For DEX, this is what I do. I directly connect my ethernet from my laptop to the back of my PS3. I set up my laptop to use a wifi connection. Then I share that wifi connection to the ethernet connection. (Windows only.) I have my PS3 set up to use "Wired" as the main connection then I use the IPv4 address of the ethernet connection as the default gateway for the PS3, same for DNS. Once that's done, I test the connection and the PS3 will automatically pull an IP address from the laptop and use it as it's own. If the connection test passes, then you should be able to connect to the internet on your PS3.
I recommend you have ProDG Target Manager installed so you can test the connection between the console and the computer.
Example:
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