IPv6 DNS glue records

 http://www.networksolutions.com/support/Adding-an-IPv6-record/

 “To specify your IPv6 name server address (IPv6 glue record), e-mail us the domain name, the host name of the name server(s), and their IPv6 address(es).”

 https://www.internic.net/whois.html

 http://www.intodns.com/

 https://mebsd.com/glue

 http://www.webdnstools.com/dnstools/domain_check