Description Markus Kuppe 2010-08-06 05:16:55 EDT

"Internet Draft            DNS Long-Lived Queries        10th August 2006
1. Introduction

   In dynamic environments, DNS Service Discovery [DNS-SD] benefits
   significantly from clients being able to learn about changes to
   DNS information via a mechanism that is both more timely and more
   efficient than simple polling. Such a mechanism enables "live
   browses" that learn when a new instance of a service appears, or when
   an existing service disappears from the network, and allows clients
   to monitor changes to a service. Multicast DNS [mDNS] supports this
   natively. When a host on the network publishes or deletes DNS
   records, these records are multicast to other hosts on the network.
   These hosts deliver the records to interested clients (applications
   running on the host). Hosts also send occasional queries to the
   network in case gratuitous announcements are not received due to
   packet loss, and to detect records lost due to their publishers
   crashing or having become disconnected from the network.

   There is currently no equivalent in traditional unicast DNS. Queries
   are "one-shot" -- a name server will answer a query once, returning
   the results available at that instant in time. Changes could be
   inferred via polling of the name server. This solution is not
   scalable, however, as a low polling rate could leave the client with
   stale information, and a high polling rate would have an adverse
   impact on the network and server.

   Therefore, an extension to DNS is required that enables a client to
   issue long-lived queries. This extension would allow a DNS server to
   notify clients about changes to DNS data.
"

Obviously such a feature is favorable to polling. However, until such a feature exists in DNS, it won't be possible to use it in this provider. Might have to fall back to polling with all its consequences if IDiscoveryLocator listener as well as getAsync* is to be implemented.

[0] http://files.dns-sd.org/draft-sekar-dns-llq.txt