DNS/用語/glue/survey/glue-policyについて、ここに記述してください。

This is a list of existing glue policies:

"never" or "null":  Glue RRs are never registered. 
   This currently applies to larger parts of the IN-ADDR.ARPA reverse tree.
      XXX but this interacts with the naming schemes to be applied.

"narrow":  Glue RRs are registered if and only if the name server resides within or below the delegated (child) zone
    (that is, within the delegated domain).  This was suggested by [RFC1034].

"wide":  Glue RRs are registered if and only if the name server resides below the delegating (parent) zone. 
   If the name server's name belongs to the parent zone, 
   it is part of the authoritative data and thus there is no need to register glue RRs.
    This was suggested by [RFC1033].  It is used for the root zone.

"case by case":  Glue RRs are registered following the "narrow" policy except where there are (circular) dependencies that demand
      additional glue RRs.

"mandatory":  Glue RRs are always registered for all name servers.  This was suggested by [RFC0973].

"other":  Combinations of the above may exist,
   e.g. if a registry runs multiple sibling domains and decides to register glue RRs
      whenever a name server resides in or below one of the siblings.
      This category would also include other policies like "random" or "arbitrary".

Glue RRs are needed only in the delegating zone, regardless of glue policy. 
See Section 5.1 for a discussion of root zone issues.

Various RFCs have identified extraneous glue RRs as sources of error and confusion ([RFC1713], [RFC1912]).