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System Administration Guide: Naming and Directory Services (DNS, NIS, and LDAP)

DNS Configuration and Data Files

In addition to the in.named daemon, DNS on a name server consists of a boot file called named.conf, a resolver file named resolv.conf, and four types of zone data files.

Names of DNS Data Files

So long as you are internally consistent, you can name the zone data files anything you want. This flexibility can lead to some confusion when working at different sites or referring to different DNS manuals and books.

For example, the file names used in Sun manuals and at most many Solaris sites vary from those used in the book DNS and BIND by Albitz and Liu, O'Reilly & Associates, 1992, and both of those nomenclatures have some differences from that used in the public-domain Name Server Operations Guide for BIND, University of California.

In addition, this manual and other DNS documentation uses generic names that identify a file's main purpose, and specific example names for that file in code record samples. For example, Solaris Naming manuals use the generic name hosts when describing the function and role of that file, and the example names db.doc and db.sales.doc in code samples.

For reference purposes, the following table compares BIND file names from these three sources.

Table 5–4 BIND File Name Examples

Solaris Names 

O'Reilly Names or other names 

U.C. Berkeley Names 

Content and Purpose of File 

/etc/named.conf

/etc/named.conf

/etc/named.conf

The configuration file specifies the type of server it is running on and the zones that it serves as a 'Master', 'Slave', or 'Stub'. It also defines security, logging, and a finer granularity of options applied to zones. 

/etc/resolv.conf

/etc/resolv.conf

/etc/resolv.conf

This file resides on every DNS client (including DNS servers) and designates the servers that the client queries for DNS information. 

named.ca

db.cache

db.root

root.cache

This file establishes the names of root servers and lists their addresses. 

Generic: hosts Examples: db.doc db.sales

Generic: db.domain Examples: db.movie

db.fx

Generic: hosts

Example: ucbhosts

This file contains all the data about the machines in the local zone that the server serves. 

Generic: hosts.rev

Examples: 

doc.rev

Generic: db.ADDR Examples: db.192.249.249 db.192.249.253

hosts.rev

This file specifies a zone in the in-addr.arpa. domain, a special domain that allows reverse (address-to-name) mapping.

named.local

Generic: db.cache Example: db.127.0.0

named.local

This file specifies the address for the local loopback interface, or localhost 

$INCLUDE files

$INCLUDE files

$INCLUDE files

Any file identified by an $INCLUDE() statement in a data file.

Caution – Caution –

The IP addresses and network numbers used in examples and code samples in this manual are for illustration purposes only. Do not use them as shown because they might have been assigned to an actual network or host.

The named.conf File

The BIND 8.2.4 configuration file, /etc/named.conf establishes the server as a master, slave, or cache-only name server. It also specifies the zones over which the server has authority and which data files it should read to get its initial data.

The /etc/named.conf file contains statements that implement the following.

The configuration file is read by in.named when the daemon is started by the server's start up script, /etc/init.d/inetsvc. The configuration file directs in.named either to other servers or to local data files for a specified domain.

named.conf Statements

The named.conf file contains statements and comments. Statements end with a semicolon. Some statements can contain a contain a block of statements. Again, each statement in the block is terminated with a semicolon.

The named.conf file supports the following statements.

Table 5–5 named.conf Statements
aclDefines a named IP address match list used for access control. The address match list designates one or more IP addresses (dotted-decimal notation) or IP prefixes (dotted-decimal notation followed with a slash and the number of bits in the netmask). The named IP address match list must be defined by an acl statement before it can be used elsewhere; no forward references allowed.
includeInserts an include file at the point where the include statement is encountered. Use include to break up the configuration into more easily managed chunks.
keySpecifies a key ID used for authentication and authorization on a particular name server. See the server statement.
logging Specifies the information the server logs and the destination of log messages.
options Controls global server configuration options and sets default values for other statements.
server Sets designated configuration options associated with a remote name server. Selectively applies options on a per-server basis, rather than to all servers.
zone Defines a zone. Selectively applies options on a per-zone basis, rather than to all zones.

Example 5–13 Example Master Configuration File for a master server


options {
         directory "/var/named";
         datasize 2098;
         forward only;
         forwarders {
                  99.11.33.44;
         };
         recursion no;
         transfers-in 10;
         transfers-per-ns 2;
         allow-transfer {
                  127.0.1.1/24;
         };
};

logging {
         category queries { default_syslog; };
};

include "/var/named/abcZones.conf"

// here are the names of the master files
zone "cities.zn" {
         type master;
         file "db.cities.zn";
};

zone "0.0.127.in-addr.arpa." {
         type master;
         file "db.127.cities.zn";
};

zone "168.192.in-addr.arpa" {
         type master;
         file "db.cities.zn.rev";
};

zone "sales.doc.com" {
         type slave;
         file "slave/db.sales.doc";
         masters {
                  192.168.1.151;
         };
};

zone "168.192.in-addr.arpa" {
         type slave;
         file "slave/db.sales.doc.rev";
         masters {
                  192.168.1.151;
         };
};

The named.ca File

The named.ca file establishes the names of root servers and lists their addresses. If your network is connected to the Internet, named.ca lists the Internet name servers; otherwise, it lists the root domain name servers for your local network. The in.named daemon cycles through the list of servers until it contacts one of them. It then obtains from that server the current list of root servers, which it uses to update named.ca.

Setting Up the named.ca File

Root server names are indicated in the NS record and addresses in the A record. You need to add an NS record and an A record for each root server you want to include in the file.

How you obtain or create your named.ca file depends on whether or not your network is connected to the world Internet.

Internet named.ca File

If your network is connected to the Internet, at the present time you obtain your named.ca file from InterNIC registration services through the following.

If you are following the naming conventions used in this manual, you then move named.root to /var/named/named.ca.

Example 5–14 Example Internet named.ca file


;
; formerly NS1.ISI.EDU
.                        3600000    NS   B.ROOT-SERVERS.NET.
B.ROOT-SERVERS.NET.      3600000    A    128.9.0.107
;
; formerly C.PSI.NET
.                        3600000    NS   C.ROOT-SERVERS.NET.
C.ROOT-SERVERS.NET.      3600000    A    192.33.4.12
;
; formerly TERP.UMD.EDU
.                        3600000    NS   D.ROOT-SERVERS.NET.
D.ROOT-SERVERS.NET.      3600000    A    128.8.10.90
;
; formerly NS.NASA.GOV
;.                       3600000    NS   E.ROOT-SERVERS.NET.
 
E.ROOT-SERVERS.NET.      3600000    A    192.203.230.10
;
; formerly NS.ISC.ORG
.                        3600000    NS   F.ROOT-SERVERS.NET.
F.ROOT-SERVERS.NET.      3600000    A    192.5.5.241
;
; formerly NS.NIC.DDN.MIL
.                        3600000    NS   G.ROOT-SERVERS.NET.
G.ROOT-SERVERS.NET.      3600000    A    192.112.36.4
;
; formerly AOS.ARL.ARMY.MIL
.                        3600000    NS   H.ROOT-SERVERS.NET.
H.ROOT-SERVERS.NET.      3600000    A    128.63.2.53
;
; formerly NIC.NORDU.NET
.                        3600000    NS   I.ROOT-SERVERS.NET.
I.ROOT-SERVERS.NET.      3600000    A    192.36.148.17
;
; temporarily housed at NSI (InterNIC)
.                        3600000    NS   J.ROOT-SERVERS.NET.
J.ROOT-SERVERS.NET.      3600000    A    198.41.0.10
;
; temporarily housed at NSI (InterNIC)
.                        3600000    NS   K.ROOT-SERVERS.NET.
K.ROOT-SERVERS.NET.      3600000    A    198.41.0.11
;
; temporarily housed at ISI (IANA)
.                        3600000    NS   L.ROOT-SERVERS.NET.
L.ROOT-SERVERS.NET.      3600000    A    198.32.64.12
;
; temporarily housed at ISI (IANA)
.                        3600000    NS   M.ROOT-SERVERS.NET.
M.ROOT-SERVERS.NET.      3600000    A    198.32.65.12
; End of File

Non-Internet named.ca File

If your network is not connected to the Internet, you create your own named.ca file. To do this, you designate one of your servers to be the root server, then create a named.ca file on every DNS server pointing to that root server.

For example, suppose your domain is named private and you designate the machine ourroot as your non-Internet root server. The ourroot machine has an IP address of 192.1.1.10. Your named.ca files would then contain the line:


ourroot.private.  999999  IN  A  192.1.1.10

Cache files also need an SOA record, NS records for each domain and subdomain, and A records for each server.

For example, suppose that in addition to ourroot you also had DNS name servers called ourmaster and ourslave. The named.ca files on all of your DNS servers would then look like the following.

Example 5–15 Sample named.ca File (Non-Internet)


;
@    IN    SOA  ourroot.private.   hermit.ourroot.private  (    
                 1997071401       ;  serial number (YYYYMMDD##)
                 10800            ;  refresh after 3 hours
                 3600             ;  retry after 1 hour
                 604800           ;  expire after 1 week
                 86400 )          ;  minimum TTL of 1 day
;
ourroot.private.      999999     IN    A    192.1.1.10
;
private.                         IN    NS   ourmaster.private.
1.1.192.in-addr.arpa             IN    NS   ourmaster.private.
 
ourprivate.private.              IN    A    192.1.1.1
;
private.                         IN    NS   ourslave.private.
1.1.192.in-addr.arpa             IN    NS   ourslave.private.
ourslave.private.            IN    A    192.1.1.2

The hosts File

The hosts file contains all the data about the machines in the local zone. The name of this file is specified in the boot file. To avoid confusion with /etc/hosts, name the file something other than hosts, for example, you could name these files using the pattern db.domain. Using that nomenclature, the host files for the doc.com and sales.doc.com domains might be db.doc and db.sales.

Setting Up the hosts File

The hosts file contains all the data about every machine in your zone. If a zone covers more than one domain, all machines in all the domains covered by the zone are listed in the zone's host file. See Setting Up the hosts File.

Note –

The name hosts is a generic name indicating the file's purpose and content. But to avoid confusion with /etc/hosts, you should name this file something other than hosts. If you have more than one zone, each zone must have its own hosts file and each of these zone hosts files must have a unique name. For example, if your DNS domain is divided into doc.com and sales.doc.com zones, you could name one hosts file db.doc and the other sales.db.doc.

There must be a separate, uniquely named, hosts file for each zone. If you have more than one zone, each zone's host file must include information about the master (master and slave) servers of the other zones, as described in Example 5–16.

Example 5–16 Sample hosts File


;
; SOA rec
doc.com.  IN SOA sirius.doc.com. sysop.centauri.doc.com. (
                 1997071401       ;  serial number (YYYYMMDD##)
                      10800       ;  refresh every 3 hours
                      10800       ;  retry every 3 hours
                      604800      ;  expire after a week
                      86400 )     ;  TTL of 1 day
; Name Servers
doc.com.                   IN  NS  sirius.doc.com.
sales.doc.com.             IN  NS  altair.sales.doc.com.
; Addresses
localhost.                 IN  A  127.0.0.1
 
sirius                    IN  A  192.168.6.1
rigel                     IN  A  192.168.6.112
antares                   IN  A  192.168.6.90
polaris                   IN  A  192.168.6.101
procyon                   IN  A  192.168.6.79
tauceti                   IN  A  123.45.6.69
altair.sales.doc.com.     IN  A   111.22.3.4
; aliases
durvasa                   IN  CNAME sirius.doc.com.
dnsmastr                  IN  CNAME sirius.doc.com.
dnssales                  IN  CNAME altair.sales.doc.com.

A hosts file usually contains these elements:

The hosts.rev File

The hosts.rev file specifies a zone in the in-addr.arpa. domain, the special domain that allows reverse (address-to-name) mapping. The name of this file is specified in the boot file.

Setting Up the hosts.rev File

The hosts.rev file sets up inverse mapping.

Note –

The name hosts.rev is a generic name indicating the file's purpose and content. If you have more than one zone, each zone must have its own hosts.rev file and each of these zone hosts.rev files must have a unique name. For example, if your DNS domain is divided into doc.com and sales.doc.com zones, you could name one hosts.rev file doc.rev and the other sales.rev.

Example 5–17 Sample hosts.rev File


; SOA rec
6.45.123.in-addr.arpa.  IN SOA sirius.doc.com. sysop.centauri.doc.com. (
                 1997071401       ;  serial number (YYYYMMDD##)
                      10800       ;  refresh every 3 hours
                      10800       ;  retry every 3 hours
                      604800      ;  expire after a week
                      86400 )     ;  TTL of 1 day
; Name Servers
6.45.123.in-addr.arpa.   IN  NS  sirius.doc.com.
1                        IN  PTR sirius.doc.com.

A hosts.rev file contains the following elements.

(See Resource Record Types for detailed descriptions of these resource record types.)

The named.local File

The named.local file specifies the address for the local loopback interface, or localhost, with the network address 127.0.0.1. The name of this file is specified in the boot file. Like other files, you can give it a name other than the name used in this manual.

Setting Up the named.local File

The named.local file sets up the local loopback interface for your name server.

Example 5–18 Sample named.localFile


; SOA rec
0.0.127.in-addr.arpa. IN SOA sirius.doc.com sysop.centauri.doc.com (
                          1997071401       ;  serial number (YYYYMMDD##)            
                           10800           ;  refresh every 3 hours
                           10800           ;  retry every 3 hours
                           604800          ;  expire after a week
                           86400 )         ;  TTL of 1 day
; Name Servers
0.0.127.in-addr.arpa.      IN  NS     sirius.doc.com
1                          IN  PTR  localhost.

A named.local file contains these elements:

$INCLUDE Files

An include file is any file named in an $INCLUDE() statement in a DNS data file. $INCLUDE files can be used to separate different types of data into multiple files for your convenience.

For example, suppose a data file contained following line:


$INCLUDE /etc/named/data/mailboxes

This line causes the /etc/named/data/mailboxes file to be loaded at that point. In this instance, /etc/named/data/mailboxes is an $INCLUDE file. Use of $INCLUDE files is optional. You can use as many as you wish, or none at all.