DNS Long-Lived Queries
DNS Long-Lived Queriesis a mechanism that allowsDNSclients to learn about changes to DNS data withoutpolling.[1]
DNS LLQ is currently used byApple Inc.'sBack To My Mac(BTMM) service to track changes in the IP addresses of BTMM servers and clients.[2] DNS LLQ has also been proposed as a solution for doingDNS-Based Service Discovery(DNS-SD) on routed networks, using long-livedTCP/IPconnections. DNS-SD is a mechanism for identifying services on the local network.[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 theIETFDNSSD working group as one option for providing service discovery in these routed networks.[4]Although DNS LLQ over TCP/IP has not been standardized, it is in use in Apple Inc.'s currentmDNSimplementation.[5]
DNS LLQ is initiated by a clientresolverthat wishes to track one or more names in the DNS. The client resolver sends a registration message to acaching server,or to theauthoritative serverfor the zone containing the name or names to be tracked. The query includes a lease; the tracking persists for the duration of the lease. If tracking is desired after the lease expires, the client resolver sends a new registration. The registration message includes a list of one or more queries. The server immediately returns the answers it has for these queries. 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. Before the queries are answered and the lease recorded, the server and client perform a challenge/response exchange to validate the registration. Gratuitous answers are acknowledged by the client, and retransmitted if not acknowledged. After several tries, the server holding the registration will assume that the client resolver is no longer available, and will delete the registration.[1]
References
[edit]- ^abCheshire, Stuart."DNS Long-Lived Queries".IETF.Retrieved3 March2014.
- ^Cheshire, Stuart (June 2011)."Understanding Apple's Back to My Mac (BTMM) Service".IETF.Retrieved4 March2014.
- ^Cheshire, Stuart (2006)."DNS-Based Service Discovery".IETF.Retrieved3 March2014.
- ^Bhandari, Schweta (21 October 2013)."Extending Multicast DNS across Local Links in Campus and Enterprise Networks".IETF.
- ^"Private DNS".Apple Inc.Retrieved4 March2014.
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