Unexpected RCODE (15)

[Simon Waters]

Has anyone investigated this specific error on recursive servers.

Since 15 is reserved I assume it is from broken name servers of some 
description?

Got a lot more this morning, so I took a brief look. 

I think these are all from lame authoritative servers running BIND (various 
versions), which have recursion enabled.

I note there was a fix to BIND 8 that addresses incorrect RCODE leakage, but 
not all the servers producing this error are running old versions of BIND 
(AFAICT), but if they are doing a recursive lookup that might involve other 
misconfigured DNS servers.