vps.taxi

Enable BBR

BBR is a TCP congestion control algorithm built into the Linux kernel. On the systems we offer, two settings turn it on; no new kernel and no third-party script are needed.

1. Check what is in use now

Log in as root (see Log in with SSH) and run:

sysctl net.ipv4.tcp_congestion_control
sysctl net.ipv4.tcp_available_congestion_control

If the first line already says bbr, BBR is on and there is nothing to do.

2. Turn on BBR

cat > /etc/sysctl.d/99-bbr.conf <<'EOF'
net.core.default_qdisc = fq
net.ipv4.tcp_congestion_control = bbr
EOF
sysctl --system

This works on every system we offer (Ubuntu 26.04, Ubuntu 24.04, Ubuntu 22.04, Debian 13, Debian 12, AlmaLinux 9, Rocky Linux 9): their kernels include BBR. No reboot is needed, and the setting stays after reboots.

3. Check that it works

sysctl net.ipv4.tcp_congestion_control
sysctl net.core.default_qdisc

You should see bbr and fq. Connections opened from now on use BBR; restart long-running programs (for example a proxy server) so that their connections use it too.

4. What BBR changes

  • BBR controls how your server sends TCP data, so it affects downloads from your server. UDP traffic is not affected.
  • The port speed of your plan is the cap for the whole server, in both directions. A single TCP connection often stays below it; several connections together get closer to it. For a speed test, try different speed-test servers and a multi-connection download tool, for example aria2c -x 8 -s 8 URL.

Avoid “one-click” scripts that replace the kernel or the system image. When you change the IP address in the client area, the new address is written into the system through cloud-init; with a custom kernel or a replaced image it may not be written in.

5. Turn BBR off again

rm /etc/sysctl.d/99-bbr.conf
reboot

After the reboot the system defaults apply again. A reinstall also starts with the defaults, so run step 2 again after reinstalling.