DNS Long-Lived Queries

[2] DNS LLQ has also been proposed as a solution for doing DNS-Based Service Discovery (DNS-SD) on routed networks, using long-lived TCP/IP connections.

[3] DNS-SD is typically used to present names of services (for example, printers or file servers) in user interfaces.

DNS Long-Lived Queries (DNS-LLQ) can be used for DNS-SD to allow new services to appear automatically in an active user interface without requiring frequent polling.

DNS-LLQ is being proposed in the IETF DNSSD working group as one option for providing service discovery in these routed networks.

For the duration of the lease, whenever the information covered by any of the queries changes, the server sends a "gratuitous response" containing new answers.