I can't think of a recursing resolver which discards / disallows non-hostname queries. The only case I've run into, ever, is the stub resolver in the Ignition S

I can't think of a recursing resolver which discards / disallows non-hostname queries. The only case I've run into, ever, is the stub resolver in the Ignition SCADA platform (running Java on top of the Azul JVM). (It's on my list to try loading the Python 2 version of dnspython and see if that works. Yeah, Ignition's internal scripting layer is running Jython, at version 2.) Edit: that's not to say that some middlebox isn't dropping them in the name of "securitah".