Dualstack

Dual-stack refers to a networking configuration in which devices, networks, or links run both IPv4 and IPv6 protocol stacks simultaneously. This approach is commonly used during the transition from IPv4 to IPv6, enabling continued access to IPv4-only services while gradually deploying IPv6 for new or migrated services.

In a dual-stack environment, each host maintains a IPv4 address and an IPv6 address. DNS resolution can return both A (IPv4) and AAAA (IPv6) records for a domain, allowing clients to attempt connections over either protocol. Connection establishment may use the IPv6 path first, or employ mechanisms like the Happy Eyeballs algorithm to try both families and select the fastest working option. Routers on the network carry traffic for both protocols. While IPv4 traffic often traverses NAT (Network Address Translation), IPv6 is usually deployed without NAT, though translation mechanisms such as NAT64/NAT46 may be used in mixed environments.

Deployment considerations include coherent addressing plans, firewall and security rule coverage for both stacks, and comprehensive monitoring of dual-stack traffic. Although dual-stack reduces reliance on translation gateways, it increases management complexity and can broaden the attack surface if security controls are not consistently applied across both protocols. The continued depletion of IPv4 addresses is a motivation for IPv6 adoption, but dual-stack implementations must contend with coexistence challenges and potential performance trade-offs.

Standards and adoption: dual-stack is widely supported across modern operating systems and network equipment. The Happy Eyeballs approach for faster IPv4/IPv6 connection setup is described in RFC 8305, while IPv6 transition mechanisms and related guidance are covered in RFCs such as 4213 and related documents.