mysqld api node (no replies)

Hi Guys

I setup mgm node and two data nodes and I put mysql node in mgm node, I have NDB 7.3 Redhat 6.6. When I do show command, data nodes connected but sql node node not. what is the issue?

Also if I want to fully test the cluster failover, what I have to do?? so from sql node do like : mysql -h data1 and data2, create a dummy database and tables then shutdown one node and add a row to table?? something like that?

Please clear these 2 things for me. many Thanks