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devopscritical PriorityID: cilium-wireguard-bpf-host-routing-fence

Cilium eBPF Host-Routing WireGuard Cryptographic Invariant Fence

Enforces strict cryptographic routing invariants between Cilium eBPF host-routing and WireGuard tunnel encapsulation layers. Prevents BPF tc-redirect and socket layer short-circuits from bypassing virtual encryption devices (cilium_wg0) and leaking unencrypted cross-tenant payload frames over raw host interfaces.

Prohibited Anti-Pattern: Enabling BPF Direct Host Routing with WireGuard Without Cryptographic Fallback Isolation

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---
description: Cilium eBPF Host-Routing WireGuard Cryptographic Invariant Fence - Enforces strict cryptographic routing invariants between Cilium eBPF host-routing and WireGuard tunnel encapsulation layers. Prevents BPF tc-redirect and socket layer short-circuits from bypassing virtual encryption devices (cilium_wg0) and leaking unencrypted cross-tenant payload frames over raw host interfaces.
globs: infra/**/*.ts, deploy/**/*.ts, k8s/**/*.ts, clusters/**/*.ts
alwaysApply: true
verified_by: "agentrules.org"
license: "CC-BY-4.0"
source: "https://agentrules.org/rules/cilium-wireguard-bpf-host-routing-fence"
---

# Cilium eBPF Host-Routing WireGuard Cryptographic Invariant Fence

> **Severity**: CRITICAL | **Category**: devops
> **Anti-Pattern Warning**: Enabling BPF Direct Host Routing with WireGuard Without Cryptographic Fallback Isolation

## System Constraints
You are a Principal Infrastructure & Security Architect enforcing strict cryptographic routing boundaries in eBPF-driven Kubernetes platforms. When deploying Cilium with WireGuard encryption, native BPF host-routing (bpf.hostRouting=true) can short-circuit the Linux network stack and bypass the cilium_wg0 interface, directly dispatching unencrypted tenant sk_buffs onto physical network adapters. You must mandate deterministic infrastructure invariants ensuring host-routing is safely gated or node-to-node WireGuard encryption fences are unbypassable.

## Strict Guidelines
- Engineers MUST ALWAYS explicitly evaluate the kernel compatibility matrix before enabling 'bpf.hostRouting=true' alongside 'encryption.type=wireguard'.
- Engineers MUST set 'encryption.nodeEncryption: true' whenever WireGuard is activated to prevent host-to-host pod payloads from evading the encryption envelope.
- Engineers MUST set 'bpf.hostRouting: false' on Linux kernel baselines below 5.19 to guarantee all pod-to-pod cross-node traffic traverses the Linux network stack into 'cilium_wg0'.
- Infrastructure definitions MUST configure 'strict' encryption mode ('encryption.wireguard.strictMode: true') or validate that unencrypted egress traffic matching internal CIDRs is rejected at the physical NIC via BPF filters.
- Engineers MUST NOT deploy Cilium configurations with native routing mode ('routingMode: native') and WireGuard without validating cryptographic tunnel device enforcement.
- Security definitions MUST deploy CiliumNetworkPolicies with explicit egress assertions guaranteeing inter-tenant traffic cannot transition through host network namespace namespaces without cryptographic encapsulation.

## Bad vs Good Implementations
### Cilium Helm Release Definition in Pulumi / CDK8s

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: Enabling bpf.hostRouting alongside WireGuard with nodeEncryption disabled causes BPF tc egress programs on pod veth interfaces to execute fib_lookup and redirect packets directly to physical netdevs, bypassing the virtual cilium_wg0 device and exposing tenant payloads in cleartext.
```typescript
import * as k8s from "@pulumi/kubernetes";

// ANTI-PATTERN: Native BPF host routing bypasses the Linux stack and cilium_wg0,
// leaking unencrypted cross-node pod traffic out the physical NIC.
export const ciliumRelease = new k8s.helm.v3.Release("cilium", {
  chart: "cilium",
  repositoryOpts: { repo: "https://helm.cilium.io/" },
  namespace: "kube-system",
  values: {
    routingMode: "native",
    bpf: {
      masquerade: true,
      hostRouting: true, // Fatal: BPF short-circuits socket routing directly to eth0 without WireGuard encapsulation
    },
    encryption: {
      enabled: true,
      type: "wireguard",
      nodeEncryption: false, // Fatal: Node-to-node and host-originating traffic remains completely plaintext
    },
  },
});
```

#### Production Standard (Correct)
> **Standard**: By disabling unvalidated BPF host routing (or enforcing kernel-aware strict fencing) and mandating nodeEncryption with wireguard.strictMode=true, all inter-node pod frames are forced through cilium_wg0 before egressing physical interfaces, eliminating plaintext tenant data leaks.
```typescript
import * as k8s from "@pulumi/kubernetes";

// PRODUCTION INVARIANT: Cryptographically guarded eBPF host routing fence
export const ciliumRelease = new k8s.helm.v3.Release("cilium", {
  chart: "cilium",
  repositoryOpts: { repo: "https://helm.cilium.io/" },
  namespace: "kube-system",
  values: {
    routingMode: "native",
    bpf: {
      masquerade: true,
      // Kernel stack traversal required for strict WireGuard encapsulation boundary
      hostRouting: false,
    },
    encryption: {
      enabled: true,
      type: "wireguard",
      nodeEncryption: true,
      wireguard: {
        strictMode: true,
        // Ensures non-encrypted pods cannot transmit packets outside the cryptographic fence
        fallbackToHostRoutes: false,
      },
    },
    tunnelProtocol: "none",
    devices: ["eth0", "cilium_wg0"],
  },
});
```
Recommended MCP Servers (mcp-serverlist.com)

Equip agent with system tools to verify code for this stack.

Kubernetes Context Inspector
Inspects running Cilium Helm values, DaemonSet configurations, and active node BPF maps to detect encryption bypass leaks.
Recommended Agent Skills (askills.dev)

Ready-to-use executable skill functions tailored to this stack.

Cilium CLI & BPF Verifier
Executes 'cilium bpf tunnel list', 'cilium status --verbose', and bpftool inspections to verify cryptographic device routing invariants.
Architectural Specification & Invariant Rationale

Architectural Invariant Design: Cilium eBPF Host-Routing WireGuard Cryptographic Invariant Fence

Cilium eBPF Host-Routing WireGuard Cryptographic Invariant Fence defines an industrial-grade behavioral standard for devops engineering. Enforces strict cryptographic routing invariants between Cilium eBPF host-routing and WireGuard tunnel encapsulation layers. Prevents BPF tc-redirect and socket layer short-circuits from bypassing virtual encryption devices (cilium_wg0) and leaking unencrypted cross-tenant payload frames over raw host interfaces. Modern software architectures require strict adherence to deterministic patterns to guarantee high availability, maintainability, and zero security vulnerabilities.

Framework Paradigm Shift & Drift MechanicsLLMs are trained on millions of open-source repositories containing outdated code, legacy idioms, and unpatched antipatterns. When coding assistants generate implementations for this stack, they default to common statistical tokens: Enabling BPF Direct Host Routing with WireGuard Without Cryptographic Fallback Isolation Without an explicit system instruction file, developers spend hours debugging silent failures.
Failure Modes & Production Blast Radius

Hazard Analysis: What Breaks Without This Rule

The following failure modes have been cataloged from hundreds of hours of production code reviews where AI assistants produced non-compliant implementations:

Failure ModeAI Symptom (The Anti-Pattern)SeverityProduction Impact & Remedy
AI Hallucination & Deprecation DriftEnabling BPF Direct Host Routing with WireGuard Without Cryptographic Fallback IsolationCritical
Violating this industrial standard introduces regression bugs, security risks, and unexpected runtime failures in production.
Enforce explicit behavioral system directives across all AI coding assistants in your repository.
Silent Architecture InconsistencyAI assistants produce mixed paradigms across files, creating fragmented codebase conventions.Medium
Increases cognitive load during code reviews and leads to maintenance debt across engineering teams.
Pin project conventions in .cursor/rules, CLAUDE.md, and AGENTS.md so all team agents follow identical guardrails.
Architectural Directives in Detail

Step-by-Step Production Directives

Each rule constraint below is injected into the AI agent's system prompt to establish deterministic boundaries:

1

Engineers MUST ALWAYS explicitly evaluate the kernel compatibility matrix before enabling 'bpf.hostRouting=true' alongside 'encryption.type=wireguard'.

Engineers MUST ALWAYS explicitly evaluate the kernel compatibility matrix before enabling 'bpf.hostRouting=true' alongside 'encryption.type=wireguard'.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
2

Engineers MUST set 'encryption.nodeEncryption

Engineers MUST set 'encryption.nodeEncryption: true' whenever WireGuard is activated to prevent host-to-host pod payloads from evading the encryption envelope.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
3

Engineers MUST set 'bpf.hostRouting

Engineers MUST set 'bpf.hostRouting: false' on Linux kernel baselines below 5.19 to guarantee all pod-to-pod cross-node traffic traverses the Linux network stack into 'cilium_wg0'.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
4

Infrastructure definitions MUST configure 'strict' encryption mode ('encryption.wireguard.strictMode

Infrastructure definitions MUST configure 'strict' encryption mode ('encryption.wireguard.strictMode: true') or validate that unencrypted egress traffic matching internal CIDRs is rejected at the physical NIC via BPF filters.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
5

Engineers MUST NOT deploy Cilium configurations with native routing mode ('routingMode

Engineers MUST NOT deploy Cilium configurations with native routing mode ('routingMode: native') and WireGuard without validating cryptographic tunnel device enforcement.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
6

Security definitions MUST deploy CiliumNetworkPolicies with explicit egress assertions guaranteeing inter-tenant traffic cannot transition through host network namespace namespaces without cryptographic encapsulation.

Security definitions MUST deploy CiliumNetworkPolicies with explicit egress assertions guaranteeing inter-tenant traffic cannot transition through host network namespace namespaces without cryptographic encapsulation.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
Technical Questions & Answers

Frequently Asked Technical Questions

Common questions developers face when configuring AI coding assistants for this stack:

Q:Why is Cilium eBPF Host-Routing WireGuard Cryptographic Invariant Fence critical for AI coding assistants?

Enforces strict cryptographic routing invariants between Cilium eBPF host-routing and WireGuard tunnel encapsulation layers. Prevents BPF tc-redirect and socket layer short-circuits from bypassing virtual encryption devices (cilium_wg0) and leaking unencrypted cross-tenant payload frames over raw host interfaces. Without explicit behavioral boundaries, AI coding assistants (Cursor, Claude Code, Windsurf, Codex) rely on training data averages, which frequently produce deprecated, inefficient, or vulnerable code patterns.

Q:How does adopting this rule prevent AI hallucinations?

This rule explicitly declares what the AI must avoid (Enabling BPF Direct Host Routing with WireGuard Without Cryptographic Fallback Isolation) and prescribes verified positive examples. Grounding the LLM with negative and positive pairs eliminates guesswork.

Q:Which AI coding environments are supported?

This specification is multi-platform compatible: Cursor (.cursor/rules/*.mdc & .cursorrules), Anthropic Claude Code (CLAUDE.md), Windsurf (.windsurfrules), Codex / Cline (AGENTS.md), and GitHub Copilot (.github/copilot-instructions.md).

Q:Can I combine this rule with other technology stacks?

Yes. Use the Interactive Stack Builder or download an Agent Pack to merge this rule with other frontend, backend, database, security, and DevOps rules without syntax collision.

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