Enabling an IPv6-only network using Internet Sharing on El Capitan
One of the hidden features of OS X El Capitan is the ability to enable Internet Sharing to provide only IPv6 addresses. This feature was added to El Capitan to help developers ensure their apps are ready to work with IPv6. It uses NAT64, which facilitates communication between IPv6 and IPv4 hosts by using a form of NAT.
For those interested in having the ability to set up an IPv6-only network, see below the jump for the procedure.
A Mac running OS X 10.11.x
1. Open System Preferences
2. Option-click on the Sharing preference pane
3. A Create NAT64 Network checkbox will appear (this may also be labeled Create IPv6 Only Network.)
4. Check Create NAT64 Network.
5. Select the interface to share out over
6. Check the Internet Sharing checkbox
7. When prompted, click the Start button
8. An IPv6-only network should now be available.