Re: [DNSOP] terminology: glue

Glue records are necessary to prevent circular references, i.e. to cut the loop.  The most obvious and common situation is where the name server is below the cut.  If the address of the name server were not included, the querying system would keep being referred to the parent, i.e. stuck in a loop of length 1.  It is also possible to have loops of length 2 or more, though these will be quite rare.  If the name servers for A are below B, and the name servers for B are below A, if glue records are not included for either, the querier will bounce back and forth between A and B without ever succeeding.

It would be nice if the definition of glue records included the complete picture, though that might make it harder for people to understand the basic case.  So, a brief bit of explanatory and example text in addition to the formal definition would also be advisable.

Steve

On May 4, 2015, at 10:32 AM, Casey Deccio <casey@deccio.net> wrote:

> I am still a bit uncomfortable with the -01 definition of glue, specifically the reference to RFC 2181.  I think the reference to RFC 2181 is useful and necessary, but I hesitate to think that RFC 2181's use of glue is a redefinition that is intended to apply outside of the RFC itself.  That is, I believe the term was overloaded (similar to the apparent overloading of "label" discussed in another recent dnsop thread).
> 
> Here is some proposed re-wording (modified from a previous proposal), which both adds more context (quoted from earlier RFC 1034 text) for the use of glue to the first paragraph and gives less weight to the RFC 2181 reference in the second.
> 
> Glue records -- "[Records] which are not part of the
>    authoritative data [for a zone], and are address resource records for
>    the servers [in a subzone].  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." (Definition from RFC 1034, 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" ([RFC2181], section 5.4.1).  Although glue is sometimes used
>    today with this wider definition in mind, the context surrounding the
>    RFC 2181 definition suggests it is intended to apply to the use of glue
>    within document itself and not necessarily beyond.
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