Technical explanation
D most precisely describes Cilium’s foundational use of eBPF. The Cilium agent translates desired networking and security state into eBPF programs and maps, then attaches those programs to Linux kernel hook points such as traffic-control ingress and egress, XDP, cgroups, and sockets. Packets can consequently be classified, permitted, dropped, redirected, load-balanced, or forwarded without requiring changes to the protected application.
Endpoint-policy programs associate traffic with Cilium security identities and perform Layer 3 and Layer 4 enforcement in the kernel. Traffic requiring Layer 7 inspection can be redirected from the eBPF datapath to Envoy. This combination provides efficient kernel-level enforcement while retaining application-aware controls.
Option A describes an important Hubble observability outcome, but it is narrower than Cilium’s primary networking and enforcement model and overstates what is necessarily exposed through a UI. Option B mischaracterizes Cilium as DNS infrastructure; Cilium can enforce DNS-aware policies but does not replace Kubernetes DNS service discovery. Option C is too generic and implies a conventional threat-detection product rather than identity-based networking and policy enforcement.
Official references
Cilium eBPF Datapath Introduction , Introduction to Cilium and Hubble
Study Guide topic: Kernel hooks, endpoint policy, identities, and eBPF datapath enforcement.
