Enable the overlay in Portage:
mkdir -p /etc/portage/repos.conf; curl -o /etc/portage/repos.conf/stintel.conf https://www.linux-ipv6.be/stintel.conf
Disclaimer
The contents of this overlay are provided "as is", without warranty of any kind, express or implied, including but not limited to the warranties of merchantability, fitness for a particular purpose and noninfringement. In no event shall the authors or copyright holders be liable for any claim, damages or other liability, whether in an action of contract, tort or otherwise, arising from, out of or in connection with the software or the use or other dealings in the software.
Limitation of Liability
In no event shall the authors or copyright holders be liable for any special, direct, indirect, consequential or incidental damages or any damages whatsoever resulting from loss of use, data or profits, whether in an action of contract, negligence or other tortious action, arising out of or in connection with the use or performance of the overlay, even if the authors have been advised of the possibility of such damages.
Third-Party Software
Some parts of this overlay may include third-party software. The inclusion of any software does not in any way imply that the authors or copyright holders endorse or support such software. Any use or distribution of such third-party software is governed by the applicable open-source license for that software, if available.