Confusion over 'ssh' command for networking

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Dear All,

I am trying to create a ROS network between two computers. The computer A as master (userA@ComputerNameA:~$) and computer B as client (userB@ComputerNameB:~$). I also set ROS Environment Variables as follow.

On Computer A: export ROS_HOSTNAME= ComputerNameA export ROS_MASTER_URI=http://ComputerNameA:11311

On Computer B: export ROS_HOSTNAME=ComputerNameB export ROS_MASTER_URI=http://ComputerNameA:11311

My problem is when I want to test the network connectivity by SSH command before using ROS packages I get confused and don't know which command I must run on which computer, Master or Client?

For example, If I must run the ssh command on master (computer A), which one of these commands is correct?

1- (userA@ComputerNameA:~$) ssh userA@ComputerNameB or 2- (userA@ComputerNameA:~$) ssh userB@ComputerNameB

Thanks...