Requirements for Linux server Internet speed with TCP BBR

Make sure that your Linux kernel has the following option compiled as either module or inbuilt into the Linux kernel:

1. CONFIG_TCP_CONG_BBR
2. CONFIG_NET_SCH_FQ

Linux TCP BBR congestion control

You must use the Linux kernel version 4.9 or above. On a Debian/Ubuntu Linux type the following grep command/egrep command:
$ grep 'CONFIG_TCP_CONG_BBR' /boot/config-$(uname -r)
$ grep 'CONFIG_NET_SCH_FQ' /boot/config-$(uname -r)
$ egrep 'CONFIG_TCP_CONG_BBR|CONFIG_NET_SCH_FQ' /boot/config-$(uname -r)
Sample outputs:

Fig.01: Make sure that your Linux kernel has TCP BBR option setup

I am using Linux kernel version 4.9.0-8-amd64 on a Debian and 4.18.0-15-generic on an Ubuntu server. If above options not found, you need to either compile latest kernel or install the latest version of Linux kernel using the apt-get command/apt command.

Run test before you enable TCP BBR to improve network speed

Type the following command on Linux server:
# iperf -s

Execute the following on your Linux client:
$ iperf -c gcvm.backup -i 2 -t 30

How to enable TCP BBR congestion control on Linux

Edit the /etc/sysctl.conf file or create a new file in /etc/sysctl.d/ directory:
$ sudo vi /etc/sysctl.conf
OR
$ sudo vi /etc/sysctl.d/10-custom-kernel-bbr.conf
Append the following two lines:
net.core.default_qdisc=fq
net.ipv4.tcp_congestion_control=bbr
Save and close the file i.e. exit from the vim/vi text editor by typing :x!. Next you must either reboot the Linux box or reload the changes using the sysctl command:
$ sudo reboot
OR
$ sudo sysctl --system
Sample outputs:

* Applying /etc/sysctl.d/10-console-messages.conf ...
kernel.printk = 4 4 1 7
* Applying /etc/sysctl.d/10-custom.conf ...
net.core.default_qdisc = fq
net.ipv4.tcp_congestion_control = bbr
* Applying /etc/sysctl.d/10-ipv6-privacy.conf ...
net.ipv6.conf.all.use_tempaddr = 2
net.ipv6.conf.default.use_tempaddr = 2
* Applying /etc/sysctl.d/10-kernel-hardening.conf ...
kernel.kptr_restrict = 1
* Applying /etc/sysctl.d/10-link-restrictions.conf ...
fs.protected_hardlinks = 1
fs.protected_symlinks = 1
* Applying /etc/sysctl.d/10-lxd-inotify.conf ...
fs.inotify.max_user_instances = 1024
* Applying /etc/sysctl.d/10-magic-sysrq.conf ...
kernel.sysrq = 176
* Applying /etc/sysctl.d/10-network-security.conf ...
net.ipv4.conf.default.rp_filter = 1
net.ipv4.conf.all.rp_filter = 1
net.ipv4.tcp_syncookies = 1
* Applying /etc/sysctl.d/10-ptrace.conf ...
kernel.yama.ptrace_scope = 1
* Applying /etc/sysctl.d/10-zeropage.conf ...
vm.mmap_min_addr = 65536
* Applying /etc/sysctl.d/99-sysctl.conf ...
* Applying /etc/sysctl.conf ...

You can verify new settings with the following sysctl command. Run:
$ sysctl net.core.default_qdisc
net.core.default_qdisc = fq
$ sysctl net.ipv4.tcp_congestion_control
net.ipv4.tcp_congestion_control = bbr

Test BBR congestion control on Linux

In my testing between two long distance Linux server with Gigabit ports connected to the Internet, I was able to bump 250 Mbit/s into 800 Mbit/s. You can use tools such as the wget command to measure bandwidths speed:
$ wget https://your-server-ip/file.iso
I also noticed I was able to push almost 100 Mbit/s for my OpenVPN traffic. Previously I was able to push up to 30-40 Mbit/s only. Overall I am quite satisfied with TCP BBR congestion control option for my Linux box.

Linux TCP BBR test with iperf

The iperf is a commonly used network testing tool for TCP/UDP data streams. It measures the throughput of the network. This tool can validate the importance of Linux TCP BBR settings.

Type command on Linux server with TCP BBR congestion control enables

# iperf -s
Sample outputs:

------------------------------------------------------------
Server listening on TCP port 5001
TCP window size: 85.3 KByte (default)
------------------------------------------------------------
[  4] local 10.128.0.2 port 5001 connected with AAA.BB.C.DDD port 46978
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-30.6 sec   127 MBytes  34.7 Mbits/sec

Type command on Linux/Unix client

$ iperf -c YOUR-Linux-Server-IP-HERE -i 2 -t 30
Sample output when connected to TCP BBR congestion enabled on Linux:

------------------------------------------------------------
Client connecting to gcp-vm-nginx-www1, TCP port 5001
TCP window size: 45.0 KByte (default)
------------------------------------------------------------
[  3] local 10.8.0.2 port 46978 connected with xx.yyy.zzz.tt port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0- 2.0 sec  4.00 MBytes  16.8 Mbits/sec
[  3]  2.0- 4.0 sec  8.50 MBytes  35.7 Mbits/sec
[  3]  4.0- 6.0 sec  10.9 MBytes  45.6 Mbits/sec
[  3]  6.0- 8.0 sec  16.2 MBytes  68.2 Mbits/sec
[  3]  8.0-10.0 sec  5.29 MBytes  22.2 Mbits/sec
[  3] 10.0-12.0 sec  9.38 MBytes  39.3 Mbits/sec
[  3] 12.0-14.0 sec  8.12 MBytes  34.1 Mbits/sec
[  3] 14.0-16.0 sec  8.12 MBytes  34.1 Mbits/sec
[  3] 16.0-18.0 sec  8.38 MBytes  35.1 Mbits/sec
[  3] 18.0-20.0 sec  6.75 MBytes  28.3 Mbits/sec
[  3] 20.0-22.0 sec  8.12 MBytes  34.1 Mbits/sec
[  3] 22.0-24.0 sec  8.12 MBytes  34.1 Mbits/sec
[  3] 24.0-26.0 sec  9.50 MBytes  39.8 Mbits/sec
[  3] 26.0-28.0 sec  7.00 MBytes  29.4 Mbits/sec
[  3] 28.0-30.0 sec  8.12 MBytes  34.1 Mbits/sec
[  3]  0.0-30.3 sec   127 MBytes  35.0 Mbits/sec

Conclusion

Bottleneck Bandwidth and RTT (BBR) congestion control pre and post average stats collected for 30 seconds using the iperf command:

1. PRE BBR: Transfer: 27.5 MBytes. Bandwidth: 7.15 Mbits/sec
2. POST BBR: Transfer: 127 MBytes. Bandwidth: 35.0 Mbits/sec

BBR is, in my opinion, one of the most critical improvements to Linux networking stacks in recent years. This page demonstrated how to enable and set up BBR on Linux based system. For more information see the following pages:

• Measure Network Performance: Find Bandwidth, Jitter, Datagram Loss With Iperf
• BBR info from Google
• TCP BBR congestion control comes to GCP. Your Internet just got faster

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By Kevin Young

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