eBPF (extended Berkeley Packet Filter) is a Linux kernel technology that allows small, secure programs to run directly inside the kernel without modifying kernel source code.

In Cilium, eBPF is mainly used for:

• High-performance networking between Kubernetes pods and nodes
• Network policy & security enforcement
• Service load balancing and routing
• Traffic monitoring & observability with Hubble
• Reducing or replacing traditional iptables-based packet processing

In short: eBPF gives Cilium a programmable, efficient way to control and observe network traffic directly inside the Linux kernel.

In simple terms:

Pod → eBPF (Cilium) → Network → eBPF → Pod

eBPF allows Cilium to provide things such as network policies, load balancing, routing, service handling, and network visibility, often without relying heavily on traditional iptables.