There are 3 Nat Types !
Nat Type 1 means connected directly to the internet without a router !
Nat Type 2 means you're connected through a router properly with no issues !
Nat Type 3 means Connected through a router without open ports or DMZ setup for PS4. Everything should function properly, but you may have connection, voice chat or other issues.
In order to open up your NAT on your PS4 you will need to make an adjustment on your PS4 and on your router. First you will want to set up your PS4 for a static IP address. This means turning off DHCP and assigning your PS4 a single, static IP address. Before you start this process head over to the network tab on the XMB and choose "Internet Connection Status." From here note your current IP address, your subnet mask, your default router and primary and secondary DNS settings. Write these down, you will need them in the following steps.
Now visit Internet Connection Settings ! Remember the settings you wrote down from your status page? You will need them here. You will have to enter in the static IP Address you want to assign to your PS4, the Subnet Mask (which is usually 255.255.255.0), the default router (the IP address of your router, most often 192.168.1.1 or 192.168.100.1), and the Primary and Secondary DNS settings. You will have to input all of these numbers.
Please NOTE - You will want to set the last number of your IP address high enough that other wireless or wired items on your network will not be assigned the same number through DHCP. While DHCP had chosen .3 as an IP address for my PS4 initially, I bumped it up to .23 because I have less than 23 items in my network. If you do not have DHCP enabled on your router, you do not need to worry about this and can simply choose an IP address that does not conflict with your other devices and which is available through your router.
Once you have all of the settings input, you need to save them. Your settings will change and the PS4 will offer to perform an Internet Connection Test for you. If you let it do the test now chances are you will still get a Type 3 NAT connection.
In addition to making the necessary changes on your PS4, you will also have to open up some ports on your router. The ports you need to open are: TCP: 80, 443, 5223 UDP: 5223, 3478, 3479, 3658
Go to your default routers setting, By typing in your Routers IP address in URL Box - linksys's default is 192.168.1.1 and Username is blank, Password is Admin
Once you have forwarded these ports and saved your settings its a good idea to unplug and plug back in your router. This will refresh everything on your network connected to your router. Once done head back to your PS4 and perform an Internet Connection Test.