Original text:
2.  The following is a simple example of glue records present in the delegating zone "test" for the child zone "foo.test".  The nameservers for foo.test (ns1.foo.test and ns2.foo.test) are both below the delegation point.  They are configured as glue records in the "test" zone: <del> Referral responses from "test" for "foo.test" must include the glue records in the additional section (and set TC=1 if they do not fit): </del>  <del> 2.1. </del>  While not common, real life examples of servers that fail to set TC=1 when glue records are available, exist and they do cause resolution 3.  Replace "Copy the NS RRs for the subzone into the authority section of the Referral responses from "test" for "foo.test" must include the sibling glue (and set TC=1 if they do not fit):  This document clarifies correct DNS server behaviour and does not introduce any changes or new security considerations. <del> 5. </del>  There are no actions for IANA. <del> 6. </del>  The authors wish to thank Joe Abley, Brian Dickson, Geoff Huston, Jared Mauch, George Michaelson, Benno Overeinder, John R Levine,

Reviewer comments:
work in progress. please do not merge without review & discussion.
Should we use the naming for Glue from 8499?
"Sibling domain glue" "in-domain glue" and maybe we should define "orphan glue/promoted glue". while we have 8499bis open?
IMO 8499 doesn't have glue definitions that are useful for this draft, so yeah, maybe they should be added to 8499.

Revised text:
2. <ins> This section describes different types of glue that may be found in DNS referral responses.  Note that the type of glue depends on the QNAME.  A particular record can be in-domain glue for one response and sibling glue for another. 2.1. </ins> The following is a simple example of glue records present in the delegating zone "test" for the child zone "foo.test".  The nameservers for foo.test (ns1.foo.test and ns2.foo.test) are both below the delegation point.  They are configured as glue records in the "test" zone:  <ins> A referral response from "test" for "foo.test" with in-domain glue looks like this: </ins>  <ins> 2.2. Sibling glue are glue records that are not contained in the delegated zone itself, but in another delegated zone from the same parent.  In many cases, these are not strictly required for resolution, since the resolver can make follow-on queries to the same zone to resolve the nameserver addresses after following the referral to the sibling zone.  However, most nameserver implementations today provide them as an optimization to obviate the need for extra traffic from iterative resolvers. Here the delegating zone "test" contains 2 sub-delegations for the subzones "bar.test" and "foo.test": A referral response from "test" for "foo.test" with sibling glue looks like this: 2.3. [missing glue isn't really a type of glue, so we'll need to think about this] </ins> While not common, real life examples of servers that fail to set TC=1 when glue records are available, exist and they do cause resolution 3. <ins> 3.1. This document clarifies that when a name server generates a referral response, it MUST either include all in-domain glue records in the additional section, or MUST set TC=1. 3.2. This document clarifies that when a name server generates a referral response, it SHOULD include available sibling glue records in the additional section.  If sibling glue records do not fit in the response, the name server is NOT REQUIRED to set TC=1. 3.3. Promoted glue is a special case of sibling glue and should be treated as such. 3.4. [this doesn't really account for SHOULD on sibling glue...] </ins> Replace "Copy the NS RRs for the subzone into the authority section of the Referral responses from "test" for "foo.test" must include the sibling glue (and set TC=1 if they do not fit): <ins> 5. </ins> This document clarifies correct DNS server behaviour and does not introduce any changes or new security considerations.  <ins> 6. </ins> There are no actions for IANA.  <ins> 7. </ins> The authors wish to thank Joe Abley, Brian Dickson, Geoff Huston, Jared Mauch, George Michaelson, Benno Overeinder, John R Levine,