You have
Blue Iris installed on a Windows machine in your house, right?
This web site explains rather roughly how to do port forwarding with an Arris router. Beware the portforward.com web site tries to get you to buy their software, but
don't do it. You don't need it. You'll be fine with just the freely provided information.
http://portforward.com/english/routers/port_forwarding/Arris/WTM552G/Blue_Iris.htm
Ignore the part where it says to forward ports 80 and 81. Blue Iris only needs one port to be forwarded. I recommend port 80 because that is the default port for HTTP; just make sure it is also configured in Blue Iris Options. The Blue Iris options window will tell you what port you have to forward and it will also tell you the LAN address that you must forward to. In this example the port is 80 and the LAN address is 192.168.0.132.
That should give you all the information you need to set up a port forwarding rule. Once you have the port forwarding rule set up, you need to be aware that you have a public IP address and a local IP address. You'll need to connect to the public IP address when you are away from home. When you are at home, you can connect to the local IP address. The Blue Iris Android app has fields for both addresses so you don't need to constantly change between them. You can find out what your public IP address is by looking in the Blue Iris options as seen above (I censored my public IP in the screenshot for privacy reasons). Or if that doesn't work, the portforward.com site should have your public IP address in the upper right corner of the page.
If you discover that your public IP address changes regularly, you will need to set up a free dynamic DNS account from one of the many providers that offer this free service. I recommend you check your router's interface for a
DDNS or Dynamic DNS section because most routers have a list of supported dynamic DNS services and not all of the services are compatible with all routers.
