I am curious about this. I see occasionally it spoke of but have never attempted to do it.
To start with, port forwarding (it has other names too on different router makes/models) is only needed if you want to access a device sitting on your local network from a remote device (ie that's external to your local network). It's completely unnecessary simply to talk from one device to another
within your local network (or, more strictly, local subnet AIUI).
The only device that an external server/PC can talk to directly if it tries to initiate contact with your network is the Internet router. So there has to be some mechanism by which an external request to the router can be passed on ('forwarded') to the device within your local network that you actually want to talk to, ie the WLIP logger in this example. This is achieved by making a request to the router on a specific port number and then there has to be a rule set up on the router so that it knows that such an incoming request be forwarded to the specific device, ie a logger here. It's unwise in general to set up such rules for eg a PC on your network because that could potentially give an external hacker access to your complete network, but for such a limited device as an IP logger it's unlikely that much damage could be done AIUI.
The exact process of setting up the port forwarding rule in your router settings varies from router to router. so it's difficult to describe in general. Like a lot of things, it's usually quite easy to do once you've got your head around the concepts, but something of a learning curve at the first time of asking. But almost certainly easier than you're imagining!
NB Not pretending to be a network expert here - others might be able to add more detail or qualifications.
Edit: I probably should have added that this process for external access works most easily if your router has a fixed
external IP address. (I'm not talking about the IP address on your internal network, but the IP assigned by your ISP to your router.) There may also be ways of enabling external access if you don't have a fixed external IP address but these will likely be more complicated to set up in the absence of a fixed IP address.