BIND is most widely used DNS (Domain Name Server) software. Its name originates as an acronym of Berkeley Internet Name Domain. BIND is also called by it service name i.e. named (or Name Daemon). BIND latest version 9 is available now and distributed under Mozilla Public License (MPL). BIND is developed and maintained by Internet Systems Consortium (ISC).
Almost every Internet connection starts with a DNS lookup. Hostname to IP resolution is necessary before sending an email or browsing a website and BIND is the preferred DNS server for Unix/Linux operating systems.
In this article, we are configuring Primary (Master) and Secondary (Slave) DNS servers using BIND 9 on CentOS 7. This article will let you configure a working DNS server (Master/Slave). To start learning BIND and to build a strong foundation, we recommend you to read DNS and BIND (5th Edition) by O'Reilly Media.
Table of Contents:
- Environment Specifications
- Installing BIND 9 DNS Server on CentOS 7
- Configure Primary (Master) DNS Server on CentOS 7
- Configure Secondary (Slave) DNS Server on CentOS 7
Environment Specifications:
We are using two CentOS 7 virtual machines in this article.
Primary (Master) DNS Server:
- CPU - 3.4 Ghz (1 Core)
- Memory - 1 GB
- Storage - 20 GB
- Hostname - dns-01.example.com
- IP Address - 192.168.116.4 /24
- Operating System – CentOS 7.6
Secondary (Slave) DNS Server:
- CPU - 3.4 Ghz (1 Core)
- Memory - 1 GB
- Storage - 20 GB
- Hostname - dns-02.example.com
- IP Address - 192.168.116.5 /24
- Operating System – CentOS 7.6
Installing BIND 9 DNS Server on CentOS 7:
Connect with dns-01.example.com using ssh as root user.
BIND 9 is available through CentOS 7 official yum repository. Therefore, we can easily install it using yum command.
# yum install -y bind bind-utils
BIND 9 has been installed on CentOS 7 server.
Configure Primary (Master) DNS Server on CentOS 7:
By default named.service run on localhost. Since, we are configuring an authoritative DNS server for our Domain, therefore, we need to configure this service to run on the interface that was connected with our network.
# vi /etc/named.conf
Under options directive set following parameter to allow named.service to run on our network interface.
listen-on port 53 { 127.0.0.1; 192.168.116.4; };
We are also required to enable our named.service to allow client queries. Therefore, find and set following parameter in options directives.
allow-query { localhost; 192.168.116.0/24; };
To keep the named.conf file clean, we are defining our DNS zones in a separate file.
# vi /etc/named.conf.local
and add following directives in this file.
zone "example.com" {
type master;
file "/var/named/example.com";
};
zone "116.168.192.in-addr.arpa" {
type master;
file "/var/named/116.168.192.in-addr.arpa";
};
We have defined two DNS zones here, one is a Forward DNS zone and the other is Reverse DNS zone.
Include our named.conf.local file in the default named.conf file, so it will be called at the time of service startup.
# echo 'include "/etc/named.conf.local";' >> /etc/named.conf
Configure forward zone for our Domain.
# vi /var/named/example.com
and add following settings therein.
$TTL 1h
@ IN SOA example.com. root.example.com. (
2019080901 ; Serial YYYYMMDDnn
24h ; Refresh
2h ; Retry
28d ; Expire
2d ) ; Minimum TTL
;Name Servers
@ IN NS dns-01
;Mail Servers
@ IN MX 0 mail-01
;Other Servers
dns-01 IN A 192.168.116.4
mail-01 IN A 192.168.116.6
web-01 IN A 192.168.116.3
;Canonical Names
www IN CNAME web-01
mail IN CNAME mail-01
Check forward zone file for any possible error.
# named-checkzone example.com /var/named/example.com
zone example.com/IN: loaded serial 2019080901
OK
Configure a reverse zone for our Domain.
# vi /var/named/116.168.192.in-addr.arpa
and add following settings therein.
$TTL 1h
@ IN SOA 116.168.192.in-addr.arpa root.example.com. (
2019080901 ; Serial YYYYMMDDnn
24h ; Refresh
2h ; Retry
28d ; Expire
2d ) ; Minimum TTL
;Name Servers
@ IN NS dns-01
;Other Servers
dns-01 IN A 192.168.116.4
;PTR Records
4 IN PTR dns-01
6 IN PTR mail-01
3 IN PTR web-01
Check reverse zone file for any possible errors.
# named-checkzone example.com /var/named/116.168.192.in-addr.arpa
zone example.com/IN: loaded serial 2019080901
OK
Adjust file ownership of zone files.
# chgrp named /var/named/example.com # chgrp named /var/named/116.168.192.in-addr.arpa
Enable and start named.service.
# systemctl enable --now named.service
Created symlink from /etc/systemd/system/multi-user.target.wants/named.service to /usr/lib/systemd/system/named.service.
Allow DNS service in Linux firewall.
# firewall-cmd --permanent --add-service=dns success # firewall-cmd --reload success
Add our Primary (Master) DNS Server to client's resolve.conf.
# nmcli c m ens33 ipv4.dns-search example.com ipv4.dns 192.168.116.4
Restart interface to apply changes.
# nmcli c down ens33 ; nmcli c up ens33
Connection 'ens33' successfully deactivated (D-Bus active path: /org/freedesktop/NetworkManager/ActiveConnection/1)
Connection successfully activated (D-Bus active path: /org/freedesktop/NetworkManager/ActiveConnection/2)
Verify DNS Server settings.
# cat /etc/resolv.conf
# Generated by NetworkManager
search example.com
nameserver 192.168.116.4
Query our Primary (Master) DNS server using dig command.
# dig www.example.com
; <<>> DiG 9.9.4-RedHat-9.9.4-74.el7_6.2 <<>> www.example.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 2020
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 1, ADDITIONAL: 2
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;www.example.com. IN A
;; ANSWER SECTION:
www.example.com. 3600 IN CNAME web-01.example.com.
web-01.example.com. 3600 IN A 192.168.116.3
;; AUTHORITY SECTION:
example.com. 3600 IN NS dns-01.example.com.
;; ADDITIONAL SECTION:
dns-01.example.com. 3600 IN A 192.168.116.4
;; Query time: 1 msec
;; SERVER: 192.168.116.4#53(192.168.116.4)
;; WHEN: Fri Aug 09 23:15:51 PKT 2019
;; MSG SIZE rcvd: 118
Our Primary (Master) DNS Server has been configured on CentOS 7.
Configure Secondary (Slave) DNS Server on CentOS 7:
We have a working Primary (Master) DNS Server. We are now going to add a Secondary (Slave) DNS Server.
Connect with dns-02.example.com using ssh as root user.
Follow the above section "Install BIND 9 DNS Server on CentOS 7" to install BIND 9 packages on our Secondary DNS Server.
Configure named.service settings of our Secondary DNS Server.
# vi /etc/named.conf
Under option directives set following parameters.
listen-on port 53 { 127.0.0.1; 192.168.116.5; };
allow-query { localhost;192.168.116.0/24; };
Just like we did with our Primary DNS Server, we are defining our zones in a separate configuration file.
# vi /etc/named.conf.local
and define following zones therein.
zone "example.com" {
type slave;
masters { 192.168.116.4; };
file "/var/named/example.com";
};
zone "116.168.192.in-addr.arpa" {
type slave;
masters { 192.168.116.4; };
file "/var/named/116.168.192.in-addr.arpa";
};
Include our named.conf.local file in the default named.conf file, so it will call our settings on service startup.
# echo 'include "/etc/named.conf.local";' >> /etc/named.conf
Start and enabled named.service.
# systemctl enable --now named.service
Created symlink from /etc/systemd/system/multi-user.target.wants/named.service to /usr/lib/systemd/system/named.service.
Allow DNS service in Linux firewall.
# firewall-cmd --permanent --add-service=dns success # firewall-cmd --reload success
Set SELinux boolean, so our Secondary DNS server can accept zone transfers and update local zone files.
# setsebool -P named_write_master_zones on
Now, connect to dns-01.example.com and add settings for our Secondary DNS server.
Configure zone transfers by editing named.conf.local file as follows.
# vi /etc/named.conf.local
Add following directives under both zones.
allow-transfer {192.168.116.5; };
also-notify {192.168.116.5; };
Add our Secondary name server record in our forward and reverse zones.
# vi /var/named/example.com
and add Secondary (Slave) DNS server NS and A records as follows:
$TTL 1h
@ IN SOA example.com. root.example.com. (
2019080901 ; Serial YYYYMMDDnn
24h ; Refresh
2h ; Retry
28d ; Expire
2d ) ; Minimum TTL
;Name Servers
@ IN NS dns-01
@ IN NS dns-02
;Mail Servers
@ IN MX 0 mail-01
;Other Servers
dns-01 IN A 192.168.116.4
dns-02 IN A 192.168.116.5
mail-01 IN A 192.168.116.6
web-01 IN A 192.168.116.3
;Canonical Names
www IN CNAME web-01
mail IN CNAME mail-01
Add Secondary name server records in Reverse Zone.
# vi /var/named/116.168.192.in-addr.arpa
and add NS, A and PTR records of our Secondary (Slave) DNS as follows.
$TTL 1h
@ IN SOA 116.168.192.in-addr.arpa root.example.com. (
2019080901 ; Serial YYYYMMDDnn
24h ; Refresh
2h ; Retry
28d ; Expire
2d ) ; Minimum TTL
;Name Servers
@ IN NS dns-01
@ IN NS dns-02
;Other Servers
dns-01 IN A 192.168.116.4
dns-02 IN A 192.168.116.5
;PTR Records
4 IN PTR dns-01
5 IN PTR dns-02
6 IN PTR mail-01
3 IN PTR web-01
Restart named.service to apply changes.
# systemctl restart named.service
Check /etc/named directory at dns-02.example.com.
# ls /var/named
116.168.192.in-addr.arpa dynamic named.ca named.localhost slaves
data example.com named.empty named.loopback
The zone files are automatically replicating to secondary domain name server.
Now add this Secondary DNS server to client's resolve.conf file.
# nmcli c m ens33 +ipv4.dns 192.168.116.5 # nmcli c down ens33 ; nmcli c up ens33 Connection 'ens33' successfully deactivated (D-Bus active path: /org/freedesktop/NetworkManager/ActiveConnection/1) Connection successfully activated (D-Bus active path: /org/freedesktop/NetworkManager/ActiveConnection/2)
Check resolv.conf contents.
# cat /etc/resolv.conf
# Generated by NetworkManager
search example.com
nameserver 192.168.116.4
nameserver 192.168.116.5
Check Secondary DNS settings by query a hostname.
# dig @192.168.116.5 mail.example.com
; <<>> DiG 9.9.4-RedHat-9.9.4-74.el7_6.2 <<>> @192.168.116.5 mail.example.com
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 21668
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 2, ADDITIONAL: 3
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;mail.example.com. IN A
;; ANSWER SECTION:
mail.example.com. 3600 IN CNAME mail-01.example.com.
mail-01.example.com. 3600 IN A 192.168.116.6
;; AUTHORITY SECTION:
example.com. 3600 IN NS dns-02.example.com.
example.com. 3600 IN NS dns-01.example.com.
;; ADDITIONAL SECTION:
dns-01.example.com. 3600 IN A 192.168.116.4
dns-02.example.com. 3600 IN A 192.168.116.5
;; Query time: 2 msec
;; SERVER: 192.168.116.5#53(192.168.116.5)
;; WHEN: Sat Aug 10 13:09:59 PKT 2019
;; MSG SIZE rcvd: 157
Our Secondary (Slave) DNS Server has been configured and working fine.
We have successfully configured authoritative DNS server using BIND 9 on CentOS 7.
