Glue Record

A Glue Record is a type of DNS record that associates a nameserver’s hostname with its IP address, helping to resolve potential circular dependencies.

More About Glue Records

Glue records are used in situations where a domain’s authoritative DNS server is within the same domain it serves. Here’s more information about glue records:

1. DNS Hierarchy and Delegation: DNS operates in a hierarchical structure. At the top of the hierarchy are the root servers, which store information about the top-level domains (TLDs) like .com, .org, .net, and country-code TLDs (ccTLDs) such as .uk, .ca, and .de. Below the TLDs are second-level domains (SLDs), and beneath those are subdomains.
2. Delegation of Subdomains: When a domain is delegated to a different set of DNS servers, it requires glue records. This commonly occurs when a domain registrar or hosting provider manages the authoritative DNS servers for a domain on behalf of the domain owner. For example, if you own the domain example.com and use a hosting provider’s DNS servers, the DNS records for example.com are managed by the hosting provider’s authoritative DNS servers.
3. Glue Records Definition: Glue records are DNS records that provide the IP addresses of the authoritative DNS servers responsible for a specific subdomain. These records are necessary because, in some cases, the DNS resolver needs to know the IP addresses of the authoritative servers before it can resolve the domain name itself. This creates a bit of a “chicken and egg” problem, which glue records solve.
4. Use Cases for Glue Records: Glue records are primarily used in the following scenarios:
   • Name Server Delegation: When a domain is delegated to custom name servers (e.g., ns1.example.com and ns2.example.com), glue records are required to associate the IP addresses of those name servers with the domain’s authoritative DNS servers.
   • Subdomain Delegation: In cases where a subdomain is delegated to different name servers (e.g., sub.example.com delegated to ns1.sub.example.com), glue records provide the IP addresses of ns1.sub.example.com.
5. Glue Records in DNS Zone Files: Glue records are typically configured in the DNS zone file of the parent domain (e.g., example.com) rather than the subdomain (e.g., sub.example.com) because the parent domain’s authoritative DNS servers are responsible for providing the IP addresses. These records consist of A (IPv4 address) or AAAA (IPv6 address) resource records.
6. DNS Resolver Usage: When a DNS resolver encounters a domain name that requires glue records, it uses the information from the glue records to find the IP addresses of the authoritative name servers. Once it has this information, it can proceed with DNS resolution for the domain, including resolving any subdomains under it.
7. Glue Record Maintenance: Glue records need to be kept up to date when the IP addresses of authoritative DNS servers change. Domain registrars typically provide tools for managing glue records when custom name servers are used.

In summary, glue records are DNS records that provide the IP addresses of authoritative DNS servers responsible for subdomains or delegated domains. They are crucial for DNS resolution in cases where the authoritative servers’ domain is within the same domain they serve.