Internet-Security.com TCP port 6443 details

TCP port 6443 is the default secure port for the Kubernetes API server (kube-apiserver).
kubeadm-based clusters, Rancher’s k3s, Rancher RKE/RKE2, and VMware Tanzu Kubernetes Grid expose the Kubernetes API on 6443 by default.
Red Hat OpenShift uses api.:6443 for its cluster API endpoint in standard installations.
In these systems, kubectl, kubelet, and controllers communicate with the API over HTTPS on 6443; HA setups often front multiple API servers on 6443 via a load balancer.
k3s servers listen on 6443, and k3s agents connect to the server on that port.
Security note: attackers routinely scan for exposed 6443 to find Kubernetes APIs; misconfigurations or weak authentication have led to cluster compromise and cryptomining deployments.

TCP 6443