DNS Zone Audit

Audit a DNS zone against the rules that make a zone illegal or make it quietly not work. Reports a CNAME at the apex, which is forbidden because the apex must also carry SOA and NS; a CNAME alongside any other record type; an MX, NS or CNAME pointing at a name that is itself a CNAME, whose failure is intermittent rather than total; a target inside the zone the zone does not define; a cyclic CNAME chain; TTLs that differ within one record set; and a record outside the zone.