Apple Inc Apple Inc DNS Service Discovery provides several mechanisms whereby hosts can discover and advertise services on an IP network. Such discovery can be done using Multicast DNS (mDNS) or DNS, and advertising can be done with DNS-SD Service Registration Protocol (SRP) or mDNS. This document defines Unicast Local Discovery (ULD), a service that combines an SRP registrar, a Discovery Proxy, and an Advertising Proxy. Hosts can use a ULD server to advertise and discover services on the local link entirely via unicast SRP and DNS while remaining interoperable with hosts that use mDNS.