Single machine — A fully qualified domain name (that can be resolved by the server), hostname (that can be resolved by the server), or an IP address.
Series of machines specified with wildcards — Use the * or ? character to specify a string match. Wildcards are not to be used with IP addresses; however, they may accidentally work if reverse DNS lookups fail. When specifying wildcards in fully qualified domain names, dots (.) are not included in the wildcard. For example,
*.example.com includes one.example.com but does not include one.two.example.com.
IP networks — Use a.b.c.d/z, where a.b.c.d is the network and z is the number of bits in the netmask (for example 192.168.0.0/24). Another acceptable format is a.b.c.d/netmask, where a.b.c.d is the network and netmask is the netmask (for example, 192.168.100.8/255.255.255.0).
Netgroups — In the format @group-name, where group-name is the NIS netgroup name.