In normal DNS resolution, when a resolver attempts to reach a domain name, it first queries the root, which provides the top-level domain, then queries the top-level domain servers, which provide the authoritative name servers for the domain, and finally, it queries the authoritative name servers for the domain to resolve the domain name. If a domain’s name servers exist within the domain itself, a glue record is needed to resolve the domain name.
What is a Glue Record?
Glue records are DNS records created at the domain registrar. The record provides a complete answer when the TLD name server returns a referral to an authoritative name server for a domain. For example, the domain name “example.com” has nameservers “ns1.example.com” and “ns2.example.com”. To resolve the domain name, the DNS would query in order: root, TLD name server, and authoritative name server. However, by having the authoritative name servers within the domain itself, these name servers cannot be found without external assistance. This is called a “circular referral”. The creation of a glue record, an A record served by the TLD name server, prevents circular referrals and allows for both DNS name resolution and the listing of name servers within the domain itself.
When do I need a Glue Record?
You need to create a glue record when you host your own authoritative servers. If a third party, such as a managed DNS provider, hosts your authoritative nameservers, then the provider is responsible for setting up the glue record.
When you host your own licensed servers, you need to set up glue records with your domain registrar to keep everything working properly.