Note: A 2022 tutorial on the many aspects of IPv6 can be found in this All Things TECH IPv6 on Mac OS article.
In Apple macOS (all versions), OS X (all versions), and Mac OS X (versions 10.3 Panther and later), Internet Protocol version 6 (IPv6) is on by default. It was also supported in Mac OS X versions 10.0 Cheetah, 10.1 Puma, and 10.2 Jaguar, but turned off by default.
This article describes how to turn off IPv6 using Network settings or the command line.
If neither the Network settings nor the command line as described in the above article work, another command to turn off IPv6 on all network interfaces is
If either of the following variables are defined in /etc/sysctl.conf, delete them (no matter what value they have):