FaceTime error check network connection and try again

When I sign into FaceTime on my iPad 2, the FaceTime login failed and I get the error "check network connection and try again". But I can surf the web and the WiFi network works fine.To fix the FaceTime issue, tap setting > WiFi > network and add 8.8.8.8, 8.8.4.4 to the DNS settings. The problem fixed.