Error 451, 404 Error Simulated

Anyone who from under “Rostelecom” or another obviously Russian provider had to go to http://drugoi.livejournal.com/3712998.html (blacklisted for portraying political suicide), of course, he saw a goat the inscription "error 451!":



However, you can use any HTTP response header viewer and see that there is actually a 404 error (“Not Found”).
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Similarly, the situation in the Node.js engine: code 451 will not add to the list of predefined HTTP response codes until the corresponding Google proposal becomes the standard.