Glue records: when your nameservers need them
Glue is an address (A/AAAA) record that the parent zone includes alongside a delegation, so a resolver can reach your nameserver without a chicken-and-egg lookup.
When glue is needed
Glue is required when a nameserver's hostname is inside the domain it serves: for example if example.com is served by ns1.example.com. To look up example.com you need ns1.example.com, but that name is itself in example.com - so the parent must supply ns1.example.com's address as glue. Nameservers that live in a different domain (like ns1.some-dns-host.net) usually do not need glue.
What the report checks
- Whether the parent sent glue where it is needed.
- Whether the glue addresses match the addresses your own nameservers publish (stale glue points resolvers at an old IP).
How to fix it
Glue is managed at your registrar as part of registering a "host" or "child nameserver" record. If you renumber a nameserver that lives inside your own domain, update the glue at the registrar as well as the A/AAAA record in your zone, and keep them equal.
How to verify
dig example.com NS +norecurse @a.gtld-servers.net
Look at the ADDITIONAL section: the glue addresses shown there should match dig ns1.example.com A +short.