How to Enable Google BBR on CentOS 7

---

BBR (Bottleneck Bandwidth and Round-trip propagation time) is a new congestion control algorithm developed at Google. Congestion control algorithms running inside every computer, phone, or tablet connected to a network that decides how fast to send data.

Install a newer Kernel

---

Since CentOS 7 ships with the 3.10.x kernel, which does not include BBR by default, we need to upgrade to a newer kernel version on your machine to use BBR.

For this, we install the ELRepo repo,

rpm --import https://www.elrepo.org/RPM-GPG-KEY-elrepo.org

rpm -Uvh http://www.elrepo.org/elrepo-release-7.0-2.el7.elrepo.noarch.rpm

Output:

[root@vps ~]# rpm --import https://www.elrepo.org/RPM-GPG-KEY-elrepo.org
[root@vps ~]# rpm -Uvh http://www.elrepo.org/elrepo-release-7.0-2.el7.elrepo.noarch.rpm
Retrieving http://www.elrepo.org/elrepo-release-7.0-2.el7.elrepo.noarch.rpm
Retrieving http://elrepo.org/elrepo-release-7.0-4.el7.elrepo.noarch.rpm
Preparing...                          ################################# [100%]
Updating / installing...
   1:elrepo-release-7.0-4.el7.elrepo  ################################# [100%]
[root@vps ~]#

To install kernel using the ELRepo repo,

yum --enablerepo=elrepo-kernel install kernel-ml -y

Output:

Dependencies Resolved

================================================================================
 Package        Arch        Version                    Repository          Size
================================================================================
Installing:
 kernel-ml      x86_64      5.12.9-1.el7.elrepo        elrepo-kernel       53 M

Transaction Summary
================================================================================
Install  1 Package
.
.
.
Installed:
  kernel-ml.x86_64 0:5.12.9-1.el7.elrepo

Complete!

Now check the stable kernel installation by using the following command,

rpm -qa | grep kernel

Note: If the installation is successful, you should see kernel-ml-5.xx.xx.elrepo.x86_64 among the output list:

Output:

[root@vps ~]# rpm -qa | grep kernel
kernel-3.10.0-1160.el7.x86_64
kernel-tools-3.10.0-1160.el7.x86_64
kernel-ml-5.12.9-1.el7.elrepo.x86_64
kernel-tools-libs-3.10.0-1160.el7.x86_64
[root@vps ~]#

Boot into the newer Kernel

---

Next, you need to boot into the latest kernel by setting it as the default grub2 boot entry.

Command to show all entries in the grub2 menu,

egrep ^menuentry /etc/grub2.cfg | cut -f 2 -d \'

Output:

[root@vps ~]# egrep ^menuentry /etc/grub2.cfg | cut -f 2 -d \'
CentOS Linux 7 Rescue 13f95ded0c4147935ac6afed832cfb0a (5.12.9-1.el7.elrepo.x86_64)
CentOS Linux (5.12.9-1.el7.elrepo.x86_64) 7 (Core)
CentOS Linux (3.10.0-1160.el7.x86_64) 7 (Core)
CentOS Linux (0-rescue-dd1973a114f84ea8bbf37b494513d3f7) 7 (Core)

Use the following command to set the default boot entry,

Note: The count starts from 0 and the latest stable kernel is on the second line thus we set it to 1

For example,

[root@vps ~]# egrep ^menuentry /etc/grub2.cfg | cut -f 2 -d \'
CentOS Linux 7 Rescue 13f95ded0c4147935ac6afed832cfb0a (5.12.9-1.el7.elrepo.x86_64)  <-- 0
CentOS Linux (5.12.9-1.el7.elrepo.x86_64) 7 (Core)                                   <-- 1
CentOS Linux (3.10.0-1160.el7.x86_64) 7 (Core)                                       <-- 2
CentOS Linux (0-rescue-dd1973a114f84ea8bbf37b494513d3f7) 7 (Core)                    <-- 3

grub2-set-default 1

Reboot the server

shutdown -r now

Once the server is back online, confirm that you are using the correct kerne.

uname -r

Output:

[root@vps ~]# uname -r
5.12.9-1.el7.elrepo.x86_64

Enable Google BBR.

---

You need to modify systctl as follows to enable the Google BBR algorithm.

echo 'net.core.default_qdisc=fq' | tee -a /etc/sysctl.conf

echo 'net.ipv4.tcp_congestion_control=bbr' | tee -a /etc/sysctl.conf

sysctl -p

Output:

[root@vps ~]# echo 'net.core.default_qdisc=fq' | tee -a /etc/sysctl.conf
net.core.default_qdisc=fq
[root@vps ~]# echo 'net.ipv4.tcp_congestion_control=bbr' | tee -a /etc/sysctl.conf
net.ipv4.tcp_congestion_control=bbr
[root@vps ~]# sysctl -p
net.core.default_qdisc = fq
net.ipv4.tcp_congestion_control = bbr

Run the following command to verify if BBR is enabled,

sysctl net.ipv4.tcp_available_congestion_control

Output:

[root@vps ~]# sysctl net.ipv4.tcp_available_congestion_control
net.ipv4.tcp_available_congestion_control = reno cubic bbr

Finally, execute the following command to verify the Google BBR,

lsmod | grep bbr

Output:

[root@vps ~]# lsmod | grep bbr
tcp_bbr                20480  1

Congratulations! You have successfully installed TCP BBR Congestion Control.