How To Configure Slave BIND DNS Server On Ubuntu 20.04

In our previous guide we covered the setup of Master(Primary) DNS Server. Here we’ll learn that how to configure slave bind dns server on Ubuntu 20.04 . As the name defined, slave obtains the data from the master & keeps this data in the zones for particular time & from there response to the DNS queries. So, let’s move towards the installation process.

Setup

Master DNS Server IP: 172.16.10.2
Master domain name:ns1.osradar.local
Slave DNS Server IP:172.16.10.10
Slave domain name:ns2.osradar.local

Step 1: Configure Master DNS Server On Ubuntu 20.04

The configuration procedure of slave DNS server is similar to the Master server. The main difference b/w is that slave gets it’s data from the Master DNS.

Edit the /etc/bind/named.conf.local file on primary server & add the allow-transfer & also-notify commands. Add this to both zones (forward & reverse).

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

##Forward zone
zone "osradar.local" IN { // Domain name

type master; // Primary DNS

file "/etc/bind/forward.osradar.local.db"; // Forward lookup file

allow-update { none; }; // Since this is the primary DNS, it should be none.
allow-transfer { 172.16.10.10; }; //Allow Transfer of zone from the master server

also-notify { 172.16.10.10; }; //Notify slave for zone changes

};

##Reverse zone

zone "10.16.172.in-addr.arpa" IN { //Reverse lookup name, should match your network in reverse order

type master; // Primary DNS

file "/etc/bind/reverse.osradar.local.db"; //Reverse lookup file

allow-update { none; }; //Since this is the primary DNS, it should be none.

allow-transfer { 172.16.10.10; }; //Allow Transfer of zone from the master server

also-notify { 172.16.10.10; }; //Notify slave for zone changes

};

allow-transfer will help you to transfer data from Primary to secondary server.
also-notify helps you to notify the slave when update is available.

And after making these changes, restart the bind services.

sudo systemctl restart bind9

Step 2: Configure Slave DNS Server On Ubuntu 20.04

Install the following packages required for slave DNS server by typing

sudo apt-get install -y bind9 bind9utils bind9-doc dnsutils

Once packages are installed, edit the /etc/bind/named.conf.local file & update the forward & reverse DNS records.

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

##Forward Zone

zone "osradar.local" IN { //Domain name

type slave; //Secondary Slave DNS

file "/var/cache/bind/forward.osradar.local.db"; //Forward Zone Cache file

masters { 172.16.10.2; }; //Master Server IP

};

##Reverse zone

zone "10.16.172.in-addr.arpa" IN { //Reverse lookup name. Should match your network in reverse order

type slave; // Secondary/Slave DNS

file "/var/cache/bind/reverse.osradar.local.db"; //Reverse Zone Cache file

masters { 172.16.10.2; }; //Master Server IP

};

And then restart the DNS services on slave.

sudo systemctl restart bind9

Step 3: Testing Slave DNS Server On Ubuntu 20.04

In order to test the working of slave DNS server, create a client machine on the slave server and hit.

sudo echo "nameserver 172.16.10.10" >> /etc/resolv.conf

Finally use the dig command to verify the DNS.

[email protected]:~# dig www.osradar.local

; <<>> DiG 9.16.1-Ubuntu <<>> www.osradar.local
;; global options: +cmd
;; Got answer:
;; WARNING: .local is reserved for Multicast DNS
;; You are currently testing what happens when an mDNS query is leaked to DNS
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 24401
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
; COOKIE: b1e287dd1d118ad6010000005f8c88233ef562a7063e7a15 (good)
;; QUESTION SECTION:
;www.osradar.local. IN A

;; ANSWER SECTION:
www.osradar.local. 604800 IN A 172.16.10.3

;; Query time: 0 msec
;; SERVER: 172.16.10.10#53(172.16.10.10)
;; WHEN: Sat Nov 18 18:23:31 UTC 2020
;; MSG SIZE rcvd: 100

So, this is how you can configure DNS Slave Server on Ubuntu 20.04