Editing Domain Name System (section)

===Circular dependencies and glue records===
Name servers in delegations are identified by name, rather than by IP address. This means that a resolving name server must issue another DNS request to find out the IP address of the server to which it has been referred. If the name given in the delegation is a subdomain of the domain for which the delegation is being provided, there is a [[circular dependency]].

In this case, the name server providing the delegation must also provide one or more IP addresses for the [[authoritative name server]] mentioned in the delegation. This information is called ''glue''.   The delegating name server provides this glue in the form of records in the ''additional section'' of the DNS response, and provides the delegation in the ''authority section'' of the response. A glue record is a combination of the name server and IP address.

For example, if the [[authoritative name server]] for example.org is ns1.example.org, a computer trying to resolve www.example.org first resolves ns1.example.org. As ns1 is contained in example.org, this requires resolving example.org first, which presents a circular dependency. To break the dependency, the name server for the [[top level domain]] org includes glue along with the delegation for example.org.  The glue records are address records that provide IP addresses for ns1.example.org. The resolver uses one or more of these IP addresses to query one of the domain's authoritative servers, which allows it to complete the DNS query.