Is there a legitimate reason why an NTP time server returns 0xFFFFFFFF on response to a request for a time stamp? I can think of a couple of reasons one being a clash of simultaneous requests on a server of limited ability like a router. The other it may just be a bloody minded response by the server to being asked too often by the same client.
Any other thoughts elsewhere or is it something else to trap in the code before using the answer.
"The other it may just be a bloody minded response by the server to being asked too often by the same client."
You should be able to sort that one out yourself.
Is there a legitimate reason why an NTP time server returns 0xFFFFFFFF on response to a request for a time stamp?
An NTP server doesn't return just one 32bit integer value. By looking at the rest of the packet you might find the reason for the rather unusual value. Post the content of the complete UDP packet so we might be able to tell you more.