While BIND 9.18.21 with "qname-minimization strict;" SERVFAILs on the following query, dig with +trace resolves it. Just a data point, and if they fix their s**t and stop impersonating a signed zone then presumably the example will resolve itself (pun intended).
dig -x 131.191.85.31 dig -x 131.191.85.31 +trace -- Fred Morris -- Visit https://lists.isc.org/mailman/listinfo/bind-users to unsubscribe from this list ISC funds the development of this software with paid support subscriptions. Contact us at https://www.isc.org/contact/ for more information. bind-users mailing list bind-users@lists.isc.org https://lists.isc.org/mailman/listinfo/bind-users
