Port 6443 (TCP) — Kubernetes API Server
TCP/6443 is the standard TLS-encrypted HTTPS port exposed by kube-apiserver for kubectl administrators, kubelet worker nodes, controllers, and CI/CD deployers.
| Port Number | 6443 |
|---|---|
| Transport Protocol | TCP |
| Primary Service | Kubernetes API Server |
| Standard / Specification | HTTPS / Kubernetes REST |
| IANA Port Range | Registered User Port (1024–49151) |
| Internet Exposure Risk | Cluster control-plane gateway; restrict public endpoint CIDRs and enforce RBAC + short-lived OIDC tokens. |
Firewall Architecture & Hardening Best Practices
On managed EKS/GKE/AKS or kubeadm clusters, prefer private API endpoints reachable over VPN, or configure strict control-plane authorized network CIDR allowlists on TCP/6443.
Operational Troubleshooting Note
Worker nodes require outbound TCP/6443 to register kubelets and watch pod specs—verify this rule first if nodes stay NotReady.
Quick CLI Connectivity & Firewall Reference
# Test TCP/6443 reachability (Linux / macOS / PowerShell) nc -zv target.example.com 6443 Test-NetConnection -ComputerName target.example.com -Port 6443 # Allow restricted CIDR on Linux UFW firewall ufw allow from 10.0.0.0/8 to any port 6443 proto tcp
Planning firewall allowlists or VPN overlays? Use our IPv4 CIDR Calculator, MTU & TCP MSS Calculator, or WireGuard AllowedIPs Generator.
Browse Common Network & Cloud Ports
Port 22 (SSH) Port 25 (SMTP Mail Relay) Port 53 (Domain Name System) Port 67 (DHCPv4 Server) Port 80 (HTTP Web Traffic) Port 123 (Network Time Protocol) Port 161 (SNMP Polling) Port 179 (Border Gateway Protocol) Port 389 (LDAP Directory) Port 443 (HTTPS & HTTP) Port 445 (SMB Direct File Sharing) Port 465 (SMTPS Implicit TLS Submission) Port 500 (IPsec IKEv2 Key Exchange) Port 514 (Syslog Telemetry) Port 587 (SMTP Mail Submission) Port 636 (LDAPS) Port 853 (DNS over TLS) Port 993 (IMAPS Encrypted Mailbox) Port 1194 (OpenVPN Tunnel) Port 1433 (Microsoft SQL Server) Port 1812 (RADIUS Authentication) Port 2049 (Network File System) Port 2379 (etcd Client API) Port 3306 (MySQL & MariaDB) Port 3389 (Remote Desktop Protocol) Port 4500 (IPsec NAT Traversal) Port 5432 (PostgreSQL Database) Port 6379 (Redis) Port 6443 (Kubernetes API Server) Port 51820 (WireGuard VPN)