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## VisIt's ports

VisIt uses secure shell (ssh) to launch its components on remote computers. Secure shell often uses port 22 but if you are attempting to communicate with a computer that does not use port 22 for ssh then you can specify a port for ssh by clicking the Specify port check box and then typing a new port number into the adjacent text field.

One common case of when you might want to use a different port is if you are running VisIt on your home computer and connecting to an LLNL computer via Internet Port Allow (IPA), which allows your computer through the Lab firewall so it is possible to connect to some computers from offsite. In this type of connection, the port for ssh is often 822 so in order to successfully connect VisIt from your home desktop to an LLNL computer, you would specify port 822 in the Advanced options tab.

In addition to relying on remote computers' ssh port, VisIt listens on its own ports (5600-5605) while launching components. If your desktop computer is running a firewall that blocks ports 5600-5605 then any remote components that you launch will be unable to connect back to the viewer running on your local computer. If you are not able to successfully launch VisIt components on remote computers, be sure that you make sure your firewall does not block VisIt's ports. Windows XP's and MacOS X's default software firewall configurations block VisIt's ports so if you run those software firewall programs, you will have to unblock VisIt's ports if you want to run VisIt in distributed mode.