Nameservers on the domain they serve.
THE PROBLEM THEY SOLVE
If ns1.yourdomain.com is a nameserver for yourdomain.com, finding it requires asking yourdomain.com's nameservers, which is circular.
A glue record breaks the circle by publishing the address at the registry level.
WHEN YOU NEED THEM
Only when running private nameservers on your own domain, typically as a reseller.
Not for ordinary hosting.
HOW TO CREATE THEM
At your registrar, usually under a heading such as register a host, child nameserver, or private nameserver.
Enter the hostname and the address.
WHAT TO ENTER
ns1.yourdomain.com with its address, and ns2.yourdomain.com with its address.
THE COMMON FAILURE
Setting private nameservers in WHM without creating the glue records at the registrar.
The nameservers do not resolve, and nothing works. This is the single most common private nameserver problem.
CHECKING
Look up ns1.yourdomain.com. It must return the correct address.
If it does not resolve, the glue record is missing.
CHANGING THE ADDRESS
Update the glue record at the registrar as well as anywhere else.
