I used to use these two services together do this: https://puck.nether.net/dns https://acc.rollernet.us/ They're both free to sign up, provide free second

I used to use these two services together do this: https://puck.nether.net/dns https://acc.rollernet.us/ They're both free to sign up, provide free secondary DNS, zone transfers and fully support IPv6. I only stopped using them because I wanted to run my own DNS service.