If you’re behind a wireless router, Apple Airport or some other kind of router with a firewall, you will probably need to enable port forwarding for the port you want to use to allow remote access to your Mac or Mac server. iStat Server uses port 5109 as its default port.
If you’re monitoring several computers on the same network remotely, then you’ll probably want to set up port forwarding so that each computer has its own port. For example, you might have port forwarding from port 5109 to 5109 going to the IP address of your first computer, port 5110 to 5109 going to the IP address of your second computer and port 5112 to 5109 going to the IP address of your third computer (you’ll also need to ensure you’re using static IP addresses for your computers).
If you have different public and private ports, then the public port should be entered into the iStat iPhone app and the private port should be entered into iStat Server.
Please note that we aren’t able to provide instructions for every router, but information should be easy to find online or in your router's manual. The links below should help get you on the right path.
Instructions for Airport Extreme — Forward a Port Using Your Airport Extreme, iclarified.com.
Instructions for other routers — Please visit this page on portforward.com for more information on port forwarding for some common routers.