What Are Glue Records?

Table of Contents

• The circular dependency problem
• How the parent zone publishes glue
• NS records, A/AAAA records, and glue
• Glue records at DNSimple
• Have more questions?

Glue records are the IP addresses, stored as A or AAAA records, for authoritative name servers when those name server hostnames live inside the domain being delegated. For example, if example.com uses ns1.example.com as one of its name servers, the parent zone, often the TLD, must publish the IP address for ns1.example.com together with the NS delegation.

Resolvers need those IP addresses so they can reach the authoritative name servers before querying the child zone. This prevents the lookup from circling back on itself. For general context on authoritative servers, see What is a name server?.

The circular dependency problem

Imagine example.com is delegated to ns1.example.com and ns2.example.com. That pattern is common with vanity name servers). To talk to ns1.example.com, the resolver needs its IP address. The obvious next step is to look up data for example.com and follow delegation. But delegation already says that example.com is answered by ns1.example.com. You cannot resolve ns1.example.com by asking example.com first without going in a circle.
Glue fixes that. The parent zone (above example.com) publishes the IP addresses for ns1.example.com and ns2.example.com together with the NS records. The resolver gets the IPs from the parent and moves forward without asking the child zone first.

How the parent zone publishes glue

Authoritative data for your zone lives on your name servers, but glue is not ordinary zone content served from the child. It is extra address data the parent returns with delegation. In practice you submit the server names and their addresses to your registrar; the registry stores them so the parent (often the TLD) can answer with both NS and glue for those in-bailiwick names.

Wording matters: some registrars label screens “glue” or “host records,” but the authoritative copy consumers rely on is coordinated through the registration system for your TLD, not a private setting visible only to one ISP.

Typical resolution outline:

1. A resolver needs an answer for www.yourdomain.com.
2. It follows referrals from the root to the TLD for yourdomain.com.
3. The TLD responds with NS records for yourdomain.com pointing at ns1.yourdomain.com and related hosts.
4. If those names are under yourdomain.com, the TLD response also includes glue (A/AAAA) for those hosts so the resolver can open TCP/UDP to them immediately.
5. The resolver queries those authoritative servers for www.yourdomain.com.

Without glue for in-zone server names, many resolvers cannot complete the chain.

NS records, A/AAAA records, and glue

NS records at the parent state which hosts are authoritative for the child zone. When those hosts are out-of-zone (for example ns1.dnsimple.com for example.com), the resolver can resolve ns1.dnsimple.com without glue from the example.com parent. When they are in-zone, glue at the parent carries the bootstrap addresses.

The addresses in glue match what you would express as A or AAAA for those hosts, but they are served from the delegation context at the parent, not retrieved only from the child zone.

Glue records at DNSimple

If DNSimple is your registrar for the domain that owns the vanity hostnames, glue is coordinated through DNSimple when you set up vanity name servers. If registration lives elsewhere, you enter matching glue at that registrar so the registry still receives the correct addresses.

Operational steps are covered in Manage Vanity Name Servers. IP addresses for DNSimple appear in DNSimple Name Servers.

Have more questions?

If you have additional questions about glue records or vanity name servers, contact support, and we will be happy to help.