What is your IPAddress? http://whatismyipaddress.com/
This is the IP address for your router / network as far as the internet is concerned.
NOTE: this can change depending, but probably will not.
What is your Mac's IP Address? (System Preferences / Network / Ethernet)
This is the IP address of your computer as far as your router is concerned.
Is the IP address manually entered or determined by DHCP in your router?
NOTE: this can change if using DHCP, but probably will not.
Your router has to be set to forward requests from the internet to your computer.
If you are using Filemaker to access from outside your network,
Port 591 is registered for Filemaker
Someone outside your network opens Filemaker, chooses remote host
and in the IP address types "youripaddress:591" NOT "yourmacsipaddress:591"
Hope this helps a bit.
Never mind, I just reread the title of your post.
Have an appointment, will try to explain the IWP thing.
When you say you can access the database on your network, do you mean with Filemaker or a web browser?
If so what ipaddress:portnumber are you using internally?