I upgraded from 5.8 to 5.14 when I noticed that the change log mentioned supporting IPv6 prefix pools for ppp.
Sure enough, I added a /48 to my tunnelbroker.net tunnel and assigned it to an IPv6 pool and assigned that as the prefix pool for my ppp profile, and it works with my mac, provided I give it a little bit of help.
sysctl -w net.inet6.ip6.accept_rtadv=1
is required before bringing up the link, and
route add -inet6 default -interface ppp0
is required after bringing up the link. But if I do those two things, I can, indeed, reach the greater IPv6 Internet. Yay!
The only question is, does anyone know if there’s some way to tweak OS X so that these manual steps are not required?