TCP Wrappers for service restrictions

REF: https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/3/html/Reference_Guide/s1-tcpwrappers-access.html

The following is a list of the most common accepted patterns for a client list entry:

• Hostname beginning with a period (.) — Placing a period at the beginning of a hostname, matches all hosts sharing the listed components of the name. The following example applies to any host within the example.com domain:

  ALL : .example.com

• IP address ending with a period (.) — Placing a period at the end of an IP address matches all hosts sharing the initial numeric groups of an IP address. The following example applies to any host within the 192.168.x.x network:

  ALL : 192.168.

• IP address/netmask pair — Netmask expressions can also be used as a pattern to control access to a particular group of IP addresses. The following example applies to any host with an address of 192.168.0.0 through 192.168.1.255:

  ALL : 192.168.0.0/255.255.254.0