Hi @pritamdamania87 ,
29400 is working because when I was using only one machine with hostname or ip(10.100.4.219 not 127.0.0.1),connection still timed out.
But I tried to downgrade pytorch version from 1.9.0 to 1.7.0, with almost the same settings, and used old torch.distributed.launch command,  the two nodes can do ddp train finally(2 times slower than only one node).