Using eBPF for Traffic Redirection in Istio Ambient Mode

Why Use eBPF

While implementing traffic redirection in Istio ambient mode, performance is important, but programmability is equally critical to support diverse and customizable forwarding rules. eBPF leverages additional kernel context to bypass complex routing and quickly direct packets to their final destination, offering deeper packet visibility and flexible flow management compared to iptables.

How eBPF Traffic Redirection Works

An eBPF program is pre‑compiled into the Istio CNI component and attached to the traffic control ingress and egress hook points. The istio-cni component watches Pod events and loads or unloads the eBPF program on the network interface of Pods that join or leave the ambient mesh.

Replacing iptables with eBPF eliminates the need for Geneve encapsulation and allows traffic forwarding to be customized entirely in kernel space, improving both performance and flexibility.

Using eBPF in Ambient Mode

First, set up your cluster according to the Istio Ambient Mesh guide, then modify the installation command to enable eBPF redirection:

istioctl install --set profile=ambient --set values.cni.ambient.redirectMode="ebpf"

Verify that eBPF redirection is active by checking the istio-cni logs:

ambient Writing ambient config: {"ztunnelReady":true,"redirectMode":"eBPF"}

Performance Improvements

Latency and throughput (QPS) with eBPF redirection are slightly better than with iptables. Tests were run in a kind cluster where a Fortio client and server operated on the same node under ambient mode (eBPF debug logs disabled). Example load command:

fortio load -uniform -t 60s -qps 0 -c
http://
:8080

Higher QPS tests (e.g., 8000 QPS) also showed improved P75 latency with eBPF compared to iptables.

Conclusion

Both eBPF and iptables have strengths and weaknesses for traffic redirection. eBPF provides a modern, flexible, and high‑performance alternative with richer rule customization, but requires a recent Linux kernel (≥ 4.20). iptables remains widely compatible with older kernels but lacks eBPF's flexibility and may deliver lower performance. The choice depends on system requirements, kernel version, and user expertise. Contributions to integrate eBPF with various CNI plugins are welcome; join the discussion on the Istio Slack #ambient channel.