Enable BBR to speed up TCP

Debian 9 or Ubuntu 17.04 contains kernel above 4.9, and not needed to update.

For Debian 8, you can install version 4.9 by the following commands:

apt-get install linux-base -t jessie-backports
apt-get install linux-image-4.9.0-0.bpo.6-amd64

For other Debian based Linux, download and install the latest kernel manually from the following url:
http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.18.3/

Config the kernel parameters

edit file /etc/sysctl.conf

net.ipv4.tcp_syncookies = 1
net.ipv4.tcp_tw_reuse = 1
net.ipv4.tcp_tw_recycle = 0
net.ipv4.tcp_fin_timeout = 30
net.ipv4.tcp_keepalive_time = 1200
net.ipv4.ip_local_port_range = 10000 65000
net.ipv4.tcp_max_syn_backlog = 8192
net.ipv4.tcp_max_tw_buckets = 5000
net.ipv4.tcp_fastopen = 3
net.ipv4.tcp_rmem = 4096 87380 67108864
net.ipv4.tcp_wmem = 4096 65536 67108864
net.ipv4.tcp_mtu_probing = 1
net.ipv4.tcp_congestion_control = bbr

fs.file-max = 51200

net.core.rmem_max = 67108864
net.core.wmem_max = 67108864
net.core.netdev_max_backlog = 250000
net.core.somaxconn = 4096
net.core.default_qdisc = fq

Make kernel parameters changes permanent
sudo sysctl -p