DNS/RFC/8499/referralsについて、ここに記述してください。


Referrals:
  A type of response in which a server, signaling that it
      is not (completely) authoritative for an answer, provides the
      querying resolver with an alternative place to send its query.
      Referrals can be partial.



Delegation:
  The process by which a separate zone is created in the
      name space beneath the apex of a given domain.  Delegation happens
      when an NS RRset is added in the parent zone for the child origin.
      Delegation inherently happens at a zone cut.  The term is also
      commonly a noun: the new zone that is created by the act of
      delegating.

Lame delegation:  "A lame delegations exists [sic] when a nameserver
      is delegated responsibility for providing nameservice for a zone
      (via NS records) but is not performing nameservice for that zone
      (usually because it is not set up as a primary or secondary for
      the zone)."  (Quoted from [RFC1912], Section 2.8) Another
      definition is that a lame delegation "...happens when a name
      server is listed in the NS records for some domain and in fact it
      is not a server for that domain.  Queries are thus sent to the
      wrong servers, who don't know nothing [sic] (at least not as
      expected) about the queried domain.  Furthermore, sometimes these
      hosts (if they exist!) don't even run name servers."  (Quoted from
      [RFC1713], Section 2.3)

Glue records:  "...[Resource records] which are not part of the
      authoritative data [of the zone], and are address RRs for the
      [name] servers [in subzones].  These RRs are only necessary if the
      name server's name is 'below' the cut, and are only used as part
      of a referral response."  Without glue "we could be faced with the
      situation where the NS RRs tell us that in order to learn a name
      server's address, we should contact the server using the address
      we wish to learn."  (Quoted from [RFC1034], Section 4.2.1)

      A later definition is that glue "includes any record in a zone
      file that is not properly part of that zone, including nameserver
      records of delegated sub-zones (NS records), address records that
      accompany those NS records (A, AAAA, etc), and any other stray
      data that might appear."  (Quoted from [RFC2181], Section 5.4.1)

Although glue is sometimes used today with this wider definition
      in mind, the context surrounding the definition in [RFC2181]
      suggests it is intended to apply to the use of glue within the
      document itself and not necessarily beyond.