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Preface
You may not know much about the Domain Name
Systemyetbut whenever you use the Internet, you use
DNS. Every time you send electronic mail or surf the Web, you rely on
the Domain Name System.
You see, while you, as a human being, prefer to remember the
names
of computers, computers like to address each other by number. On an
internet, that number is 32 bits long, or between zero and four
billion or so.[1]
That's easy for a computer to remember because
computers have lots of memory ideal for storing numbers, but it
isn't nearly as easy for us humans. Pick 10 phone
numbers out of the phone book at random, and then try to recall them.
Not easy? Now flip to the front of the book and attach random area
codes to the phone numbers. That's about how
difficult it would be to remember 10 arbitrary Internet addresses.
[1] And, with IP Version 6,
it's soon to be a whopping 128 bits long, or between
and a 39-digit decimal number.
This is part of the reason we need the Domain Name System. DNS
handles mapping between
hostnames,
which we humans find convenient, and Internet addresses, which
computers deal with. In fact, DNS is the standard mechanism on the
Internet for advertising and accessing all kinds of information about
hosts, not just addresses. And DNS is used by virtually all
internetworking software, including electronic mail, remote terminal
programs such as telnet, file transfer programs
such as ftp, and web browsers such as Netscape
Navigator and Microsoft Internet Explorer.
Another important feature of DNS is that it makes host information
available all over the Internet. Keeping
information about hosts in a formatted file on a single computer
helps only users on that computer. DNS provides a means of retrieving
information remotely from anywhere on the network.
More than that, DNS lets you distribute the management of host
information among many sites and organizations. You
don't need to submit your data to some central site
or periodically retrieve copies of the
"master" database. You simply make
sure your section, called a zone,
is up to date on your
name servers. Your name servers make your zone's
data available to all the other name servers on the
network.
Because the database is distributed, the system also needs to be able
to locate the data you're looking for by searching a
number of possible locations. The Domain Name System gives name
servers the intelligence to navigate through the database and find
data in any zone.
Of course, DNS does have a few problems. For example, the system
allows more than one name server to store data about a zone for
redundancy's sake, but inconsistencies can crop up
between copies of the zone data.
But the worst problem with DNS is that despite
its widespread use on the Internet, there's really
very little documentation about managing and maintaining it. Most
administrators on the Internet make do with the documentation their
vendors see fit to provide and with whatever they can glean from
following Internet mailing lists and Usenet newsgroups on the
subject.
This lack of documentation
means that the
understanding of an enormously important Internet serviceone
of the linchpins of today's Internetis either
handed down from administrator to administrator like a closely
guarded family recipe or relearned repeatedly by isolated programmers
and engineers. New zone administrators suffer through the same
mistakes made by countless others.
Our aim with this book is to help remedy this situation. We realize
that not all of you have the time or the desire to become DNS
experts. Most of you, after all, have plenty to do besides managing
your zones and name servers: system administration, network
engineering, or software development. It takes an awfully big
institution to devote a whole person to DNS. We'll
try to give you enough information to allow you to do what you need
to do, whether that's running a small zone or
managing a multinational monstrosity, tending a single name server or
shepherding a hundred of them. Read as much as you need to know now,
and come back later if you need to know more.
DNS is a big topicbig enough to require three authors,
anywaybut we've tried to present it as
sensibly and understandably as possible. The first two chapters give
you a good theoretical overview and enough practical information to
get by, and later chapters fill in the nitty-gritty details. We
provide a roadmap up front to suggest a path through the book
appropriate for your job or interest.
When we talk about
actual
DNS software,
we'll concentrate on the Microsoft DNS Server, which
is a popular implementation of the DNS specs included in Windows
Server 2003 (and in Windows 2000 Server and Windows NT Server 4.0
before that). We've tried to distill our experience
in managing and maintaining zones into this book. (One of our zones,
incidentally, was once one of the largest on the Internet, but that
was a long time ago.)
We hope that this book will help you get acquainted with DNS on
Windows Server 2003 if you're just starting out,
refine your understanding if you're already familiar
with it, and provide valuable insight and experience even if you know
it like the back of your hand.
