Appendix A. Differences from RFC 6555

"Happy Eyeballs: Success with Dual-Stack Hosts" [RFC6555] mostly concentrates on how to stagger connections to a hostname that has a AAAA and an A record. This document additionally discusses:

• how to perform DNS queries to obtain these addresses

• how to handle multiple addresses from each address family

• how to handle DNS updates while connections are being raced

• how to leverage historical information

• how to support IPv6-only networks with NAT64 and DNS64

Note that a simple implementation of the algorithm described in this document is still compliant with the previous specification [RFC6555]. Implementations should take the new considerations into account when applicable to optimize their behavior.