Configure BIND Slave DNS Server on Debian 11 | Debian 10

DNS servers can be set to perform master or slave functions. In our previous guide, we chewed over how to configure a BIND primary DNS server on Debian 11 | Debian 10. In this guide, we will be walking through how to configure Slave BIND DNS Server on Debian 11 | Debian 10. A slave DNS server receives a copy of data from the master/primary DNS server using the zone transfer method. In this method, zone data is kept in a cache for a given time and is used to serve DNS queries.

Our Environment Setup

In this guide, I will be using a master DNS server whose IP is 192.168.1.12 with the domain name ns1.computingforgeeks.local.

We will set up a secondary server with IP 192.168.1.10. and ns2.computingforgeeks.local as the domain name.

Step 1: Configure BIND Master DNS Server

For this setup (Master-slave) we need to configure the master DNS server and enable zone transfer to the secondary server (ns2.computingforgeeks.local). We first need to edit the /etc/named.conf.local on the primary server (ns1.computingforgeeks.local)

We have a dedicated guide on Master Bind DNS Setup: Configure Master BIND DNS Server on Debian

Install vim or nano editor on Debian 10/Debian 11 with the command:

sudo apt install nano vim 

Then use it to edit the files:

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

In the file, we need to add allow transfer and also-notify parameters as shown below.

##On the Forward zone

zone "computingforgeeks.local" IN { // Domain name
    
      type master; // Primary DNS

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

    allow-update { none; }; // Since this is the primary DNS, it should be none.
     allow-transfer  { 192.168.1.10; }; //Allow Transfer of zone from the master server

     also-notify { 192.168.1.10; }; //Notify slave for zone changes

};

##On the 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.computingforgeeks.local.db"; //Reverse lookup file

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

     allow-transfer  { 192.168.1.10; }; //Allow Transfer of zone from the master server

     also-notify { 192.168.1.10; }; //Notify slave for zone changes

};

The added parameters:

• allow-tranfer-allows the transfer of zone files from the master slave DNS server.
• also-notify-notifies the slave DNS server when there is any update on the zone files.

With these changes made, restart the DNS service on the Primary server.

sudo systemctl restart bind9

Step 2: Configure the Slave BIND DNS on Debian 11 | Debian 10

We will first install the bind9 package on Debian 11 | Debian 10 as below.

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

Then proceed and edit the slave server configuration file in /etc/bind/ directory. Install vim editor sudo apt install vim

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

In the file, add the following lines in the forward zone.

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

     type slave; //Secondary Slave DNS

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

     masters { 192.168.1.12; }; //Master Server IP

};

In the reverse zone:

zone "1.168.192.in-addr.arpa" IN { //Reverse lookup name. Should match your network in reverse order

     type slave; // Secondary/Slave DNS

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

     masters { 192.168.1.12; }; //Master Server IP

};

With the changes made, restart the server on ns2.computingforgeeks.local

sudo systemctl restart bind9

Step 3: Test the Slave DNS server on on Debian 11 | Debian 10

Now we test if the zone transfer was successful and the DNS server is working correctly. We need to set the client machine to use the slave as its DNS server.

$ sudo vim /etc/resolv.conf
nameserver 192.168.1.10

Now use the dig command to verify if the DNS is working.

dig www.computingforgeeks.local

Sample Output:

; <<>> DiG 9.16.1-Ubuntu <<>> www.computingforgeeks.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: 9873
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 1, ADDITIONAL: 2

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
; COOKIE: cca3340ee2f80f2b111d4e316120c5877d9c4c467fc68ef0 (good)
;; QUESTION SECTION:
;www.computingforgeeks.local.	IN	A

;; ANSWER SECTION:
www.computingforgeeks.local. 604800 IN	A	192.168.1.13

;; AUTHORITY SECTION:
computingforgeeks.local. 604800	IN	NS	ns1.computingforgeeks.local.

;; ADDITIONAL SECTION:
ns1.computingforgeeks.local. 604800 IN	A	192.168.1.12

;; Query time: 0 msec
;; SERVER: 192.168.1.10#53(192.168.1.10)
;; WHEN: Sat Aug 21 12:21:11 EAT 2021
;; MSG SIZE  rcvd: 134

You can use the below syntax to direct the query to the specific slave DNS and the output should be similar to the one above.

dig www.computingforgeeks.local @192.168.1.10

Sample Output.

From the output, it shows that the Master-slave setup is working correctly.

Conclusion

That is it! We have suce=cessfully configured a Slave BIND DNS Server on Debian 11 | Debian 10. I hope this was of significance.

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