Port 6443: Kubernetes API
Port 6443 is the default port for the Kubernetes API server, the control-plane endpoint that kubectl and every cluster component talk to. Access to it is effectively access to the whole cluster, so it is normally protected with strong authentication and network policy.
| Port number | 6443 |
|---|---|
| Service | Kubernetes API server |
| Protocol | TCP |
| Category | Infrastructure & orchestration |
| Default encryption | No |
How do I check whether port 6443 is open?
Port 6443 carries TCP, so a connection either completes its handshake or it does not, which makes the check definitive.
| Question | Command | What to know |
|---|---|---|
| Is it open on a remote host? | nc -vz example.com 6443 | A TCP handshake either completes or it does not, so netcat gives a definitive answer in one line. |
| Same check on Windows | Test-NetConnection example.com -Port 6443 | Built into PowerShell. TcpTestSucceeded in the output is the answer; telnet is not installed by default on modern Windows. |
| What is listening locally? | ss -tlnp | grep ':6443 ' | Lists the process bound to port 6443 on Linux. On macOS use lsof -nP -iTCP:6443 -sTCP:LISTEN, on Windows netstat -ano | findstr :6443 |
Replace example.com with the host you are testing. A blocked port and a port with nothing listening on it look identical from the outside, so if a service should be running, check locally before blaming the firewall.
Frequently asked questions
What is port 6443 used for?
Port 6443 is the default port for the Kubernetes API server, the control-plane endpoint that kubectl and every cluster component talk to. Access to it is effectively access to the whole cluster, so it is normally protected with strong authentication and network policy.
Is port 6443 TCP or UDP?
Port 6443 (Kubernetes API) uses TCP.
Is port 6443 secure?
Port 6443 is not encrypted by default. Where possible, use an encrypted alternative or tunnel it over TLS or a VPN.
Should I open port 6443 on my firewall?
Only if you specifically need Kubernetes API. Expose it to the smallest set of trusted sources, and never open database or Windows-service ports to the whole internet.