How To Enable TCP BBR on AlmaLinux 9

In this guide, we want to teach you How To Enable TCP BBR on AlmaLinux 9.

Introduction to TCP BBR

The internet is built based on a basic approach that assumes the network consists of a bunch of nodes and edges or links. When a packet traverses the network, it passes from one node to another. The recipient node is responsible for selecting the next node to forward the packet and move closer to the required destination. If the selected path to the destination is busy, the packet will stay in a queue and wait to be processed later. If the queue is full, then the packet is dropped. This is called network congestion, which occurs when a network node or link is carrying more data than it can handle.

Today’s internet is distributed across billions of devices, which establish billions of connections at a time ranging from wired connections to wireless. This increases the possibility of network congestion. As a result, a congestion control algorithm is a necessity to solve such matters. This is why TCP BBR was developed.

TCP BBR is a TCP congestion control algorithm built for the congestion of the modern internet. It stands for Transmission Control Protocol Bottleneck Bandwidth and Round-trip propagation time (TCP BBR), and it was developed by Google in 2016.

Steps To To Enable TCP BBR on AlmaLinux 9

To complete this guide, you must log in to your server as a non-root user with sudo privileges. To do this, you can follow our guide the Initial Server Setup with AlmaLinux 9.

Enable BBR on AlmaLinux 9

First, you need to update and upgrade your local package index with the following command:

sudo dnf update && sudo dnf upgrade -y

Then, you need to check your existing congestion controls on your server.

Check Existing Congestion Control Algorithms

Typically, Linux uses reno and cubic algorithms.

At this point, you need to run the following command to check what existing TCP congestion controls are in place:

sudo sysctl net.ipv4.tcp_congestion_control

Output
net.ipv4.tcp_congestion_control = cubic

In the above output, cubic is employed in our system, but your output may show different results.

Next, list available TCP congestion control algorithms on your server by using the following command:

sudo sysctl net.ipv4.tcp_available_congestion_control

Output
net.ipv4.tcp_available_congestion_control = reno cubic

From the output, reno and cubic are available, and once BBR has been added/enabled, this should feature BBR.

Add TCP BBR on AlmaLinux 9

Now that you have checked the basics to confirm the available algorithms, you need to open the sysctl.conf file. Here we use the vi editor to open the file:

sudo vi /etc/sysctl.conf

Add the following content to the file:

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

When you are done, save and close the file.

Then, reload the configuration file with the command below:

sudo sysctl -p

Output
net.core.default_qdisc = fq
net.ipv4.tcp_congestion_control = bbr

At this point, you need to verify that  BBR is enabled and active as the new TCP congestion control by using the following command on AlmaLinux 9:

sudo sysctl net.ipv4.tcp_congestion_control

Output
net.ipv4.tcp_congestion_control = bbr

Also, you can use the command below to verify it:

lsmod | grep bbr

Output
tcp_bbr                20480  1

Finally, list available TCP congestion controls on your server again:

sudo sysctl net.ipv4.tcp_available_congestion_control

You should see BBR in your list:

Output
net.ipv4.tcp_available_congestion_control = reno cubic bbr

That’s it. You have successfully added BBR to your server.

Conclusion

At this point, you have learned to Enable BBR on AlmaLinux 9.

Hope you enjoy it.

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