Editing IPv6 (section)

===Dual-stack IP implementation===
Dual-stack IP implementations provide complete IPv4 and IPv6 protocol stacks in the operating system of a [[computer]] or [[network device]] on top of the common [[physical layer]] implementation, such as [[Ethernet]]. This permits dual-stack hosts to participate in IPv6 and IPv4 networks simultaneously.{{Ref RFC|4213}}

A device with dual-stack implementation in the operating system has an IPv4 and IPv6 address, and can communicate with other nodes in the LAN or the Internet using either IPv4 or IPv6. The DNS protocol is used by both IP protocols to resolve fully qualified domain names and IP addresses, but dual stack requires that the resolving DNS server can resolve both types of addresses. Such a dual-stack DNS server holds IPv4 addresses in the A records and IPv6 addresses in the AAAA records. Depending on the destination that is to be resolved, a DNS name server may return an IPv4 or IPv6 IP address, or both. A default address selection mechanism, or preferred protocol, needs to be configured either on hosts or the DNS server. The [[IETF]] has published [[Happy Eyeballs]] to assist dual-stack applications, so that they can connect using both IPv4 and IPv6, but prefer an IPv6 connection if it is available. However, dual-stack also needs to be implemented on all routers between the host and the service for which the DNS server has returned an IPv6 address. Dual-stack clients should be configured to prefer IPv6 only if the network is able to forward IPv6 packets using the IPv6 versions of [[routing protocols]]. When dual-stack network protocols are in place the [[application layer]] can be migrated to IPv6.<ref>{{Cite book|title=IPv6 Essentials: Integrating IPv6 into Your IPv4 Network|author=Silvia Hagen|publisher=O'Reilly Media, Inc.|year=2014|isbn=9781449335267|pages=222}}</ref>

While dual-stack is supported by major [[operating system]] and network device vendors, legacy networking hardware and servers do not support IPv6.