About DNS
DNS, stands for Domain Name System, translates hostnames or URLs into IP addresses. For example, if we typewww.unixmen.com in browser, the DNS server translates the domain name into its associated ip address. Since the IP addresses are hard to remember all time, DNS servers are used to translate the hostnames like www.unixmen.com to 173.xxx.xx.xxx. So it makes easy to remember the domain names instead of its IP address.
In this tutorial, we will see how to setup and configure DNS server on Ubuntu 15.10 server. Also, the same method will work on Debian and its derivatives.
Setup DNS Server In Ubuntu 15.10
Scenario
For the purpose of this tutorial, I will be using three systems. One will be acting as Master DNS server, the second system will be acting as Secondary DNS, and the third will be our DNS client. Here are my three systems details.
Primary (Master) DNS Server Details:
Operating System : Ubuntu 15.10 64bit minimal server Hostname : masterdns.unixmen.local IP Address : 192.168.1.101/24
Secondary (Slave) DNS Server Details:
Operating System : Ubuntu 15.10 64bit minimal server Hostname : secondarydns.unixmen.local IP Address : 192.168.1.102/24
Client Details:
Operating System : Ubuntu 14.04 desktop Hostname : client.unixmen.local IP Address : 192.168.1.103/24
Setup Caching Server
In this configuration, BIND9 will find the answer to name queries and remember the answer for the next query. This can be useful for a slow internet connection. By caching DNS queries, you will reduce bandwidth and (more importantly) latency.
The default configuration is setup to act as a caching server. All that is required is simply adding the IP Addresses of your ISP’s DNS servers. Caching server is opt for low Internet connection.
Install bind9 packages using command:
sudo apt-get install bind9 bind9utils bind9-doc
Then edit /etc/bind/named.conf.options file,
sudo vi /etc/bind/named.conf.options
Simply uncomment and edit the following in /etc/bind/named.conf.options:
forwarders {
8.8.8.8;
};
Restart bind9 service.
sudo systemctl restart bind9
Test Caching Server
Run the following command to test it.
dig -x 127.0.0.1
Sample output:
; <<>> DiG 9.9.5-11ubuntu1-Ubuntu <<>> -x 127.0.0.1 ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 60612 ;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 1, ADDITIONAL: 3 ;; OPT PSEUDOSECTION: ; EDNS: version: 0, flags:; udp: 4096 ;; QUESTION SECTION: ;1.0.0.127.in-addr.arpa. IN PTR ;; ANSWER SECTION: 1.0.0.127.in-addr.arpa. 604800 IN PTR localhost. ;; AUTHORITY SECTION: 127.in-addr.arpa. 604800 IN NS localhost. ;; ADDITIONAL SECTION: localhost. 604800 IN A 127.0.0.1 localhost. 604800 IN AAAA ::1 ;; Query time: 4 msec ;; SERVER: 192.168.1.101#53(192.168.1.101) ;; WHEN: Mon Nov 23 17:48:36 IST 2015 ;; MSG SIZE rcvd: 132
Setup Primary (Master) DNS Server
You can use the same server for both Primary and Caching server.
Install bind9 packages on your server if not installed.
sudo apt-get install bind9 bind9utils bind9-doc
1. Configure Master DNS Server
DNS configuration files are stored in /etc/bind directory. Primary configuration file is /etc/bind/namd.conf.
Edit ‘/etc/bind/named.conf’ file.
sudo vi /etc/bind/named.conf
Make sure it contains the following lines. If not, add them.
include "/etc/bind/named.conf.options"; include "/etc/bind/named.conf.local"; include "/etc/bind/named.conf.default-zones";
Save and close the file.
Then, edit named.conf.local,
sudo vi /etc/bind/named.conf.local
Add the following lines:
zone "unixmen.local" {
type master;
file "/etc/bind/forward.unixmen";
allow-transfer { 192.168.1.102; };
also-notify { 192.168.1.102; };
};
zone "1.168.192.in-addr.arpa" {
type master;
file "/etc/bind/reverse.unixmen";
allow-transfer { 192.168.1.102; };
also-notify { 192.168.1.102; };
};
Here,
- forward.unixmen – Forward zone file
- reverse.unixmen – Reverse zone file
- 192.168.1.102 – Slave DNS server IP address
2. Create Zone files
Create forward and reverse zone files which we defiend in the ‘/etc/bind/named.conf.local’ file.
2.1 Create Forward Zone
Create Forward Zone file name forward.unixmen in /etc/bind/zones,
sudo vi /etc/bind/forward.unixmen
Add the following lines:
$TTL 86400 @ IN SOA masterdns.unixmen.local. root.unixmen.local. ( 2011071001 ;Serial 3600 ;Refresh 1800 ;Retry 604800 ;Expire 86400 ;Minimum TTL ) @ IN NS masterdns.unixmen.local. @ IN NS secondarydns.unixmen.local. @ IN A 192.168.1.101 @ IN A 192.168.1.102 @ IN A 192.168.1.103 masterdns IN A 192.168.1.101 secondarydns IN A 192.168.1.102 client IN A 192.168.1.103
2.2 Create Reverse Zone
Create Forward Zone file name reverse.unixmen in /etc/bind/zones,
sudo vi /etc/bind/reverse.unixmen
Add the following lines:
$TTL 86400 @ IN SOA masterdns.unixmen.local. root.unixmen.local. ( 2011071002 ;Serial 3600 ;Refresh 1800 ;Retry 604800 ;Expire 86400 ;Minimum TTL ) @ IN NS masterdns.unixmen.local. @ IN NS secondarydns.unixmen.local. @ IN PTR unixmen.local. masterdns IN A 192.168.1.101 secondarydns IN A 192.168.1.102 client IN A 192.168.1.103 101 IN PTR masterdns.unixmen.local. 102 IN PTR secondarydns.unixmen.local. 103 IN PTR client.unixmen.local.
3. Configuring Permissions, Ownership for Bind
Run the following commands one by one:
chmod -R 755 /etc/bind sudo chown -R bind:bind /etc/bindsudo
4. Test DNS configuration and zone files for any syntax errors
Check DNS default configuration file:
sudo named-checkconf /etc/bind/named.conf
sudo named-checkconf /etc/bind/named.conf.local
If it returns nothing, your configuration is valid.
Check Forward zone:
sudo named-checkzone unixmen.local /etc/bind/forward.unixmen
Sample output:
zone unixmen.local/IN: loaded serial 2011071001 OK
Check reverse zone:
sudo named-checkzone unixmen.local /etc/bind/reverse.unixmen
Sample Output:
zone unixmen.local/IN: loaded serial 2011071002 OK
Restart bind9 service.
sudo systemctl restart bind9
Add the DNS Server details in your network interface config file.
sudo vi /etc/network/interfaces
Add the nameserver IP address:
auto enp0s3 iface enp0s3 inet static address 192.168.1.101 netmask 255.255.255.0 network 192.168.1.0 broadcast 192.168.1.255 gateway 192.168.1.1 dns-nameservers 192.168.1.101 dns-search unixmen.local
Reboot your system.
5. Test DNS Server
Method 1:
dig masterdns.unixmen.local
Sample Output:
; <<>> DiG 9.9.5-11ubuntu1-Ubuntu <<>> masterdns.unixmen.local ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 27712 ;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 2 ;; OPT PSEUDOSECTION: ; EDNS: version: 0, flags:; udp: 4096 ;; QUESTION SECTION: ;masterdns.unixmen.local. IN A ;; ANSWER SECTION: masterdns.unixmen.local. 86400 IN A 192.168.1.101 ;; AUTHORITY SECTION: unixmen.local. 86400 IN NS masterdns.unixmen.local. unixmen.local. 86400 IN NS secondarydns.unixmen.local. ;; ADDITIONAL SECTION: secondarydns.unixmen.local. 86400 IN A 192.168.1.102 ;; Query time: 4 msec ;; SERVER: 192.168.1.101#53(192.168.1.101) ;; WHEN: Mon Nov 23 17:55:00 IST 2015 ;; MSG SIZE rcvd: 125
Method 2:
nslookup unixmen.local
Sample Output:
Server: 192.168.1.101 Address: 192.168.1.101#53 Name: unixmen.local Address: 192.168.1.101 Name: unixmen.local Address: 192.168.1.102 Name: unixmen.local Address: 192.168.1.103
Now the Primary DNS server is ready to use.
It is time to configure our Secondary DNS server.
Setup Secondary(Slave) DNS Server
Secondary DNS server is optional, but recommended. If the master DNS server goes down, the Secondary DNS server will take charge and answer the queries. You need an additional server to setup Slave DNS server.
Install bind9 packages using the following command:
sudo apt-get install bind9 bind9utils bind9-doc
1. Configure Slave DNS Server
Edit ‘/etc/bind/named.conf’ file.
sudo vi /etc/bind/named.conf
Make sure it contains the following lines. If not, add them.
include "/etc/bind/named.conf.options"; include "/etc/bind/named.conf.local"; include "/etc/bind/named.conf.default-zones";
Save and close the file.
Then, edit named.conf.local,
sudo vi /etc/bind/named.conf.local
Add the lines as shown in bold:
zone "unixmen.local" {
type slave;
file "/var/cache/bind/forward.unixmen";
masters { 192.168.5.101; };
};
zone "1.168.192.in-addr.arpa" {
type slave;
file "/var/cache/bind/reverse.unixmen";
masters { 192.168.5.101; };
};
Here,
- forward.unixmen – Forward zone file
- reverse.unixmen – Reverse zone file
- 192.168.1.101 – Master DNS server IP address
The zone file must be in /var/cache/bind/ because, by default, AppArmor only allows write access inside it.
3. Configuring Permissions, Ownership for Bind
Run the following commands one by one:
chmod -R 755 /etc/bind sudo chown -R bind:bind /etc/bindsudo
Restart bind9 service.
sudo service bind9 restart
4. Add the DNS Server details
Add the DNS Server details in your network interface config file.
sudo vi /etc/network/interfaces
# This file describes the network interfaces available on your system # and how to activate them. For more information, see interfaces(5). # The loopback network interface auto lo iface lo inet loopback # The primary network interface auto enp0s3 iface enp0s3 inet static address 192.168.1.102 netmask 255.255.255.0 network 192.168.1.0 broadcast 192.168.1.255 gateway 192.168.1.1 dns-nameservers 192.168.1.101 dns-nameservers 192.168.1.102 dns-search home
Save and close the file.
Reboot your system.
5. Test DNS Server
After logging in to your server, run the following commands to check if DNS server is really working or not.
Method 1:
dig masterdns.unixmen.local
Sample Output:
; <<>> DiG 9.9.5-3-Ubuntu <<>> masterdns.unixmen.local ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 20290 ;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 2 ;; OPT PSEUDOSECTION: ; EDNS: version: 0, flags:; udp: 4096 ;; QUESTION SECTION: ;masterdns.unixmen.local. IN A ;; ANSWER SECTION: masterdns.unixmen.local. 86400 IN A 192.168.1.101 ;; AUTHORITY SECTION: unixmen.local. 86400 IN NS masterdns.unixmen.local. unixmen.local. 86400 IN NS secondarydns.unixmen.local. ;; ADDITIONAL SECTION: secondarydns.unixmen.local. 86400 IN A 192.168.1.102 ;; Query time: 5 msec ;; SERVER: 192.168.1.101#53(192.168.1.101) ;; WHEN: Mon Nov 23 18:02:38 IST 2015 ;; MSG SIZE rcvd: 125
Method 2:
dig secondarydns.unixmen.local
Sample Output:
; <<>> DiG 9.9.5-3-Ubuntu <<>> secondarydns.unixmen.local ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 53461 ;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 2 ;; OPT PSEUDOSECTION: ; EDNS: version: 0, flags:; udp: 4096 ;; QUESTION SECTION: ;secondarydns.unixmen.local. IN A ;; ANSWER SECTION: secondarydns.unixmen.local. 86400 IN A 192.168.1.102 ;; AUTHORITY SECTION: unixmen.local. 86400 IN NS masterdns.unixmen.local. unixmen.local. 86400 IN NS secondarydns.unixmen.local. ;; ADDITIONAL SECTION: masterdns.unixmen.local. 86400 IN A 192.168.1.101 ;; Query time: 5 msec ;; SERVER: 192.168.1.101#53(192.168.1.101) ;; WHEN: Mon Nov 23 18:10:02 IST 2015 ;; MSG SIZE rcvd: 125
Method 3:
nslookup unixmen.local
Sample Output:
Server: 192.168.1.101 Address: 192.168.1.101#53 Name: unixmen.local Address: 192.168.1.101 Name: unixmen.local Address: 192.168.1.103 Name: unixmen.local Address: 192.168.1.102
Note: A zone is only transferred if the Serial Number on the Primary DNS server is larger than the one on the Secondary DNS server.
Client Side Configuration
Add the DNS server details in ‘/etc/resolv.conf’ file in all client systems
vi /etc/resolv.conf
# Generated by NetworkManager search unixmen.local nameserver 192.168.1.101 nameserver 192.168.1.102
Restart network service or reboot the system.
Test DNS Server
Now, you can test the DNS server using any one of the following commands:
dig masterdns.unixmen.local
dig secondarydns.unixmen.local
dig client.unixmen.local
nslookup unixmen.local
That’s all about now. The primary and secondary DNS servers are ready to use.
If you want to setup DNS server on RHEL based systems, check the following links.
Cheers!
