setup-ipsec-vpn/docs/bbr.md

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Advanced usage: Deploy Google BBR congestion control algorithm

Google BBR is a congestion control algorithm that could significantly increase server throughput and reduce latency.

Google BBR has been built into Linux kernel 4.9 and higher, but needs to be manually turned on.

To learn more about the Google BBR algorithm, see this official blog or this official repository.

Prepare

You can check the current Linux kernel version with the command uname -r. When the version is greater than or equal to 4.9, you can deploy BBR directly by referring to the instructions below.

Generally speaking, the kernel versions of Ubuntu 18.04+, Debian 10+, CentOS 8+ and RHEL 8+ are greater than 4.9. But for Amazon Linux 2, you need to update the kernel in the following ways before deploying Google BBR.

Amazon Linux 2

Amazon Linux 2 provides newer versions of the verified Linux kernel, which can be installed from the Extras repository.

1. Install kernel-ng from the Extras repository

   sudo amazon-linux-extras install kernel-ng
   

2. Update packages

   sudo yum update
   

3. Restart the system

   sudo reboot
   

4. Check the Linux kernel version

   uname -r
   

Deploy Google BBR

In this section, we will start Google BBR by modifying the configuration file.

1. Backup /etc/sysctl.conf

   sudo cp /etc/sysctl.conf /etc/sysctl.conf.backup
   

2. Modify /etc/sysctl.conf

   sudo vim /etc/sysctl.conf
   

   Add the following lines to the file

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

3. Enable Google BBR
   First, check your server's kernel version using uname -r.
   For kernel versions >= 4.20, apply sysctl settings:

   sudo sysctl -p
   

   For kernel versions < 4.20, you must reboot the server:

   sudo reboot
   

4. Check Google BBR status

   sudo sysctl net.ipv4.tcp_available_congestion_control
   # net.ipv4.tcp_available_congestion_control = reno cubic bbr
   sudo sysctl -n net.ipv4.tcp_congestion_control
   # bbr
   lsmod | grep bbr
   # tcp_bbr  16384  0
   

Document author

Copyright (C) 2022 Leo Liu
Translated by Lin Song