What is a Glue Record?
A Glue Record is an A or AAAA record stored in the parent DNS zone that provides the IP address of a nameserver when that nameserver's hostname is within the domain it serves, preventing a circular dependency in DNS resolution.
The Circular Dependency Problem
Without Glue Records (Circular Dependency):
Query: "What is the IP of www.example.com?"
↓
Resolver asks: "Who are the nameservers for example.com?"
↓
Answer: ns1.example.com
↓
Resolver asks: "What is the IP of ns1.example.com?"
↓
Needs to query example.com nameservers...
↓
But we don't know their IP! (Loop)
How Glue Records Solve This
With Glue Records at .com TLD:
.com Zone File:
example.com. NS ns1.example.com.
example.com. NS ns2.example.com.
ns1.example.com. A 192.0.2.1 ← Glue Record
ns2.example.com. A 192.0.2.2 ← Glue Record
Resolution Flow:
Query for www.example.com
↓
.com servers return NS records + Glue IPs
↓
Resolver can now contact 192.0.2.1 directly
↓
Resolution completes successfully
When Glue Records Are Required
| Nameserver Location | Glue Required | Example |
|---|---|---|
| Within same domain | Yes | ns1.example.com for example.com |
| Different domain | No | ns1.hostingco.com for example.com |
| Subdomain of target | Yes | ns1.dns.example.com for example.com |
Glue Record Types
| Record Type | Purpose | Example |
|---|---|---|
| A | IPv4 address for nameserver | ns1.example.com A 192.0.2.1 |
| AAAA | IPv6 address for nameserver | ns1.example.com AAAA 2001:db8::1 |
Common Configuration Scenarios
Scenario 1: Self-hosted nameservers
Domain: example.com
Nameservers: ns1.example.com, ns2.example.com
→ Glue records REQUIRED at registrar
Scenario 2: Third-party nameservers
Domain: example.com
Nameservers: dns1.provider.com, dns2.provider.com
→ No glue records needed
Scenario 3: Vanity nameservers pointing elsewhere
Domain: example.com
Nameservers: ns1.example.com → CNAME dns1.provider.com
→ INVALID - NS records cannot point to CNAMEs
→ Must use glue records with actual IPs
Managing Glue Records
Glue records are configured at your domain registrar, not in your DNS zone:
1. Log into registrar control panel
2. Navigate to nameserver/host records section
3. Create host records with nameserver hostname and IP
4. Assign those nameservers to your domain
Best Practices
1. Provide both IPv4 and IPv6: Add A and AAAA glue records
2. Use multiple IPs: Different IPs for ns1 and ns2 for redundancy
3. Keep records updated: Change glue if nameserver IPs change
4. Verify propagation: Check glue with dig +trace
Troubleshooting
# Check glue records for a domain
dig +trace example.com NS
# Verify glue is present in TLD response
dig @a.gtld-servers.net example.com NS +norec
Glue records are essential DNS infrastructure that enables domains to use self-hosted nameservers while maintaining a resolvable DNS hierarchy.