* AXFR/UDP query is responded as FORMERR (according to BIND and RFC1034)
* IXFR/UDP query is responded with SOA (according to RFC1995)
* Experimental support for (A|I)XFR/UDP is implemented, but disabled.
** I did not encounter server supporting full IXFR/UDP nor client tool to test it.
** AXFR/UDP is still in state of draft and not supported, so disabled as well.

refs #984