For most Ubuntu users, disabling IPv6 can increase the Internet speed on their system if they feel that it is slower than what it used to be on Windows or Mac.
Follow the instructions:
First check that your Internet connection makes use of IPv4 or not. Go to ip-lookup.netand click on Conversations. It will tell you if you are using IPv4 or not. If it is using IPv4, we can disable IPv6, otherwise this tutorial will not be applicable.
Now we need to add a line to sysctl.conf. Run the follwing command: sudo gedit /etc/sysctl.conf
At the end of the text file, add the following line: net.ipv6.conf.all.disable_ipv6 = 1
Restart your computer or reload sysctl.cong by running command: sudo sysctl -p. To check that it has been disabled or not, run following command in terminal: ip a | grep inet
If the terminal does not show any output then IPv6 has been disabled.