vi /etc/sysctl.d/
disable-ipv6.conf
net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
Then issue sysctl -p
However you still try to contact IPv6 addresses, so the solution consists in adding this line
ip_resolve=4
to
/etc/yum.conf