I have tried a lot of tutorials but, could not find anything that works out of the box for Ubuntu 18.04 fresh install. What I have found is that ubuntu 18.04 comes pre-installed with dnsmasq-base which I had to remove to install the full dnsmasq.

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sudo apt-get remove dnsmasq-base
sudo apt-get install dnsmasq

Edit the dnsmasq config file

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sudo vim /etc/dnsmasq.conf

and add the below mentioned lines

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interface=lo
bind-interfaces
listen-address=127.0.0.1

Check if the network manager has dnsmasq line, if yes, then remove it

Restart NetworkManager

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sudo /etc/init.d/network-manager restart

Retsart dnsmasq

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sudo /etc/init.d/dnsmasq restart

And you should be good to go.