[dns-operations] NS records in Authority for NOERROR responses

[Mark Andrews]

Returning NS records also helps when the parent servers also serve
the child zone and the two sets of servers differ.  Without NS
records being returned you would never ask any server but the parent
servers.

This sort of this is common in large organisation.  The parent zone
servers are slaves for all the child zones.  This optimises for the
initial lookup by reducing one rtt but doesn't spread the load of
subsequent lookups to all the servers for the child zone unless the
NS records are also returned.

Mark
-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka at isc.org