In this article, I will show you how to deploy BBR on a Vultr CentOS 7 KVM server instance.

Prerequisites

• A Vultr CentOS 7 x64 server instance.
• A sudo user.

Step 1: Upgrade the kernel using the ELRepo RPM repository

In order to use BBR, you need to upgrade the kernel of your CentOS 7 machine to 4.9.0. You can easily get that done using the ELRepo RPM repository.

Before the upgrade, you can take a look at the current kernel:

uname -r

This command should output a string which resembles:

3.10.0-514.2.2.el7.x86_64

As you see, the current kernel is 3.10.0.

Install the ELRepo repo:

sudo rpm --import https://www.elrepo.org/RPM-GPG-KEY-elrepo.org && sudo rpm -Uvh http://www.elrepo.org/elrepo-release-7.0-2.el7.elrepo.noarch.rpm

Install the 4.9.0 kernel using the ELRepo repo:

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

Confirm the result:

rpm -qa | grep kernel

If the installation is successful, you should see kernel-ml-4.9.0-1.el7.elrepo.x86_64 among the output list:

kernel-ml-4.9.0-1.el7.elrepo.x86_64
kernel-3.10.0-514.el7.x86_64
kernel-tools-libs-3.10.0-514.2.2.el7.x86_64
kernel-tools-3.10.0-514.2.2.el7.x86_64
kernel-3.10.0-514.2.2.el7.x86_64

Now, you need to enable the 4.9.0 kernel by setting up the default grub2 boot entry.

Show all entries in the grub2 menu:

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

The result should resemble:

CentOS Linux 7 Rescue a0cbf86a6ef1416a8812657bb4f2b860 (4.9.0-1.el7.elrepo.x86_64)
CentOS Linux (4.9.0-1.el7.elrepo.x86_64) 7 (Core)
CentOS Linux (3.10.0-514.2.2.el7.x86_64) 7 (Core)
CentOS Linux (3.10.0-514.el7.x86_64) 7 (Core)
CentOS Linux (0-rescue-bf94f46c6bd04792a6a42c91bae645f7) 7 (Core)

Since the line count starts at 0 and the 4.9.0 kernel entry is on the second line, set the default boot entry as 1:

sudo grub2-set-default 1

Reboot the system:

sudo shutdown -r now

When the server is back online, log back in and rerun the uname command to confirm that you are using the correct Kernel:

uname -r

You should see the result as below:

4.9.0-1.el7.elrepo.x86_64

Step 2: Enable BBR

In order to enable the BBR algorithm, you need to modify the sysctl configuration as follows:

echo 'net.core.default_qdisc=fq' | sudo tee -a /etc/sysctl.conf
echo 'net.ipv4.tcp_congestion_control=bbr' | sudo tee -a /etc/sysctl.conf
sudo sysctl -p 

Now, you can use the following commands to confirm that BBR is enabled:

sudo sysctl net.ipv4.tcp_available_congestion_control

The output should resemble:

net.ipv4.tcp_available_congestion_control = bbr cubic reno 

Next, verify with:

sudo sysctl -n net.ipv4.tcp_congestion_control

The output should be:

bbr

Finally, check that the kernel module was loaded:

lsmod | grep bbr

The output will be similar to:

tcp_bbr                16384  0

Step 3 (optional): Test the network performance enhancement

In order to test BBR's network performance enhancement, you can create a file in the web server directory for download, and then test the download speed from a web browser on your desktop machine.

sudo yum install httpd -y
sudo systemctl start httpd.service
sudo firewall-cmd --zone=public --permanent --add-service=http
sudo firewall-cmd --reload
cd /var/www/html
sudo dd if=/dev/zero of=500mb.zip bs=1024k count=500 

Finally, visit the URL http://[your-server-IP]/500mb.zip from a web browser on your desktop computer, and then evaluate download speed.

That's all. Thank you for reading.