A delegation points to nameservers
DNS delegation tells resolvers which nameservers to ask about a domain. For example, the parent zone for example.com can list ns1.example.com and ns2.example.com as nameservers for that domain. A resolver needs the IP address of at least one of those nameservers before it can send a query there.
An NS record supplies a nameserver’s hostname, not its IP address. Usually, the resolver can look up that hostname through DNS. But when the hostname is inside the very domain being delegated, that ordinary lookup runs into a problem: the resolver must reach the domain’s nameserver to learn the nameserver’s address. Glue records provide a way past this circular dependency.
How glue breaks the circular lookup
Suppose example.com is delegated to ns1.example.com. A resolver asks the .com nameservers where to find example.com and receives a referral naming ns1.example.com. Without an address for ns1.example.com, the resolver cannot contact it. Asking DNS for that address leads back to the delegation it has not yet been able to follow.
The parent can include a glue A record, an AAAA record, or both alongside the referral. These records give the resolver an address it can use to contact ns1.example.com. Once it reaches the nameserver, the resolver can ask for the requested information in example.com. Glue is therefore a practical starting point, not a replacement for the domain’s own DNS records.
Glue is most clearly needed when a nameserver’s hostname is within the domain it serves, often called an in-bailiwick nameserver. If example.com instead uses ns1.example.net, the resolver can normally find that address by following the separate DNS path for example.net. In that case, the example.com delegation does not need glue for ns1.example.net.
Glue is not the same as an authoritative address record
Glue is address information supplied with a referral by the parent side of a delegation. The authoritative DNS zone for example.com can also contain A or AAAA records for ns1.example.com. Those records serve a different role: they are the domain’s own answers about that hostname. Keeping the glue and authoritative address records consistent helps resolvers reach the intended server reliably.
The parent’s delegation NS records and the child zone’s NS records should also describe the intended nameservers consistently. A mismatch can make a setup harder to understand and troubleshoot, even if some queries still succeed. Likewise, if a nameserver moves to a new IP address, changing only its A or AAAA record in the child zone may leave the parent’s glue pointing at the old address.
Glue is not needed simply because a domain has nameservers. It is needed when the referral cannot be followed without an address supplied at that point in the lookup. The registrar or DNS provider may call the setup step “registering a nameserver,” “host records,” or something similar; the exact interface varies.
What to check when setting up a delegation
Start with the nameserver hostnames you intend to use. If they are inside the domain being delegated, check that their IP addresses are registered where the parent delegation is managed. Add A glue for an IPv4 address and AAAA glue for an IPv6 address only when the corresponding nameserver service is available at that address. Then confirm that the nameservers answer authoritatively for the domain and that their own address records match the glue.
If a delegation fails, check the pieces separately: which NS names the parent returns, whether the referral includes usable glue where needed, whether those addresses reach a DNS server, and whether that server answers for the domain. This sequence helps distinguish a missing-glue problem from a server outage or an incorrect zone configuration.
Glue records solve a narrow but important problem. They give a resolver enough information to take the first step toward a nameserver whose address would otherwise be locked behind the same delegation.
