This post has been in my drafts folder since I first set up 6rd on OPNsense 18.7 in August 2018. The 6rd implementation has not been painless: I completely lost all internet connectivity when upgrading to 19.1. 6rd has stopped working again on 19.7. At the time of publishing this post, I am in the process of replacing OPNsense with the Ubiquiti EdgeRouter 4. I’m hoping it will be more stable.