Cilium Network Policy Review

Cilium Network Policy Review

Purpose

Review Cilium policy resources against zero-trust correctness, blast radius, and the operational traps unique to eBPF-backed networking. Cilium's policy surface is broader than native Kubernetes NetworkPolicy — CiliumNetworkPolicy adds L7 rules, FQDN matching, ICMP control, and identity-based selectors; CiliumClusterwideNetworkPolicy applies cluster-wide; CiliumEgressGatewayPolicy controls SNAT egress IPs; and policy-default-local-cluster changes how policy evaluates across ClusterMesh.

Lean operating rules

• Prefer live cluster evidence (kubectl get networkpolicies,ciliumnetworkpolicies,ciliumclusterwidenetworkpolicies,ciliumegressgatewaypolicies -A -o yaml, cilium policy get, cilium clustermesh inspect-policy-default-local-cluster, and Hubble flow observation) when the active client exposes it; otherwise fall back to official Cilium documentation (docs.cilium.io) and sanitized YAML.
• Separate confirmed facts from inference. If Cilium agent state, ClusterMesh peer status, or Hubble flow data was not queried, say so.
• Treat removal of a default-deny NetworkPolicy in a namespace as a critical finding — pods become reachable from any source/destination unless another policy provides isolation.
• Treat CiliumNetworkPolicy egress with toCIDRSet: [{cidr: 0.0.0.0/0}] (no except for sensitive CIDRs) as a critical finding — unrestricted egress is a documented data exfiltration path.
• Treat any change to policy-default-local-cluster in a ClusterMesh deployment as critical-blast-radius — every existing policy's cross-cluster semantics flip simultaneously.
• Challenge CiliumEgressGatewayPolicy with the same egressIP used in two policies — silent connection breakage when both match.
• Challenge L7 rules in CiliumNetworkPolicy for namespaces where Envoy proxy is not enabled — L7 fields require the proxy.
• Keep the answer scoped, reversible, least-privilege, and explicit about blockers or unknowns.

References

Load these only when needed:

• Evidence path and tooling — use when choosing live cluster evidence, confirming Cilium version and ClusterMesh state, or switching to documentation mode.
• Workflow and output contract — use when executing the full review, applying stress checks across the three policy formats and ClusterMesh, or formatting the final answer.
• Official sources — use when you need the detailed Cilium documentation list, CRD schema, and grounded insights.

Response minimum

Return, at minimum:

• the scoped target (namespace NetworkPolicy, namespace CiliumNetworkPolicy, cluster-wide CiliumClusterwideNetworkPolicy, CiliumEgressGatewayPolicy) and evidence level,
• the default-deny posture in the affected namespace(s),
• the L7 enforcement assessment (Envoy proxy enabled / required) and whether L7 rules will actually run,
• the ClusterMesh assessment when applicable (policy-default-local-cluster semantics),
• the safest next actions and rollback plan,
• the assumptions or blockers that prevent stronger conclusions.