/var/named/cluster.arpa.zone

$TTL 86400 ; 1 day @ IN SOA cluster. root.bert.cluster. ( 51 ; serial 8h ; refresh (8 hours) 2h ; retry (2 hours) 1w ; expire (1 week) 86400 ; minimum (1 day) ) cluster. IN NS bert.cluster. 1 IN PTR bert.cluster. 2 IN PTR gus.cluster.