Edvina AB Cisco Systems Ariadne The Session Initiation Protocol (SIP) supports multiple transports running both over IPv4 and IPv6 protocols. In more and more cases, a SIP user agent (UA) is connected to multiple network interfaces. In these cases setting up a connection from a dual stack client to a dual stack server may suffer from the issues described in RFC 6555 [RFC6555] ("Happy Eyeballs") - significant delays in the process of setting up a working flow to a server. This negatively affects user experience. This document builds on RFC 6555 and explains how a [RFC3261] compliant SIP implementation can minimize delays when contacting a host name (obtained by using DNS NAPTR and SRV lookups) in a dual stack network using connection-oriented transport protocols.