With the IPv6-only option, a host can indicate that it supports operation in an IPv6-only network. This is useful in combination with 464XLAT CLAT: IPv4 applications can connect to legacy addresses using a NAT64 gateway provided by the network. In this situation, the host can operate without IPv4 addresses assigned, and all network traffic is IPv6, without loosing connectivity to IPv4 hosts.

NetworkManager currently does not support CLAT, and thus, this new option is disabled by default. Various CLAT implementations exist (jool – out-of-mainline kernel module, upstreaming not planned; tayga – unmaintained userspace application, potentially performance issues), but are not suitable as a general solution.

An eBPF-based CLAT is already being worked on. Hopefully, we can see full IPv6-only support soon! This will enable IPv6-only home networks for the average user, assuming the ISP provides a NAT64 gateway. Connections to IPv4 hosts can be established using the NAT64 gateway, without any IPv4 connections in the local network or directly to the internet. For legacy devices in the local network, IPv6-mostly networks still provide local IPv4 connections.