"RFC 3263 defines how a Session Initiation Protocol (SIP) implementation@ given a SIP Uniform Resource Identifier (URI)@ should locate the next-hop SIP server using Domain Name System (DNS) procedures. As SIP networks increasingly transition from IPv4-only to dual-stack@ a quality user experience must be ensured for dualstack SIP implementations. This document updates the DNS procedures described in RFC 3263 for dual-stack SIP implementations in preparation for forthcoming specifications for applying ""Happy Eyeballs"" principles to SIP."