This option specifies the list of IPs authorized to ask for dns zone transfer from bind DLZ module. The IP list is comma and space separated and specified in the same syntax as used in , specifically including IP address, IP prefixes and IP address masks. As this is a DNS server option, hostnames are naturally not permitted. The default behaviour is to deny any request. A request will be authorized only if the emitting client is identified in this list, and not in 192.168.0.1