I know my ISP provides IPV6. It was previously broken, but restarting my router fixed it. I confirmed my IPV6 connectivity on several websites. Then I restarted Bitcoin Core so it would see the new IPV6 address on startup, but bitnodes.21.co says my IPV6 address can't be reached. Any advice?
Normally it should autodetect. Check for lines like these in debug.log:
If that's the case, Bitcoin Core is listening to it, and if another service can't reach it, it may be a network configuration problem or a problem with that service.
If it isn't, you can manually bind to an IP address (IPv4 or IPv6) using the