I have nearly the same problem as [Set Open DNS in Android 5.0.1][1]
and the answer helped me.

  [1]: https://android.stackexchange.com/questions/109844/set-open-dns-in-android-5-0-1?newreg=08ac8fdfbb7341fea7e27f4f64642016

Although I just want to change the DNS for blocking porn, what values for the following fields should I enter?

- IP Address
- Gateway
- Network Prefix Length

I have HTC mobile with 5.1 Android version.