21.15.204.in-addr.arpa is delegated to two nameservers, however both delegated nameservers are missing in the zone and two other nameservers are listed instead. Two nameservers have the same IP number. All of them are on the same IP network. tfbnw.com, tfbnw.net, fbcdn.net, fbhigh.net, tfbnet.net and at least 26 other hosts share nameservers with this domain.