How to Enable eBPF in the Kernel on OpenWrt

Extended Berkeley Packet Filter (eBPF) is a powerful tool for network monitoring, security, and performance enhancements. While OpenWrt does not enable eBPF by default, it can be configured manually. Follow this guide to enable eBPF in the kernel on OpenWrt.

1. Prerequisites

✔ A device running OpenWrt with a custom build setup. ✔ Basic knowledge of Linux kernel compilation. ✔ Enough storage and memory to support eBPF features. ✔ SSH access to the router and root privileges.

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2. Check If eBPF Is Already Enabled

Run the following command to check eBPF support:

uname -r
grep CONFIG_BPF /proc/config.gz

If you see CONFIG_BPF=n or no output, eBPF is not enabled, and you’ll need to compile OpenWrt with eBPF support.

3. Compiling OpenWrt with eBPF Support

Step 1: Clone OpenWrt Source Code

git clone https://git.openwrt.org/openwrt/openwrt.git
cd openwrt

Step 2: Configure Kernel Options

Run the configuration tool:

make menuconfig

Navigate to: ✔ Kernel Modules → Networking Support → Enable BPF (CONFIG_BPF=y) ✔ Kernel Modules → Enable eBPF JIT (CONFIG_BPF_JIT=y) ✔ Enable cBPF (CONFIG_CGROUP_BPF=y) for advanced filtering.

Save and exit.

Step 3: Compile OpenWrt with the New Kernel Config

make -j$(nproc)

This step will take time. Ensure your device has enough processing power and disk space.

4. Installing the Custom Build on OpenWrt

Once compiled, flash the new firmware:

sysupgrade -v /path/to/custom_openwrt.bin

Reboot the device:

reboot

After rebooting, confirm eBPF is enabled:

uname -r
grep CONFIG_BPF /proc/config.gz

5. Testing eBPF Functionality

You can test eBPF support using:

bpftool feature

For network monitoring, try:

tc filter add dev eth0 ingress bpf da obj example.o sec filter

Ensure that bpftool and iproute2 are installed for testing.

6. Final Thoughts

Enabling eBPF on OpenWrt provides advanced networking features, but requires kernel recompilation. Once enabled, you can utilize eBPF for monitoring, security, and performance optimizations.

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Frequently Asked Questions (FAQs)

Can I enable eBPF without recompiling OpenWrt?

✔ No, OpenWrt’s default kernel does not include eBPF support.

Does eBPF affect router performance?

✔ eBPF is efficient, but running complex programs may increase CPU usage.

What OpenWrt devices support eBPF?

✔ Devices with at least 256MB RAM and ARM/MIPS-based CPUs handle eBPF better.

By following this guide, you can enable eBPF in OpenWrt’s kernel and take advantage of advanced networking capabilities!