implementing-network-policies-for-kubernetes

name	implementing-network-policies-for-kubernetes
description	Kubernetes NetworkPolicies provide pod-level network segmentation by defining ingress and egress rules that control traffic flow between pods, namespaces, and external endpoints. Combined with CNI plu
domain	cybersecurity
subdomain	container-security
tags	["containers","kubernetes","security","network-policies","microsegmentation"]
version	1.0
author	mahipal
license	Apache-2.0
nist_csf	["PR.PS-01","PR.IR-01","ID.AM-08","DE.CM-01"]

Implementing Network Policies for Kubernetes

Overview

Kubernetes NetworkPolicies provide pod-level network segmentation by defining ingress and egress rules that control traffic flow between pods, namespaces, and external endpoints. Combined with CNI plugins like Calico or Cilium, network policies enforce zero-trust microsegmentation to prevent lateral movement within the cluster.

When to Use

• When deploying or configuring implementing network policies for kubernetes capabilities in your environment
• When establishing security controls aligned to compliance requirements
• When building or improving security architecture for this domain
• When conducting security assessments that require this implementation

Common Misconfigurations & Verification

• No default-deny: NetworkPolicy is default-allow and additive. Without a podSelector: {} deny-all for Ingress and Egress per namespace, the allow rules below don't actually segment anything.
• CNI doesn't implement NetworkPolicy: plain flannel ignores NetworkPolicy objects, so kubectl apply succeeds but nothing is enforced. Confirm the CNI supports it (Calico, Cilium, Antrea) and that policies take effect.
• Egress deny without DNS allow: dropping egress without the kube-system UDP/TCP 53 rule breaks name resolution; operators then strip the egress policy, losing all egress control.
• Cloud metadata not blocked: an egress policy that doesn't except 169.254.169.254/32 (AWS/GCP) and 169.254.169.254/100.100.100.200 (Azure) leaves the SSRF→IMDS credential path open.
• Selector scope mistakes: podSelector: {} applies to the whole namespace (often intended for deny-all); a labelled selector with a typo silently matches no pods.
• Verify enforcement, not just creation: kubectl get netpol -n production, then a blocked test: kubectl run t --image=busybox --restart=Never -n production -- wget -qO- --timeout=2 http://db-svc:5432 must time out, while a correctly-labelled app=frontend pod reaches the backend.

Prerequisites

• Kubernetes cluster with NetworkPolicy-supporting CNI (Calico, Cilium, Antrea)
• kubectl configured with admin access
• Understanding of pod labels and selectors

Workflow

Step 1: Default Deny All Traffic