... which can result from the wrong server being asked to fulfill a request due to DNS issues. I've seen blocking implemented by responding with another server

... which can result from the wrong server being asked to fulfill a request due to DNS issues. I've seen blocking implemented by responding with another server address that is supposed to give some meaningful responses (an "ad blocked" image instead of the user just getting an unable-to-load image icon, for instance). This is getting less useful as HTTPS becomes more ubiquitous as you need to install your own signing key on the client machines to pull it off and it isn't often with the hassle, but it is still sometimes attempted. I've also seen DNS level blocking send out 127.0.0.1 which strikes me as stupid.