“Glue records” are DNS entries in the top level domain name that allows for a domain to look at itself to resolve IP-addresses. In my case, using Lan2k.org as DNS, and wanting to host this myself, I needed to notify my registrar to add glue records into the “.org” -domain.

Run: host -t NS lan2k.org will say:
lan2k.org name server ns1.lan2k.org.
lan2k.org name server ns2.lan2k.org.

Do get this working, my registrar has added these entries as glue records into the .org-domain:
ns1.lan2k.org. 86400 IN AAAA 2a01:4f8:200:91f3::6
ns2.lan2k.org. 86400 IN AAAA 2a01:4f8:200:91f4::6
ns1.lan2k.org. 86400 IN A 144.76.218.244
ns2.lan2k.org. 86400 IN A 144.76.218.245

To read these records from .org, run this command to find which servers are hosting .org:
dig +short org. NS

Then ask one of those servers what records it has for lan2k.org:
dig +norec @b0.org.afilias-nst.org. lan2k.org. NS

This means I must have valid servers running on the IP’s listed above. If those server change IP, you need to notify the registrar so that they can update the glue.