How to Enable BBR on Debian 13 (Trixie)

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BBR (Bottleneck Bandwidth and Round-trip propagation time) is a modern TCP congestion control algorithm that can significantly improve network speed and latency.

Check Kernel Version

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BBR requires Linux kernel 4.9+, which Debian 13 already includes.

uname -r

Output:

root@server:~# uname -r
6.12.38+deb13-amd64

Make sure it shows >= 4.9.

Load BBR Module

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Run the following to load the tcp_bbr module:

modprobe tcp_bbr

Confirm it loaded:

lsmod | grep bbr

Output:

root@server:~# lsmod | grep bbr
tcp_bbr                20480  0

Enable BBR in sysctl

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Edit the sysctl configuration:

nano /etc/sysctl.d/99-bbr.conf

Add these lines into the file:

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

Apply the changes:

sysctl --system

Output:

root@server:~# sysctl --system
* Applying /usr/lib/sysctl.d/10-coredump-debian.conf ...
* Applying /usr/lib/sysctl.d/50-default.conf ...
* Applying /usr/lib/sysctl.d/50-pid-max.conf ...
* Applying /etc/sysctl.d/99-bbr.conf ...
kernel.core_pattern = core
kernel.sysrq = 0x01b6
kernel.core_uses_pid = 1
net.ipv4.conf.default.rp_filter = 2
net.ipv4.conf.ens3.rp_filter = 2
net.ipv4.conf.lo.rp_filter = 2
net.ipv4.conf.default.accept_source_route = 0
net.ipv4.conf.ens3.accept_source_route = 0
net.ipv4.conf.lo.accept_source_route = 0
net.ipv4.conf.default.promote_secondaries = 1
net.ipv4.conf.ens3.promote_secondaries = 1
net.ipv4.conf.lo.promote_secondaries = 1
net.ipv4.ping_group_range = 0 2147483647
net.core.default_qdisc = fq_codel
fs.protected_hardlinks = 1
fs.protected_symlinks = 1
fs.protected_regular = 2
fs.protected_fifos = 1
vm.max_map_count = 1048576
kernel.pid_max = 4194304
net.core.default_qdisc = fq
net.ipv4.tcp_congestion_control = bbr

Verify BBR Is Enabled

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Run:

sysctl net.ipv4.tcp_congestion_control

Output:

root@server:~# sysctl net.ipv4.tcp_congestion_control
net.ipv4.tcp_congestion_control = bbr

Also verify with:

sysctl net.core.default_qdisc

Ooutput:

root@server:~# sysctl net.core.default_qdisc
net.core.default_qdisc = fq

Confirm BBR is active:

lsmod | grep bbr

You should see:

tcp_bbr                20480  1

Conclusion

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BBR is now enabled and active on your Debian 13 system.

You should notice better network performance, especially for high-latency or high-bandwidth connections.

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Optional: Reboot to Confirm Persistence

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reboot

After rebooting, repeat the verification steps to ensure BBR remains active.