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Set Up an IPv6-Mostly Network

Twofer

Article from ADMIN 92/2026

By Mathias Hein

IPv6-mostly networks primarily use IPv6 for communication but also support IPv4 as a fallback, simplifying address management, reducing the load on the IPv4 infrastructure, and allowing IPv6-only and IPv4-enabled endpoints to coexist on the same network. We describe transition mechanisms that facilitate the operation of an IPv6-mostly network and the few technical hurdles to overcome.

For years, networks have been slated to migrate to IPv6 to address the shortage of IPv4 addresses. This problem can be an issue for users, because many older devices, applications, and services still in use do not work properly in a IPv6-only environment. Therefore, dual-stack networks currently offer the best user experience, but at the expense of running out of IPv4 addresses. Although most network operators initially tend to introduce IPv6 in parallel with their existing IPv4 infrastructure, IPv6-only networks are still uncommon outside the mobile communications sector. Most admins agree that the dual-stack approach is an unavoidable transition phase that allows lessons to be learned with the IPv6 protocol while minimizing disruptions to network operations.

Admittedly, dual-stack networks do not solve the core problem: running out of IPv4 addresses. A network operator still needs the same IPv4 resources as for an IPv4-only network. Worse still, a dual-stack infrastructure often has to remain in operation for many years. Many applications still rely on IPv4, as well, which leads to a chicken-and-egg problem: IPv6-only networks are impractical for incompatible applications, while applications continue to rely on IPv4 because IPv6-only networks are rare.

One possible solution is what are dubbed IPv6-mostly networks, which provide IPv4 connectivity when needed and allows IPv6-enabled devices to operate in IPv6-only mode, while IPv4 is seamlessly delivered to those who need this protocol version.

What Defines IPv6-Only Networks?

An IPv6 network is very similar to a dual-stack network, with two additional key elements. First, the network provides NAT64 functionality in line with RFC 6146 [1], which enables IPv6-only clients to communicate with IPv4 destinations. Second, the DHCPv4 infrastructure processes the DHCP IPv6-Only

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