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

Implementing DNS: A Practical Example

This section shows the files you need to implement DNS for a sample Internet-connected network, based on the examples used in this chapter.

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.

This example assumes the following.

An environment connected to the Internet
Two networks, each with its own domain (doc.com and sales.doc.com) and its own DNS zone
The doc.com domain and zone is the top zone over the sales.doc.com subdomain and zone
Each network has its own network number
Table 5–1 Example Network Domain and Zone Configuration

Name and Zone

Number

doc.com

123.45.6

sales.doc.com

111.22.3

Name and Zone	Number
`doc.com`	`123.45.6`
`sales.doc.com`	`111.22.3`

Each zone has a master and one slave server, and the slave server of sales.doc.com is also the master server of doc.com

Table 5–2 Example Network DNS Servers


Zone	Host Name	Function	Address	CNAME
`doc.com`	`sirius`	master for `doc.com`	`123.45.6.1`	`dnsmaster`
`doc.com`	`deneb`	slave for `doc.com`	`111.22.3.5`	`dnssecond`
`sales.doc.com`	`altair`	`master` for `sales.doc.com`	`111.22.3.4`	`dnssales`
`sales.doc.com`	`altair`	slave for `sales.doc.com`	`123.45.6.1`	`dnsmaster`

Example Configuration Files

The following code examples show configuration files for the three servers in the two networks.

Example 5–1 Example Configuration File for `dnsmastr` Name Server

;
; Sample named.conf file on dnsmastr (sirius) name server
; 
; global options and defaults
;

options {
        directory  "/var/named";
};

; master zone definitions
;
zone "doc.com"  in  {
        type master;
        file "db.doc.com";
};

zone "6.45.123.in-addr.arpa"  in  {
        type master;
        file "db.123.45.6";
};

zone "0.0.127.in-addr.arpa"  in  {
        type master;
        file "db.127.0.0";
};

; slave server definitions
;
zone "sales.doc.com"  in  {
        type slave;
        file "tmp.db.sales";
        masters { 111.22.3.4; };
};

zone "3.22.111.in-addr.arpa"  in  {
        type slave;
        file "tmp.db.111.22.3";
        masters { 111.22.3.4; };
};

; root hints

zone "."  in  {
        type hint;	
        file "named.ca";
};

Example 5–2 Example Configuration File for `dnssales` Name Server

; 
; Sample named.conf file on the dnssales (altair) name server
; 

options {
        directory  "/var/named";
};

zone "sales.doc.com"  in  {
        type master;
        file "db.sales.doc.com";
};

zone "3.22.111.in-addr.arpa"  in  {
        type master;
        file "db.111.22.3";
};

zone "0.0.127.in-addr.arpa"  in  {
        type master;
        file "db.127.0.0";
};

; root hints

zone "."  in  {
        type hint;
        file "named.ca";
};

Example 5–3 Example Configuration File for `dnssecond` Name Server

; 
;S ample named.conf file on the dnssecond (deneb) name server
; 

options {
        directory  "/var/named";
};

zone "doc.com"  in  {
        type slave;
        file "tmp.db.doc.com";
        masters { 123.45.6.1; };
};

zone "6.45.123.in-addr.arpa"  in  {
        type slave;
        file "tmp.db.123.45.6";
        masters { 123.45.6.1; };
};

zone "0.0.127.in-addr.arpa"  in  {
        type master;
        file "db.127.0.0";
};

; root hints

zone "."  in  {
        type hint;
        file "named.ca";
};

Example `resolv.conf` Files

The following code examples show resolv.conf files for the three servers in the two networks. If the host in question is not running in.named, the local host address should not be used as a name server.

Example 5–4 Example `resolv.conf` File for `dnsmastr` Server

;
; /etc/resolv.conf file for dnsmaster (sirius)
;
domain           doc.com
nameserver       0.0.0.0
nameserver       111.22.3.5

Example 5–5 Example `resolv.conf` File for `dnssales` Server

;
; /etc/resolv.conf file for dnssales (altair)
;
domain           sales.doc.com
nameserver       111.22.3.4
nameserver       123.45.6.1

Example 5–6 Example `resolv.conf` File for `dnssecond` Server

;
; /etc/resolv.conf for dnssecond
;
domain           doc.com
nameserver       111.22.3.5
nameserver       123.45.6.1

Example `named.local` File

The following code example shows the named.local file used by the two master servers on the two networks. Both servers have the same file.

Example 5–7 Example `named.local` File for Both Master Servers

$TTL 5h
; SOA rec
0.0.127.in-addr.arpa. IN SOA siriusdoc.com. sysop.centauri.doc.com.(
                          19970331    ; serial number
                          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.
0.0.127.in_addr.arpa   IN  NS   dnssecond.doc.com
1  IN  PTR localhost.

Example `hosts` Files

The following code examples show db.doc and db.sales files for the two master servers on the two networks.

Example 5–8 Example `db.doc` File for `dnsmastr` Server

$TTL 5h
; SOA rec
doc.com. IN SOA sirius.doc.com. sysop.centauri.doc.com. (
                          19970332    ; serial number
                          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  123.45.6.1
rigel                  IN  A  123.45.6.112
antares                IN  A  123.45.6.90
polaris                IN  A  123.45.6.101
procyon                IN  A  123.45.6.79
tauceti                IN  A  123.45.6.69
altair.sales.doc.com.   N  A   111.22.3.4
; aliases
dnsmastr               IN  CNAME   sirius.doc.com.
dnssecond.doc.com      IN  CNAME   deneb.doc.com

Example 5–9 Example `db.sales` File for `dnssales` Server

$TTL 5h
; SOA rec
sales.doc.com.  IN SOA altair.sales.doc.com. sysop.polaris.doc.com. (
                           19970332    ; serial number
                           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
altair                  IN  A  111.22.3.4
localhost               IN  A  127.0.0.1
sirius.doc.com.         IN  A  123.45.6.1
luna                    IN  A  192.168.8.22
phoebus                 IN  A  192.168.8.24
deimos                  IN  A  192.168.8.25
ganymede                IN  A  192.168.8.27
europa                  IN  A  192.168.8.28
callisto                IN  A  192.168.8.29
; 
; aliases
dnssales.sales.doc.com  IN  CNAME    altair.sales.doc.com

Example `hosts.rev` Files

The following code examples show hosts.rev files for the two master servers on the two networks.

Example 5–10 Example `doc.rev` File for `dnsmastr` server

$TTL 5h
; SOA rec
6.45.123.in-addr.arpa.  IN SOA sirius.doc.com. sysop.centauri.doc.com. (
                           19970331    ; serial number
                           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.
;Pointer records for 123.45.6
1                       IN  PTR sirius.doc.com.
112                     IN  PTR rigel.doc.com.
90                      IN  PTR antares.doc.com. 
101                     IN  PTR polaris.doc.com. 
79                      IN  PTR procyon.doc.com.
69                      IN  PTR tauceti.doc.com.

Example 5–11 Example `hosts.rev` File for `dnssales` Server

$TTL 5h
; SOA rec
3.22.111.in-addr.arpa.  IN SOA altair.sales.doc.com. \
sysop.polaris.doc.com.(
                           19970331    ; serial number
                           10800       ; refresh every 3 hours
                           10800       ; retry every 3 hours
                           604800      ; expire after a week
                           86400 )     ; TTL of 1 day
; Name Servers
3.22.111.in-addr.arpa.  IN  NS  altair.sales.doc.com.; \
Pointer records for 111.22.3
22                      IN  PTR  luna
23                      IN  PTR  deneb
24                      IN  PTR  phoebus
25                      IN  PTR  deimos
26                      IN  PTR  altair
27                      IN  PTR  ganymede
28                      IN  PTR  europa
29                      IN  PTR  callisto

Example `named.ca` File

The following code example shows the named.ca file that is stored on each of the two master servers on the two networks. Both servers use identical named.ca files.

Example 5–12 Example `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

Implementing DNS: A Practical Example

Example Configuration Files

Example 5–1 Example Configuration File for dnsmastr Name Server

Example 5–2 Example Configuration File for dnssales Name Server

Example 5–3 Example Configuration File for dnssecond Name Server

Example resolv.conf Files

Example 5–4 Example resolv.conf File for dnsmastr Server

Example 5–5 Example resolv.conf File for dnssales Server

Example 5–6 Example resolv.conf File for dnssecond Server

Example named.local File

Example 5–7 Example named.local File for Both Master Servers

Example hosts Files

Example 5–8 Example db.doc File for dnsmastr Server

Example 5–9 Example db.sales File for dnssales Server

Example hosts.rev Files

Example 5–10 Example doc.rev File for dnsmastr server

Example 5–11 Example hosts.rev File for dnssales Server

Example named.ca File

Example 5–12 Example named.ca File