====== BBR ======
BBR is the optimization for the tcp, and it can increase the network speed significant. So it's the same as [[linux:kcptun|kcptun]].

===== BBR on Raspberry Pi =====
Check the kernel version, the kernel is already 4.9+, so it already support bbr
<code>
pi@raspberrypi:~ $ uname -a
Linux raspberrypi 4.9.35-v7+ #1014 SMP Fri Jun 30 14:47:43 BST 2017 armv7l GNU/Linux
</code>

==== Enable bbr ====
  sysctl net.core.default_qdisc=fq
  sysctl net.ipv4.tcp_congestion_control=bbr

<code BASH>
pi@raspberrypi:~ $  sudo sysctl net.ipv4.tcp_congestion_control=bbr
net.ipv4.tcp_congestion_control = bbr
pi@raspberrypi:~ $  lsmod |grep bbr
tcp_bbr                 6366  18
pi@raspberrypi:~ $  sysctl net.ipv4.tcp_available_congestion_control
net.ipv4.tcp_available_congestion_control = bbr cubic reno
pi@raspberrypi:~ $  sysctl net.ipv4.tcp_congestion_control
net.ipv4.tcp_congestion_control = bbr
</code>

==== DigitalOcean enable BBR ====
Refer
  - https://www.digitalocean.com/community/tutorials/how-to-update-a-digitalocean-server-s-kernel
Install the grub loader in the console panel, first you need power off, then after install the grub loader, then power on.

Install the new kernel, you can find the kernel what you want 
  apt-cache search --names-only linux-image

   sudo apt-get install linux-image-4.11.0-13-generic linux-headers-4.11.0-13-generic
Or
  sudo apt-get install linux-image-4.10.0-42-generic linux-headers-4.10.0-42-generic
 
Actuall after install the above kernel, it doesn't support BBR, and the working kernel is following one, you need manual download and install it

  cd kernel4.9/
  wget http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.9/linux-image-4.9.0-040900-generic_4.9.0-040900.201612111631_amd64.deb
  sudo dpkg -i linux-image-4.9.0-040900-generic_4.9.0-040900.201612111631_amd64.deb

Update the grub
  sudo vim /etc/default/grub
Add the line:  
  GRUB_DISABLE_SUBMENU = Y
  
  export GRUB_CONFIG=`sudo find /boot -name "grub.cfg"`
  sudo update-grub

Now you find all the kernel
  grep 'menuentry ' $GRUB_CONFIG | cut -f 2 -d "'" | nl -v 0
And you need update /etc/default/grub, and set update the index to the one your want
  GRUB_DEFAULT=0
Now you can reoot the VPS
  

==== Some tips ====
<code>
uname -r
＃查看内核版本，含有4.9.0就表示OK了
＃------------
sysctl net.ipv4.tcp_available_congestion_control
＃返回值一般为：
＃net.ipv4.tcp_available_congestion_control = bbr cubic reno
＃------------
sysctl net.ipv4.tcp_congestion_control
＃返回值一般为：
＃net.ipv4.tcp_congestion_control = bbr
＃------------
sysctl net.core.default_qdisc
＃返回值一般为：
＃net.core.default_qdisc = fq
＃------------
lsmod | grep bbr
＃返回值有tcp_bbr模块即说明bbr已启动。
</code>

==== Refer ====
  - https://www.nmbhost.com/archives/1594
  - https://blog.chenjia.me/articles/161229-000832.html
  - https://www.digitalocean.com/community/tutorials/how-to-update-a-digitalocean-server-s-kernel