If IPv6 is not used in your network, you can disable IPv6 easily.
$ sudo vi /etc/sysctl.confAdd these lines into the file
net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1Save and quit (<esc>:wq!)
$ sudo sysctl -p