Install 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
Simply install the Hardware Enablement Stack (HWE), which provides newer kernel for Ubuntu LTS releases
sudo apt install --install-recommends linux-generic-hwe-16.04
sudo nano /etc/sysctl.conf
net.core.default_qdisc=fq net.ipv4.tcp_congestion_control=bbr
sudo sysctl -p
References
https://www.linuxbabe.com/ubuntu/enable-google-tcp-bbr-ubuntu