Technical explanation
Cilium can implement Layer 3 and Layer 4 forwarding exclusively through its eBPF datapath. IP, TCP, and UDP traffic can be routed, load-balanced, filtered, and redirected through eBPF programs attached to Linux networking hooks. These operations depend on network-layer addresses, protocols, ports, identities, and connection state; they do not require application-protocol parsing by a userspace proxy.
Application-layer operations are different. Cilium’s official Service Mesh architecture uses a proxy such as Envoy to parse HTTP, gRPC, and DNS when Layer 7 policy, observability, or traffic management requires understanding individual requests. The eBPF datapath transparently redirects selected traffic to the node-local proxy and retains identity context, while Envoy performs the protocol-aware operation.
Kafka parsing is also an application-layer activity rather than ordinary Layer 3 or Layer 4 forwarding. Moreover, current Cilium releases removed the former Envoy Go extension mechanism used for Kafka and generic proxylib rules, further reinforcing that it is not an eBPF-only forwarding case.
Therefore, D accurately identifies the scenario in which the Service Mesh datapath can remain entirely in the kernel without requiring Envoy.
Official references
Cilium Service Mesh ; eBPF Datapath Introduction .
Study Guide topic: Service Mesh.
