May 28, 2023

Most DDoS attacks try to take advantage of any weak point they can find. DNS which stands for domain name service resolves all the ip addresses into domain names like


We need to make your DNS on your Ubuntu server as fast as possible so it can handle all types of attack packets without getting clogged.


Standard Ubuntu for some reason does not have this enabled so this is how you do it.


This tutorial shows you how to enable TCP BBR on Ubuntu. TCP BBR is a TCP congestion control algorithm developed by Google. It tackles the shortcomings of traditional TCP congestion control algorithms (Reno or CUBIC). According to Google, it can achieve orders of magnitude higher bandwidth and lower latency. TCP BBR is already being used on and YouTube servers, and the Internet Engineering Task Force (IETF) has been standardizing this algorithm Since July, 2017. BBR stands for Bottleneck Bandwidth and RTT.

BBR requires only changes on the sender side. You can enable TCP BBR on your Linux desktop to improve the overall web surfing experience. If you have a Linux web server, TCP BBR can achieve faster web page downloads for your website visitors.

Step 1: Check TCP Congestion Control Algorithms on Linux

By default, Linux uses the Reno and CUBIC congestion control algorithm. To check available congestion control algorithms, run the following command.

sysctl net.ipv4.tcp_available_congestion_control


net.ipv4.tcp_available_congestion_control = cubic reno

To check the current congestion control algorithm in use, run

sysctl net.ipv4.tcp_congestion_control


net.ipv4.tcp_congestion_control = cubic

Step 2: Make Sure You Have Linux Kernel 4.9 or Above

TCP BBR is supported by Linux since kernel version 4.9. Use the following command to check your Linux kernel version.

uname -r

Ubuntu 18.04 has kernel 4.13.


Ubuntu 20.04 uses kernel 5.4.


Ubuntu 22.04 uses kernel 5.15.


Step 3: Enable TCP BBR in Ubuntu

Once you have kernel 4.9 or above, edit sysctl.conf file.

sudo nano /etc/sysctl.conf

Add the following two lines at the end of the file.

ubuntu tcp bbr

Save and close the file. Then reload sysctl configurations.

sudo sysctl -p

If you have correctly added the above two lines in the file, then they will be included in the output like below.

linuxbabe@ubuntu:~$ sudo sysctl -p
net.core.default_qdisc = fq
net.ipv4.tcp_congestion_control = bbr

Now check the congestion control algorithm in use.

sysctl net.ipv4.tcp_congestion_control


net.ipv4.tcp_congestion_control = bbr

Congrats! You have successfully enabled TCP BBR on Ubuntu.

Speed Improvements

I used Shadowsocks proxy on a low-end VPS to test TCP BBR. The speed improvement is huge. The following screenshot shows YouTube connection speed before enabling TCP BBR on my proxy server. As you can see, the speed is only around 400Kb/s (50KB/s).

enable TCP BBR on Ubuntu 16.04

This is YouTube connection speed after enabling TCP BBR on my proxy server. 9878 Kb/s is about 1234 KB/s. My proxy server just got 24 times faster!

enable google tcp bbr ubuntu

On a second Shadowsocks proxy server, the speed went from around 10Mbit/s to around 62Mbit/s (64172Kbit/s) after enabling TCP BBR.

TCP BBR performance boost

Don’t disable TCP Window Scaling

You might need to disable TCP window scaling in order to fix a problem, but doing so can greatly reduce the network performance. Add the following line in /etc/sysctl.conf file to enable TCP window scaling.

net.ipv4.tcp_window_scaling = 1

Then apply the changes.

sudo sysctl -p

That’s it! I hope this tutorial helped you enable TCP BBR on Ubuntu.

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