser will first display (usually in the bottom-left panel) a message
such as:

Finding site: ietf.org

DNS and ENUM

CHAPTER

4