No, not quite "made up". First thing is you want to know the IP address of your PC or Router, as that is what makes up your "LAN", as it is the device that controls the Network traffic.
Typically a "Default IP" for a LAN (Local Area Network) is 192.168.0.1 or 192.168.1.1, but to know for certain you use the PCs cmd to see what is being used by the PC. This also displays the actual PC's IP and you know not to use the exact same digits for the PS2.
Since the PS2 is not capable of self assigning an IP address, you MUST assign it Static in a configuration file, OPL provides that in its Settings screen.
So if your PC is 192.168.0.101, then you can use 192.168.0.10 to 192.168.0.100 or 192.168.0.102 to 192.168.0.254 for your PS2's IP.
If you have other PCs in your network LAN, then their IPs must also not be used for the PS2 or each other. The first 3 ocets make up your Network's identification to each PC or console that connects to your LAN, so the last ocet defines each PC/console individually.
Its like
192.168.0 is the street and
.101 is your house address number.
Hope that helps you a little bit to understand.
Look at my cmd picture i posted a few posts back, i use a router and the router controls the IP's traffic as a Gateway between each connected PC or console. My router is pre-configured as 192.168.1.1 and its starting IP number it assigns is 192.168.1.101 to the first connected PC that it detects. So if you turn on 3 PCs at once, the first will be 192.168.1.101, the second 192.168.1.102, the 3rd 192.168.1.103.
I have several PCs and several consoles that connect thru the router and i set some to Static so they are always the same and i set them higher than what the router will auto-assign any other PC/console. I set all the console to 192.168.1.200 or higher, as i know there isnt enough PCs to ever get that high in an auto-assigned IP number.
When you turn off your PC, its IP is now available to the router to re-assign the next one it detects is connected when you turn on another PC or console that is set for automatic IP. So you cant just 'set any number', you must be sure it wont get used by another connected device and make it static.