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2.6.2.2.2. 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 client-1.example.com, but deny connections from client-2.example.com:
sshd : client-1.example.com : allow
sshd : client-2.example.com : 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.