DNS

Primary and replica DNS server configuration

0. Specs

---

0.0. The What

A DNS (Domain Name System) server translates human-readable domain names into numerical IP addresses, allowing users to access websites using easy-to-remember names instead of complex numbers. It acts like a phonebook for the internet, directing traffic to the correct locations.

This tutorial describes how to install and configure authoritative DNS servers for a domain on Debian and Ubuntu servers.

0.1. Notes

This setup will include 2 DNS Servers: 1 Primary (Master) and 1 Replica (Slave).

For redundancy and reliability, every domain on the internet should have at least 2 DNS servers. Therefore, if you want to run your own DNS service, you need at least two servers.

For internal networks, it is also a good practice to install a secondary DNS server for redundancy.

While I personally prefer using services like Cloudflare for my domains due to their global network and DDoS protection, you may have reasons to run your own servers.

0.2. The Environment

Example Specifications (Replace with your own values):

• Server OS: Debian 13/12 or Ubuntu 24.04/22.04 Server (for both DNS servers)
• Domain Name: 386387.xyz
• Primary DNS Server: ns1.386387.xyz at 192.168.1.201
• Replica DNS Server: ns2.386387.xyz at 192.168.1.202
• Sample Host Records:
  • filesrv.386387.xyz: 192.168.1.171
  • mail.386387.xyz: 192.168.1.172
  • mailsrv.386387.xyz (CNAME for mail.386387.xyz)
  • MX record pointing to mail.386387.xyz
• DNS Forwarder: Google’s public DNS (8.8.8.8)

This tutorial has been tested with various combinations including Debian 12/13 and Ubuntu 22.04/24.04.

0.3. Sources

• www.linuxtechi.com
• Mastering Ubuntu Server
• https://bind9.readthedocs.io

1. Primary DNS Server Configuration

---

Install BIND9 (the DNS server software):

sudo apt update
sudo apt -y install bind9

Edit the main configuration file to set global options:

sudo nano /etc/bind/named.conf.options

Modify the options block as follows:

options {
   # Cache Directory
   directory "/var/cache/bind";
   # Allow replica to transfer zone files
   allow-transfer { localhost; 192.168.1.202; };
   # Allow queries from any hosts
   allow-query { any; };
   # Use Google DNS as forwarder
   forwarders { 8.8.8.8; };
   # Automatic DNS Security validation
   dnssec-validation auto;
   # Listen on IP4 from all interfaces
   listen-on { any; };
   # Allow recursive queries
   recursion yes;
};

Define the forward and reverse zones by editing the local configuration file:

sudo nano /etc/bind/named.conf.local

Fill as below

// Forward zone
zone "386387.xyz" IN {
   type master;
   file "/etc/bind/forward.386387.xyz";
};

// Reverse zone
zone "1.168.192.in-addr.arpa" IN {
   type master;
   file "/etc/bind/reverse.386387.xyz";
};

Create and populate the forward zone file:

sudo nano /etc/bind/forward.386387.xyz

Add the following content:

$TTL 1D
@ IN SOA ns1.386387.xyz. hostmaster.386387.xyz. (
   2025111001 ; serial
   8H         ; refresh
   4H         ; retry
   4W         ; expire
   1D         ; minimum TTL
)

; Name Servers for the domain
@               IN      NS      ns1.386387.xyz.
@               IN      NS      ns2.386387.xyz.

; Mail Exchange record
@               IN      MX 10   mail.386387.xyz.

; A Records for Hosts
ns1             IN      A       192.168.1.201
ns2             IN      A       192.168.1.202
filesrv         IN      A       192.168.1.171
mail            IN      A       192.168.1.172

; CNAME Record (Alias)
mailsrv         IN      CNAME   mail.386387.xyz.

Create and populate the reverse zone file:

sudo nano /etc/bind/reverse.386387.xyz

Add the following content:

$TTL 1D
@    IN   SOA    ns1.386387.xyz. hostmaster.386387.xyz. (
   2025111001 ; Serial
   8H         ; Refresh
   4H         ; Retry
   4W         ; Expire
   1D         ; Minimum TTL
)

; Name Servers
@    IN    NS     ns1.386387.xyz.
@    IN    NS     ns2.386387.xyz.
ns1  IN    A      192.168.1.201
ns2  IN    A      192.168.1.202

; PTR Records (IP address to HostName)
201  IN    PTR    ns1.386387.xyz.
202  IN    PTR    ns2.386387.xyz.
171  IN    PTR    filesrv.386387.xyz.
172  IN    PTR    mail.386387.xyz.

Validate all configuration files for syntax errors:

sudo named-checkconf /etc/bind/named.conf.options
sudo named-checkconf /etc/bind/named.conf.local
sudo named-checkzone 386387.xyz /etc/bind/forward.386387.xyz
sudo named-checkzone 386387.xyz /etc/bind/reverse.386387.xyz

2. Replica DNS Server Configuration

---

Install BIND9 on the replica server:

sudo apt update
sudo apt -y install bind9

Edit the main configuration file:

sudo nano /etc/bind/named.conf.options

Use the same configuration as the primary server, but without the allow-transfer directive:

options {
   # Cache Directory
   directory "/var/cache/bind";
   # Allow queries from any hosts
   allow-query { any; };
   # Use Google DNS as forwarder
   forwarders { 8.8.8.8; };
   # Automatic DNS Security validation
   dnssec-validation auto;
   # Listen on IP4 from all interfaces
   listen-on { any; };
   # Allow recursive queries
   recursion yes;
};

Configure the replica zones to sync from the primary server:

sudo nano /etc/bind/named.conf.local

Fill as below

zone "386387.xyz" IN {
   type slave;
   masters { 192.168.1.201; };
   file "/var/lib/bind/forward.386387.xyz";
};
zone "1.168.192.in-addr.arpa" IN {
   type slave;
   masters { 192.168.1.201; };
   file "/var/lib/bind/reverse.386387.xyz";
};

Note that the zone files are located in /var/lib/bind/ and will be automatically populated via zone transfers from the primary server.

Validate the configuration files:

sudo named-checkconf /etc/bind/named.conf.options
sudo named-checkconf /etc/bind/named.conf.local

3. Final Touch

---

3.1. Start the DNS Services

Restart BIND9 on both servers to apply the configuration:

sudo systemctl restart bind9

3.2. Test the DNS Servers

Your name servers should now be operational. You can test them using the dig command from any host on the network:

Test forward lookup (hostname to IP):

dig @192.168.1.201 mail.386387.xyz
dig @192.168.1.202 filesrv.386387.xyz

Test reverse lookup (IP to hostname):

dig @192.168.1.201 -x 192.168.1.171
dig @192.168.1.202 -x 192.168.1.172

Test zone transfer (should only work from replica to primary):

dig @192.168.1.201 386387.xyz AXFR

3.3. Important Notes

Zone File Updates:

• When you modify a zone file on the primary server, you must increment the serial number (the first number in the SOA record) for changes to propagate to the replica server.
• A common format is YYYYMMDDNN (e.g., 2025111001 for the first change on Nov 10, 2025).

Client Configuration:

• To use your new DNS servers, update the DNS settings on your client machines to point to 192.168.1.201 and 192.168.1.202.
• You can also configure the DNS servers themselves to use each other as primary resolvers by editing /etc/resolv.conf.