Ubuntu - Bind - Configure Bind9 - Caching Nameserver

The default configuration acts as a caching server.

Simply uncomment and edit /etc/bind/named.conf.options to set the IP addresses of the DNS servers you want to use; such as your ISP’s DNS servers:

forwarders {
    1.2.3.4;
    5.6.7.8;
};

NOTE: Replace 1.2.3.4 and 5.6.7.8 with the IP Addresses of actual nameservers.

To enable the new configuration, restart the DNS server:

sudo systemctl restart bind9.service

See dig for information on testing a caching DNS server.