15. Why does distributed mode not work on my MacOS X computer?

VisIt can run all of its components locally, or it can run some of them on remote computers. When the compute engine and metadata server are run on a remote computer, VisIt is said to be running in distributed mode. When VisIt runs in distributed mode, it attempts to launch some of its components on remote computers, and those programs then talk to VisIt via socket communication. Assuming that you have an account on the remote computer and VisIt is installed there, you should be able to run in distributed mode. If you have everything set up properly and distributed mode still does not work, you should check your firewall settings. MacOS X has an integrated firewall program that disallows remote programs from making inbound connections to programs running on your Mac. You either need to disable your firewall or change its settings so ports 5600 through 5605 (VisIt's ports) are not blocked. Once you change your firewall settings, VisIt components running on remote computers will be able to connect back to the Mac and distributed mode will work.

VisIt FAQ