@Walter Hinteler,
From my hearing it is all so call porn sites not just child porn and any such child porn sites would not need to be block as under international agreements and the US that in fact control such things as IP addresses they would be pull down and the people running them arrested in almost any country in the world.
In public libraries in the US must have filters if they take money from the federal government however those filters are normally disable at adults users requests.
Child porn and to a lesser degree porn is an excuse used by governments to censor the net and in almost every case that filtering is found to go way beyond porn sites with many others sites that have nothing to do with porn ending up on block lists.
Footnote the Miami Dade public library filtering cover a great deal more then porn sites such as the torproject.org site until I and other complain. Not that it matter to me except on principle as I always have the tools on my computers to get around such filtering.