A "glue record" is a type of DNS record used to resolve domain names when the name server for a domain is itself within the domain being queried. Essentially, glue records are necessary to avoid circular dependencies in DNS resolution.
Here's how it works:
- Scenario: Suppose you have a domain example.de, and the authoritative name server for is example.de is ns.example.de.
- Problem: If someone wants to resolve example.de, they need to know the IP address of ns1.example.de. But to find ns1.example.de, they need to resolve example.de first, creating a circular dependency.
- Solution: Glue records provide the IP address of the name server directly in the parent zone (in this case, the .de zone), breaking the circular dependency.
- Implementation: When you register a domain and specify name servers that are subdomains of the domain itself, please provide the IP addresses for those name servers. These IP addresses are then included as glue records in the parent zone. The CNR API handles this using the name server commands available here: https://kb.centralnicreseller.com/api/api-commands/api-command-reference#cat-nameserver
Glue records are crucial for the proper functioning of DNS when the name servers are within the domain they serve.
Please note that TLD-specific requirements may apply.