Thank you Nabruk, your solution worked. I bought the ATV 4 two months ago and downloaded Netflix app and since then I kept getting the same error 11800 when I tried to play any content. I tried each and every trouble shooting steps that Netflix, Apple, my ISP & other forums recommended and none fixed the problem. Until I came across this forum while searching for answers and tried your solution. Changing the DNA manually to a similar DNS setting of other device I had connected to my WiFi network worked just fine.
Great to hear, thank you for the feedback!