Kubernetes Networking Deep Dive

This is for you if

• You deploy to Kubernetes but guess when pods can't reach each other
• You're on call and want a real playbook for DNS, MTU and conntrack issues
• You're interviewing for platform, SRE or DevOps roles where networking questions go deep
• You need to choose or defend a CNI, kube-proxy mode or ingress strategy

What's inside

• The pod-to-Service journey walked step by step, with a mental model you can reuse in any incident
• Calico vs Cilium vs Flannel compared, and both Calico and Cilium installed on kind so you can see the difference on a node
• Every Service type, EndpointSlice conditions and the deploy-time termination race, with the fix
• kube-proxy iptables, nftables and ipvs status (ipvs deprecated, nftables GA and the planned default) plus Cilium's eBPF replacement
• CoreDNS and ndots:5 captured live on the wire, with tuning and NodeLocal DNSCache guidance
• Ingress vs Gateway API after the ingress-nginx retirement, with a canary HTTPRoute lab on Cilium
• NetworkPolicy default deny done right: DNS egress, the AND/OR selector trap and pod-port matching
• MTU and conntrack failures explained, a symptom-to-fix troubleshooting table and four worked incidents
• 26 senior-level interview Q&As, dense cheat sheets and a 30-day practice plan

After this guide you can

• Explain exactly what happens when a pod calls a Service, layer by layer
• Debug pods, nodes and flows with netshoot, tcpdump, conntrack and Hubble
• Read kube-proxy rules in iptables, nftables and eBPF and plan a move off ipvs
• Lock down namespaces with NetworkPolicy without breaking DNS or monitoring
• Route traffic with Gateway API and choose between overlay and native routing
• Diagnose MTU, conntrack and DNS latency problems that don't show up in kubectl

Contents

1. The mental modelp. 4
2. Pod networking and choosing a CNIp. 8
3. Services and EndpointSlicesp. 17
4. kube-proxy, nftables and eBPFp. 25
5. DNS: CoreDNS and ndotsp. 30
6. Getting traffic in: Ingress and Gateway APIp. 35
7. NetworkPolicyp. 40
8. MTU, conntrack and the quiet killersp. 45
9. Troubleshooting playbookp. 49
10. Production checklist and design decisionsp. 54
11. Interview questionsp. 57
12. Cheat sheetp. 64
13. 30-day practice planp. 68