{"id":33023,"date":"2026-03-17T20:08:19","date_gmt":"2026-03-17T20:08:19","guid":{"rendered":"https:\/\/blog.lacnic.net\/?p=33023"},"modified":"2026-03-19T13:42:44","modified_gmt":"2026-03-19T13:42:44","slug":"ipv6-mostly-frontier","status":"publish","type":"post","link":"https:\/\/blog.lacnic.net\/en\/ipv6-mostly-frontier\/","title":{"rendered":"IPv6-Mostly: The Final Frontier"},"content":{"rendered":"\n

By Henri Alves de Godoy<\/a><\/p>\n\n\n\n

As IPv6 adoption advances, network architectures operating predominantly over IPv6 are beginning to emerge. In this context, mechanisms such as Option 108 (IPv6-Only Preferred)<\/strong> defined in RFC 8925, Pref64<\/strong> discovery in Router Advertisements (RFC 8781), and the 464XLAT<\/strong> model, widely used in mobile networks, have gained greater operational relevance.<\/p>\n\n\n\n

In practice, however, confusion persists between two distinct concepts: IPv6-mostly<\/strong> and IPv6-only<\/strong>. This article discusses this conceptual difference, analyzes the role of these mechanisms, and presents practical implications observed in various operating systems and network environments.<\/p>\n\n\n\n

The Road Towards IPv6-Only Networks<\/strong><\/h2>\n\n\n\n

In the opening sequence of Star Trek<\/em>, space is described as the final frontier<\/strong>, a world that remains to be explored, where new discoveries redefine the limits of knowledge.<\/p>\n\n\n\n

In many ways, the evolution of IP networks is currently going through a similar time. After decades of coexistence between IPv4 and IPv6, the Internet is approaching a new frontier: the moment when IPv6-only<\/strong> architectures cease to be mere experiments or isolated deployments and start to represent a viable operational model across different environments.<\/p>\n\n\n\n

The concept of IPv6-mostly<\/strong> networks emerged in this scenario, introduced by RFC 8925, along with mechanisms such as Option 108<\/strong>, which allows signaling to clients the preference for IPv6. At the same time, mechanisms such as NAT64<\/strong>, CLAT<\/strong>, and the 464XLAT<\/strong> model make it possible to access IPv4 resources from IPv6-mostly networks.<\/p>\n\n\n\n

IPv6-Mostly Versus IPv6-Only<\/h2>\n\n\n\n

An IPv6-only<\/strong> network has a clear architectural feature: the host receives exclusively IPv6 addressing and does not have native IPv4 connectivity. When an application needs to access resources that still use IPv4, this communication takes place through translation mechanisms.<\/p>\n\n\n\n

The most common model for this scenario is 464XLAT<\/strong> (RFC 6877). In this model, there are two main components:<\/p>\n\n\n\n