bind9/doc/arm/Bv9ARM.ch01.html

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><DIV
CLASS="chapter"
><H1
><A
NAME="ch01"
>Chapter 1. Introduction </A
></H1
><DIV
CLASS="TOC"
><DL
><DT
><B
>Table of Contents</B
></DT
><DT
>1.1. <A
HREF="Bv9ARM.ch01.html#AEN7"
>Scope of Document</A
></DT
><DT
>1.2. <A
HREF="Bv9ARM.ch01.html#AEN13"
>Organization of This Document</A
></DT
><DT
>1.3. <A
HREF="Bv9ARM.ch01.html#AEN32"
>Conventions Used in This Document</A
></DT
><DT
>1.4. <A
HREF="Bv9ARM.ch01.html#AEN121"
>Discussion of Domain Name System (<SPAN
CLASS="acronym"
>DNS</SPAN
>) Basics and
<SPAN
CLASS="acronym"
>BIND</SPAN
></A
></DT
></DL
></DIV
><P
>The Internet Domain Name System (<SPAN
CLASS="acronym"
>DNS</SPAN
>) consists of the syntax
  to specify the names of entities in the Internet in a hierarchical
  manner, the rules used for delegating authority over names, and the
  system implementation that actually maps names to Internet
  addresses.  <SPAN
CLASS="acronym"
>DNS</SPAN
> data is maintained in a group of distributed
  hierarchical databases.</P
><DIV
CLASS="sect1"
><H1
CLASS="sect1"
><A
NAME="AEN7"
>1.1. Scope of Document</A
></H1
><P
>The Berkeley Internet Name Domain (<SPAN
CLASS="acronym"
>BIND</SPAN
>) implements an
    Internet nameserver for a number of operating systems. This
    document provides basic information about the installation and
    care of the Internet Software Consortium (<SPAN
CLASS="acronym"
>ISC</SPAN
>) <SPAN
CLASS="acronym"
>BIND</SPAN
> version 9
    software package for system administrators.</P
></DIV
><DIV
CLASS="sect1"
><H1
CLASS="sect1"
><A
NAME="AEN13"
>1.2. Organization of This Document</A
></H1
><P
>In this document, <I
CLASS="emphasis"
>Section 1</I
> introduces
    the basic <SPAN
CLASS="acronym"
>DNS</SPAN
> and <SPAN
CLASS="acronym"
>BIND</SPAN
> concepts. <I
CLASS="emphasis"
>Section 2</I
>
    describes resource requirements for running <SPAN
CLASS="acronym"
>BIND</SPAN
> in various
    environments. Information in <I
CLASS="emphasis"
>Section 3</I
> is
    <I
CLASS="emphasis"
>task-oriented</I
> in its presentation and is
    organized functionally, to aid in the process of installing the
    <SPAN
CLASS="acronym"
>BIND</SPAN
> 9 software. The task-oriented section is followed by
    <I
CLASS="emphasis"
>Section 4</I
>, which contains more advanced
    concepts that the system administrator may need for implementing
    certain options. Section 5 describes the <SPAN
CLASS="acronym"
>BIND</SPAN
> 9 lightweight
    resolver.  The contents of <I
CLASS="emphasis"
>Section 6</I
> are
    organized as in a reference manual to aid in the ongoing
    maintenance of the software. <I
CLASS="emphasis"
>Section 7
    </I
>addresses security considerations, and
    <I
CLASS="emphasis"
>Section 8</I
> contains troubleshooting help. The
    main body of the document is followed by several
    <I
CLASS="emphasis"
>Appendices</I
> which contain useful reference
    information, such as a <I
CLASS="emphasis"
>Bibliography</I
> and
    historic information related to <SPAN
CLASS="acronym"
>BIND</SPAN
> and the Domain Name
    System.</P
></DIV
><DIV
CLASS="sect1"
><H1
CLASS="sect1"
><A
NAME="AEN32"
>1.3. Conventions Used in This Document</A
></H1
><P
>In this document, we use the following general typographic
    conventions:</P
><DIV
CLASS="informaltable"
><P
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><TBODY
><TR
><TD
WIDTH="288"
ALIGN="LEFT"
VALIGN="MIDDLE"
>&#13;<P
><I
CLASS="emphasis"
>To
describe:</I
></P
></TD
><TD
WIDTH="252"
ALIGN="LEFT"
VALIGN="MIDDLE"
>&#13;<P
><I
CLASS="emphasis"
>We use the style:</I
></P
></TD
></TR
><TR
><TD
WIDTH="288"
ALIGN="LEFT"
VALIGN="MIDDLE"
>&#13;<P
>a pathname, filename, URL, hostname,
mailing list name, or new term or concept</P
></TD
><TD
WIDTH="252"
ALIGN="LEFT"
VALIGN="MIDDLE"
><P
><TT
CLASS="filename"
>Italic</TT
></P
></TD
></TR
><TR
><TD
WIDTH="288"
ALIGN="LEFT"
VALIGN="MIDDLE"
><P
>literal user
input</P
></TD
><TD
WIDTH="252"
ALIGN="LEFT"
VALIGN="MIDDLE"
><P
><TT
CLASS="userinput"
><B
>Fixed Width Bold</B
></TT
></P
></TD
></TR
><TR
><TD
WIDTH="288"
ALIGN="LEFT"
VALIGN="MIDDLE"
><P
>variable user
input</P
></TD
><TD
WIDTH="252"
ALIGN="LEFT"
VALIGN="MIDDLE"
><P
>[<SPAN
CLASS="optional"
>Fixed Width Italic</SPAN
>]</P
></TD
></TR
><TR
><TD
WIDTH="288"
ALIGN="LEFT"
VALIGN="MIDDLE"
><P
>program output</P
></TD
><TD
WIDTH="252"
ALIGN="LEFT"
VALIGN="MIDDLE"
><P
><TT
CLASS="computeroutput"
>Fixed Width Bold</TT
></P
></TD
></TR
></TBODY
></TABLE
><P
></P
></DIV
><P
>The following conventions are used in descriptions of the
<SPAN
CLASS="acronym"
>BIND</SPAN
> configuration file:<DIV
CLASS="informaltable"
><P
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><TBODY
><TR
><TD
WIDTH="288"
ALIGN="LEFT"
VALIGN="MIDDLE"
><P
><I
CLASS="emphasis"
>To
describe:</I
></P
></TD
><TD
WIDTH="252"
ALIGN="LEFT"
VALIGN="MIDDLE"
><P
><I
CLASS="emphasis"
>We use the style:</I
></P
></TD
></TR
><TR
><TD
WIDTH="288"
ALIGN="LEFT"
VALIGN="MIDDLE"
><P
>keywords</P
></TD
><TD
WIDTH="252"
ALIGN="LEFT"
VALIGN="MIDDLE"
><P
><TT
CLASS="literal"
>Sans Serif Bold</TT
></P
></TD
></TR
><TR
><TD
WIDTH="288"
ALIGN="LEFT"
VALIGN="MIDDLE"
><P
>variables</P
></TD
><TD
WIDTH="252"
ALIGN="LEFT"
VALIGN="MIDDLE"
><P
><TT
CLASS="varname"
>Sans Serif Italic</TT
></P
></TD
></TR
><TR
><TD
WIDTH="288"
ALIGN="LEFT"
VALIGN="MIDDLE"
><P
>"meta-syntactic"
information (within brackets when optional)</P
></TD
><TD
WIDTH="252"
ALIGN="LEFT"
VALIGN="MIDDLE"
><P
>[<SPAN
CLASS="optional"
>Fixed Width Italic</SPAN
>]</P
></TD
></TR
><TR
><TD
WIDTH="288"
ALIGN="LEFT"
VALIGN="MIDDLE"
><P
>Command line
input</P
></TD
><TD
WIDTH="252"
ALIGN="LEFT"
VALIGN="MIDDLE"
><P
><TT
CLASS="userinput"
><B
>Fixed Width Bold</B
></TT
></P
></TD
></TR
><TR
><TD
WIDTH="288"
ALIGN="LEFT"
VALIGN="MIDDLE"
><P
>Program output</P
></TD
><TD
WIDTH="252"
ALIGN="LEFT"
VALIGN="MIDDLE"
><P
><TT
CLASS="computeroutput"
>Fixed Width</TT
></P
></TD
></TR
><TR
><TD
WIDTH="288"
ALIGN="LEFT"
VALIGN="MIDDLE"
><P
>Optional input</P
></TD
><TD
WIDTH="252"
ALIGN="LEFT"
VALIGN="MIDDLE"
><P
>[<SPAN
CLASS="optional"
>Text is enclosed in square brackets</SPAN
>]</P
></TD
></TR
></TBODY
></TABLE
><P
></P
></DIV
></P
></DIV
><DIV
CLASS="sect1"
><H1
CLASS="sect1"
><A
NAME="AEN121"
>1.4. Discussion of Domain Name System (<SPAN
CLASS="acronym"
>DNS</SPAN
>) Basics and
<SPAN
CLASS="acronym"
>BIND</SPAN
></A
></H1
><P
>The purpose of this document is to explain the installation
and basic upkeep of the <SPAN
CLASS="acronym"
>BIND</SPAN
> software package, and we begin by reviewing
the fundamentals of the domain naming system as they relate to <SPAN
CLASS="acronym"
>BIND</SPAN
>.
<SPAN
CLASS="acronym"
>BIND</SPAN
> consists of a <I
CLASS="emphasis"
>nameserver</I
> (or "daemon")
called <B
CLASS="command"
>named</B
> and a <B
CLASS="command"
>resolver</B
> library.
The <SPAN
CLASS="acronym"
>BIND</SPAN
> server runs in the background, servicing queries on a well
known network port. The standard port for the User Datagram Protocol
(UDP) and Transmission Control Protocol (TCP), usually port 53,
is specified in<B
CLASS="command"
> </B
><TT
CLASS="filename"
>/etc/services</TT
>.
The <I
CLASS="emphasis"
>resolver</I
> is a set of routines residing
in a system library that provides the interface that programs can
use to access the domain name services.</P
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="AEN136"
>1.4.1. Nameservers</A
></H2
><P
>A nameserver (NS) is a program that stores information about
named resources and responds to queries from programs called <I
CLASS="emphasis"
>resolvers</I
> which
act as client processes. The basic function of an NS is to provide
information about network objects by answering queries.</P
><P
>With the nameserver, the network can be broken into a hierarchy
of domains. The name space is organized as a tree according to organizational
or administrative boundaries. Each node of the tree, called a domain,
is given a label. The name of the domain is the concatenation of
all the labels of the domains from the root to the current domain.
This is represented in written form as a string of labels listed
from right to left and separated by dots. A label need only be unique
within its domain. The whole name space is partitioned into areas
called <I
CLASS="emphasis"
>zones</I
>, each starting at a domain and
extending down to the leaf domains or to domains where other zones
start. Zones usually represent administrative boundaries. For example,
a domain name for a host at the company <I
CLASS="emphasis"
>Example, Inc.</I
> would
be:</P
><P
><SPAN
CLASS="systemitem"
>ourhost.example.com</SPAN
></P
><P
>where <SPAN
CLASS="systemitem"
>com</SPAN
> is the top level domain to which <SPAN
CLASS="systemitem"
>ourhost.example.com</SPAN
> belongs, <SPAN
CLASS="systemitem"
>example</SPAN
> is
a subdomain of <SPAN
CLASS="systemitem"
>com</SPAN
>, and <SPAN
CLASS="systemitem"
>ourhost</SPAN
> is the
name of the host.</P
><P
>The specifications for the domain nameserver are defined in
the RFC 1034, RFC 1035 and RFC 974. These documents can be found
in
<TT
CLASS="filename"
>/usr/src/etc/named/doc</TT
> in 4.4BSD or are available
via File Transfer Protocol (FTP) from
<A
HREF="ftp://www.isi.edu/in-notes/"
TARGET="_top"
>ftp://www.isi.edu/in-notes/</A
> or via the Web at <A
HREF="http://www.ietf.org/rfc/"
TARGET="_top"
>http://www.ietf.org/rfc/</A
>.
(See Appendix C for complete information on finding and retrieving
RFCs.) It is also recommended that you read the related man pages: <B
CLASS="command"
>named</B
> and <B
CLASS="command"
>resolver</B
>.</P
></DIV
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="AEN157"
>1.4.2. Types of Zones</A
></H2
><P
>As we stated previously, a zone is a point of delegation in
the <SPAN
CLASS="acronym"
>DNS</SPAN
> tree. A zone consists of those contiguous parts of the domain
tree for which a domain server has complete information and over which
it has authority. It contains all domain names from a certain point
downward in the domain tree except those which are delegated to
other zones. A delegation point has one or more NS records in the
parent zone, which should be matched by equivalent NS records at
the root of the delegated zone.</P
><P
>To properly operate a nameserver, it is important to understand
the difference between a <I
CLASS="emphasis"
>zone</I
> and a <I
CLASS="emphasis"
>domain</I
>.</P
><P
>For instance, consider the <SPAN
CLASS="systemitem"
>example.com</SPAN
> domain
which includes names such as <SPAN
CLASS="systemitem"
>host.aaa.example.com </SPAN
>and <SPAN
CLASS="systemitem"
>host.bbb.example.com</SPAN
> even
though the <SPAN
CLASS="systemitem"
>example.com</SPAN
> zone includes only delegations
for the <SPAN
CLASS="systemitem"
>aaa.example.com</SPAN
> and <SPAN
CLASS="systemitem"
>bbb.example.com</SPAN
> zones.
A zone can map exactly to a single domain, but could also include
only part of a domain, the rest of which could be delegated to other
nameservers. Every name in the <SPAN
CLASS="acronym"
>DNS</SPAN
> tree is a <I
CLASS="emphasis"
>domain</I
>,
even if it is <I
CLASS="emphasis"
>terminal</I
>, that is, has no <I
CLASS="emphasis"
>subdomains</I
>.
Every subdomain is a domain and every domain except the root is
also a subdomain. The terminology is not intuitive and we suggest
that you read RFCs 1033, 1034 and 1035 to gain a complete understanding
of this difficult and subtle topic.</P
><P
>Though <SPAN
CLASS="acronym"
>BIND</SPAN
> is a Domain Nameserver, it deals primarily in
terms of zones. The master and slave declarations in the <TT
CLASS="filename"
>named.conf</TT
> file
specify zones, not domains. When you ask some other site if it is willing
to be a slave server for your <I
CLASS="emphasis"
>domain</I
>, you are
actually asking for slave service for some collection of zones.</P
><P
>Each zone will have one <I
CLASS="emphasis"
>primary master</I
> (also
called <I
CLASS="emphasis"
>primary</I
>) server which loads the zone
contents from some local file edited by humans or perhaps generated
mechanically from some other local file which is edited by humans.
There there will be some number of <I
CLASS="emphasis"
>slave</I
> (also
called <I
CLASS="emphasis"
>secondary) </I
>servers, which load the zone
contents using the <SPAN
CLASS="acronym"
>DNS</SPAN
> protocol (that is, the secondary servers
will contact the primary and fetch the zone data using TCP). This
set of servers &#8212; the primary and all of its secondaries &#8212; should be
listed in the NS records in the parent zone and will constitute a <I
CLASS="emphasis"
>delegation</I
>.
This set of servers must also be listed in the zone file itself,
usually under the <B
CLASS="command"
>@</B
> name which indicates the <I
CLASS="emphasis"
>top
level</I
> or <I
CLASS="emphasis"
>root</I
> of the current zone.
You can list servers in the zone's top-level <B
CLASS="command"
>@</B
> NS
records that are not in the parent's NS delegation, but you cannot
list servers in the parent's delegation that are not present in
the zone's <B
CLASS="command"
>@</B
>.</P
><P
>Any servers listed in the NS records must be configured as <I
CLASS="emphasis"
>authoritative</I
> for
the zone. A server is authoritative for a zone when it has been
configured to answer questions for that zone with authority, which
it does by setting the "authoritative answer" (AA) bit in reply
packets. A server may be authoritative for more than one zone. The
authoritative data for a zone is composed of all of the Resource
Records (RRs) &#8212; the data associated with names in a tree-structured
name space &#8212; attached to all of the nodes from the top node of the
zone down to leaf nodes or nodes above cuts around the bottom edge
of the zone.</P
><P
>Adding a zone as a type master or type slave will tell the
server to answer questions for the zone authoritatively. If the
server is able to load the zone into memory without any errors it
will set the AA bit when it replies to queries for the zone. See
RFCs 1034 and 1035 for more information about the AA bit.</P
></DIV
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="AEN194"
>1.4.3. Servers</A
></H2
><P
>A <SPAN
CLASS="acronym"
>DNS</SPAN
> server can be master for some zones and slave for others
or can be only a master, or only a slave, or can serve no zones
and just answer queries via its <I
CLASS="emphasis"
>cache</I
>. Master
servers are often also called <I
CLASS="emphasis"
>primaries</I
> and
slave servers are often also called <I
CLASS="emphasis"
>secondaries</I
>.
Both master/primary and slave/secondary servers are authoritative
for a zone.</P
><P
>All servers keep data in their cache until the data expires,
based on a Time To Live (TTL) field which is maintained for all
resource records.</P
><DIV
CLASS="sect3"
><H3
CLASS="sect3"
><A
NAME="AEN202"
>1.4.3.1. Master Server</A
></H3
><P
>The <I
CLASS="emphasis"
>primary master server</I
> is the ultimate
source of information about a domain. The primary master is an authoritative
server configured to be the source of zone transfer for one or more
secondary servers. The primary master server obtains data for the
zone from a file on disk.</P
></DIV
><DIV
CLASS="sect3"
><H3
CLASS="sect3"
><A
NAME="AEN206"
>1.4.3.2. Slave Server</A
></H3
><P
>A <I
CLASS="emphasis"
>slave server</I
>, also called a <I
CLASS="emphasis"
>secondary
server</I
>, is an authoritative server that uses zone transfers from
the primary master server to retrieve the zone data. Optionally,
the slave server obtains zone data from a cache on disk. Slave servers
provide necessary redundancy. All secondary/slave servers are named
in the NS RRs for the zone.</P
></DIV
><DIV
CLASS="sect3"
><H3
CLASS="sect3"
><A
NAME="AEN211"
>1.4.3.3. Caching Only Server</A
></H3
><P
>Some servers are <I
CLASS="emphasis"
>caching only servers</I
>.
This means that the server caches the information that it receives
and uses it until the data expires. A caching only server is a server
that is not authoritative for any zone. This server services queries
and asks other servers, who have the authority, for the information
it needs.</P
></DIV
><DIV
CLASS="sect3"
><H3
CLASS="sect3"
><A
NAME="AEN215"
>1.4.3.4. Forwarding Server</A
></H3
><P
>Instead of interacting with the nameservers for the root and
other domains, a <I
CLASS="emphasis"
>forwarding server</I
> always forwards
queries it cannot satisfy from its authoritative data or cache to
a fixed list of other servers. The forwarded queries are also known
as <I
CLASS="emphasis"
>recursive queries</I
>, the same type as a client would
send to a server. There may be one or more servers forwarded to,
and they are queried in turn until the list is exhausted or an answer
is found. A forwarding server is typically used when you do not
wish all the servers at a given site to interact with the rest of
the Internet servers. A typical scenario would involve a number
of internal <SPAN
CLASS="acronym"
>DNS</SPAN
> servers and an Internet firewall. Servers unable
to pass packets through the firewall would forward to the server
that can do it, and that server would query the Internet <SPAN
CLASS="acronym"
>DNS</SPAN
> servers
on the internal server's behalf. An added benefit of using the forwarding
feature is that the central machine develops a much more complete
cache of information that all the workstations can take advantage
of.</P
><P
>There is no prohibition against declaring a server to be a
forwarder even though it has master and/or slave zones as well;
the effect will still be that anything in the local server's cache
or zones will be answered, and anything else will be forwarded using
the forwarders list.</P
></DIV
><DIV
CLASS="sect3"
><H3
CLASS="sect3"
><A
NAME="AEN223"
>1.4.3.5. Stealth Server</A
></H3
><P
>A <I
CLASS="emphasis"
>stealth server</I
> is a server that answers
authoritatively for a zone, but is not listed in that zone's NS
records. Stealth servers can be used as a way to centralize distribution
of a zone, without having to edit the zone on a remote nameserver.
Where the master file for a zone resides on a stealth server in
this way, it is often referred to as a "hidden primary" configuration.
Stealth servers can also be a way to keep a local copy of a zone
for rapid access to the zone's records, even if all "official" nameservers
for the zone are inaccessible.</P
></DIV
></DIV
></DIV
></DIV
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