Open MPI can't launch remote nodes via SSH

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http://serverfault.com – I am trying to set up Open MPI between a few machines on out network. Open MPI works fine locally, but I just can't get it to work on a remote node. I can ssh into the remote machine (without password) just fine, but if I try something like mpiexec -n 4 --host remote.host hello_c then the ssh connection just times out. I checked several tutorials but the only configuration instructions they give is "make sure you can ssh into the remote machine without a password". I did and I still can't launch nodes on remote machines. What's the problem? (HowTos)