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devopscritical PriorityID: cilium-ebpf-host-routing-ephemeral-port-standard

Cilium eBPF Host-Routing NodePort Ephemeral Port Allocation Standard

Enforces strict coordination between Linux kernel ephemeral port ranges (ip_local_port_range) and Cilium eBPF host-routing NodePort configurations. Under ultra-high-throughput microservice topologies, port collision or conntrack table saturation triggers silent packet drops unless Cilium bypasses the legacy netfilter/conntrack subsystem via eBPF host routing (bpf.masquerade=true, bpf.hostRouting=true) and non-overlapping NodePort allocation.

Prohibited Anti-Pattern: Overlapping Linux Ephemeral Port Range with Kubernetes NodePort Port Range while Legacy Conntrack Remains Unbypassed

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---
description: Cilium eBPF Host-Routing NodePort Ephemeral Port Allocation Standard - Enforces strict coordination between Linux kernel ephemeral port ranges (ip_local_port_range) and Cilium eBPF host-routing NodePort configurations. Under ultra-high-throughput microservice topologies, port collision or conntrack table saturation triggers silent packet drops unless Cilium bypasses the legacy netfilter/conntrack subsystem via eBPF host routing (bpf.masquerade=true, bpf.hostRouting=true) and non-overlapping NodePort allocation.
globs: **/values*.yaml, **/cilium*.yaml, **/sysctl*.conf, **/daemonset*.yaml, terraform/**/*.tf
alwaysApply: true
verified_by: "agentrules.org"
license: "CC-BY-4.0"
source: "https://agentrules.org/rules/cilium-ebpf-host-routing-ephemeral-port-standard"
---

# Cilium eBPF Host-Routing NodePort Ephemeral Port Allocation Standard

> **Severity**: CRITICAL | **Category**: devops
> **Anti-Pattern Warning**: Overlapping Linux Ephemeral Port Range with Kubernetes NodePort Port Range while Legacy Conntrack Remains Unbypassed

## System Constraints
You are a Principal Platform Engineer enforcing strict network topology integrity for Cilium eBPF host-routing and NodePort ephemeral port allocation. You must ensure that Cilium values files, Terraform infrastructure manifests, and Linux node sysctl configurations explicitly decouple net.ipv4.ip_local_port_range from the NodePort port range (typically 30000-32767). You must enforce eBPF host routing flags (bpf.masquerade=true, bpf.hostRouting=true, kubeProxyReplacement=true) to bypass Linux conntrack bottlenecks, prevent silent socket starvation, and eliminate race conditions during high-concurrency ephemeral SNAT translations.

## Strict Guidelines
- Engineers MUST ALWAYS configure Linux kernel sysctl net.ipv4.ip_local_port_range to end strictly below the Kubernetes NodePort allocation range (e.g., '10240 29999' when NodePort uses 30000-32767).
- Engineers MUST NEVER allow default Linux sysctl net.ipv4.ip_local_port_range ('32768 60999') to overlap with or immediately flank dynamic NodePort services without explicit reservation.
- Engineers MUST configure Cilium Helm values with 'kubeProxyReplacement=true', 'bpf.masquerade=true', and 'bpf.hostRouting=true' to bypass kernel netfilter and iptables connection tracking overhead.
- Cilium manifests MUST set 'devices' explicitly (e.g., 'devices: "{eth0,eth1}"') to ensure eBPF programs attach to physical interfaces and properly handle TC (traffic control) host routing bypass.
- Host initialization scripts MUST verify conntrack bypass and ephemeral port reservation before Kubernetes worker nodes report Ready.

## Bad vs Good Implementations
### Cilium Helm Configuration and Node Sysctl Definition

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: Operating in partial kube-proxy replacement mode without eBPF masquerading forces packets through Linux netfilter conntrack. When combined with default sysctl ephemeral port settings, high-throughput microservice mesh traffic suffers silent SNAT table collisions and socket dropouts.
```yaml
# Anti-Pattern: Unspecified host-routing relies on legacy conntrack with overlapping dynamic ports
kubeProxyReplacement: "partial"
bpf:
  masquerade: false
  hostRouting: false
nodePort:
  range: "30000,32767"
# Host kernel sysctl left at default: net.ipv4.ip_local_port_range = 32768 60999
# High connection churn causes conntrack table exhaustion and silent packet drops.
```

#### Production Standard (Correct)
> **Standard**: Explicitly enabling bpf.hostRouting and bpf.masquerade alongside strict segregation between net.ipv4.ip_local_port_range (10240-29999) and NodePorts (30000-32767) eliminates kernel conntrack lock contention and guarantees zero packet drops under ultra-high-throughput workloads.
```yaml
# Invariant: Native eBPF Host Routing with strict port partition
kubeProxyReplacement: "true"
bpf:
  masquerade: true
  hostRouting: true
  tproxy: true
devices: "+eth+"
nodePort:
  range: "30000,32767"
  autoProtectPortRanges: true
# Paired Host Sysctl Manifest (applied via DaemonSet/MachineConfig):
# net.ipv4.ip_local_port_range = 10240 29999
# net.core.somaxconn = 65535
```
Recommended MCP Servers (mcp-serverlist.com)

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

Kubernetes Cluster Inspector MCP
Inspects running Cilium DaemonSets, ConfigMaps, and node sysctl settings directly within the cluster.
Recommended Agent Skills (askills.dev)

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

Cilium CLI Diagnostic Suite
Executes 'cilium bpf nat list' and 'cilium status --verbose' to audit eBPF map sizing, connection tracking bypass, and node port tables.
Architectural Specification & Invariant Rationale

Architectural Invariant Design: Cilium eBPF Host-Routing NodePort Ephemeral Port Allocation Standard

Cilium eBPF Host-Routing NodePort Ephemeral Port Allocation Standard defines an industrial-grade behavioral standard for devops engineering. Enforces strict coordination between Linux kernel ephemeral port ranges (ip_local_port_range) and Cilium eBPF host-routing NodePort configurations. Under ultra-high-throughput microservice topologies, port collision or conntrack table saturation triggers silent packet drops unless Cilium bypasses the legacy netfilter/conntrack subsystem via eBPF host routing (bpf.masquerade=true, bpf.hostRouting=true) and non-overlapping NodePort allocation. 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: Overlapping Linux Ephemeral Port Range with Kubernetes NodePort Port Range while Legacy Conntrack Remains Unbypassed 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 DriftOverlapping Linux Ephemeral Port Range with Kubernetes NodePort Port Range while Legacy Conntrack Remains UnbypassedCritical
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 configure Linux kernel sysctl net.ipv4.ip_local_port_range to end strictly below the Kubernetes NodePort allocation range (e.g., '10240 29999' when NodePort uses 30000-32767).

Engineers MUST ALWAYS configure Linux kernel sysctl net.ipv4.ip_local_port_range to end strictly below the Kubernetes NodePort allocation range (e.g., '10240 29999' when NodePort uses 30000-32767).

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 NEVER allow default Linux sysctl net.ipv4.ip_local_port_range ('32768 60999') to overlap with or immediately flank dynamic NodePort services without explicit reservation.

Engineers MUST NEVER allow default Linux sysctl net.ipv4.ip_local_port_range ('32768 60999') to overlap with or immediately flank dynamic NodePort services without explicit reservation.

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 configure Cilium Helm values with 'kubeProxyReplacement=true', 'bpf.masquerade=true', and 'bpf.hostRouting=true' to bypass kernel netfilter and iptables connection tracking overhead.

Engineers MUST configure Cilium Helm values with 'kubeProxyReplacement=true', 'bpf.masquerade=true', and 'bpf.hostRouting=true' to bypass kernel netfilter and iptables connection tracking overhead.

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

Cilium manifests MUST set 'devices' explicitly (e.g., 'devices

Cilium manifests MUST set 'devices' explicitly (e.g., 'devices: "{eth0,eth1}"') to ensure eBPF programs attach to physical interfaces and properly handle TC (traffic control) host routing bypass.

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

Host initialization scripts MUST verify conntrack bypass and ephemeral port reservation before Kubernetes worker nodes report Ready.

Host initialization scripts MUST verify conntrack bypass and ephemeral port reservation before Kubernetes worker nodes report Ready.

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 NodePort Ephemeral Port Allocation Standard critical for AI coding assistants?

Enforces strict coordination between Linux kernel ephemeral port ranges (ip_local_port_range) and Cilium eBPF host-routing NodePort configurations. Under ultra-high-throughput microservice topologies, port collision or conntrack table saturation triggers silent packet drops unless Cilium bypasses the legacy netfilter/conntrack subsystem via eBPF host routing (bpf.masquerade=true, bpf.hostRouting=true) and non-overlapping NodePort allocation. 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 (Overlapping Linux Ephemeral Port Range with Kubernetes NodePort Port Range while Legacy Conntrack Remains Unbypassed) 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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