ZDNS This document defines the _str._dns-sd._udp (Service Type Routing) metadata label, a backward-compatible extension for SRP registration. This mechanism relaxes the original single-registration-domain constraint, enabling clients to publish distinct service types to independent target DNS zones and dedicated SRP registrar instances. It supports fine-grained operational tuning, administrative isolation of heterogeneous services. This extension only modifies SRP registration domain selection logic, fully preserves existing SRP wire format, authentication, leasing and discovery behaviors, and introduces no impact on DNS-SD service browsing operations.