Update forwarding is a DNS concept in some name server implementations
that enables dynamic updates to be sent to a name server that is not
the primary master name server for the zone being updated. The name
server that receives the dynamic update request forwards the update
to the primary master name server.
Rule: To avoid possible zone data-integrity
issues, ADNR must be configured to update only the primary master
name server for a zone. That is, the IP address of a name server on
the dns_id keyword of the dns statement must be an address of the
primary master name server for the zone identified on the domain_suffix
keyword, and must not be the IP address of a secondary name server
for that zone.