I think that jitspoe's heatbeat script should query the servers to see if they get anything before foolishly adding another ip/port to the list. These days there's usually 30 garbage servers on the list from people who cannot setup their router properly.
Problem is, when the server sends a heartbeat to the server on whatever particular random port it may be, that port will be open for responses, so if I query it, chances are, it will all work OK. I've considered restricting allowed port ranges to like 279XX, but some existing servers run on crazy port numbers.