Fix slow internet connection ubuntu

I've found the cause of the issue. The slow connection was because of IPv6 configuration. When I disabled IPv6, everything worked fine.

$ sudo nano /etc/sysctl.conf

Added these configurations at the end of file:

# IPv6
net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1

Then restarted sysctl.conf:

$ sudo sysctl -p