How to troubleshoot "unable to login to cluster through *.apps load balancer"

Issue

• Unable to login through the API load balancer endpoints (e.g. oc login https://api_cluster_url:6443), When the DNS configured to point directly to the nodes where router resides, able to login within the cluster itself on the master node.

• [root@master01 ~]# oc login https://api_cluster_url:6443
  error: dial tcp xx.xx.xx.xx:6443: i/o timeout - verify you have provided the correct host and port and that the server is currently running.