安装4.9内核
rpm --import https://www.elrepo.org/RPM-GPG-KEY-elrepo.org
rpm -Uvh http://www.elrepo.org/elrepo-release-6-6.el6.elrepo.noarch.rpm
yum --enablerepo=elrepo-kernel install kernel-ml -y
vi /etc/grub.conf 改 default=0

重启
uname -r看内核是不是4.9

执行
echo "net.core.default_qdisc=fq" >> /etc/sysctl.conf
echo "net.ipv4.tcp_congestion_control=bbr" >> /etc/sysctl.conf

sysctl -p