So, I have a C3000-100NAS, which is not the exact same model as yours but this might help your situation as well. I currently have 3 systems, a PS4, PSTV, and PS Vita. The NAT issue only affects my gaming systems, everything else, like my laptop or phone, is unaffected. I ended up reading a lot of things online about opening up ports, putting IP addresses in the DMZ, etc. After playing around with the settings I accidentally figured out how this specific model works when it comes to porting.
Basically all you need to do is go into your settings and go into your advanced tab. From there you need to turn on the Universal Plug and Play (UPnP). This opens up one port that a gaming system can use to connect on a NAT 2 connection (I think mine uses TPS 34, both ways). After opening up the UPnP I suggest you either powercycle or do a soft reset on the modem-router. Once you turn it back on that one port will become available and your gaming system will automatically connect to a NAT 2 channel. Now, since it only has one port you can only connect one gaming system to it (regardless whether you're connected wireless or ethernet). If you connect a second gaming system while the one NAT 2 channel is already being used then the secondary system (and any other number of systems you connect) will automatically connect throug a NAT 3 channel.
I forget exact which section it is, but there should be a section that shows you which systems are connected through porting and which port number it is using. Your modem-router will lock on to whichever system you have on NAT 2. In order to switch the NAT 2 to another system you need to power off the current system then do a soft reset on the modem router, doing this disconnects the port number from the system. Once you turn the modem-router on the NAT 2 connection will be open again and then you'll be able to connect a new system to it. If you want to connect any other system you'll have to follow the same process. I hope this helps.
