Red Hat Training

A Red Hat training course is available for Red Hat Enterprise Linux Access Control

Option fields also allow administrators to explicitly allow or deny hosts in a single rule by adding the allow or deny directive as the final option.
For example, the following two rules allow SSH connections from, but deny connections from
sshd : : allow
sshd : : deny
By allowing access control on a per-rule basis, the option field allows administrators to consolidate all access rules into a single file: either hosts.allow or hosts.deny. Some administrators consider this an easier way of organizing access rules.