sed -i -e 's/alias net-pf-10 ipv6/#&\nalias net-pf-10 off/' /etc/modprobe.d/aliases

/etc/modprobe.d/blacklist.local

blacklist nf_nat_h323
blacklist nf_conntrack_h323
blacklist ipv6

https://help.ubuntu.com/community/WebBrowsingSlowIPv6IPv4