linuxtoys.net), but it is more often a wildcard variation that specifies an entire
range of addresses. A client entry can take four different forms. The online manual page for the
hosts.allow file describes them as follows:
A string that begins with a dot (.) character. A hostname is matched if the last components
of its name match the specified pattern. For example, the pattern .tue.nl matches
the hostname wzv.win.tue.nl.
A string that ends with a dot (.) character. A host address is matched if its first numeric
fields match the given string. For example, the pattern 131.155. matches the address of
(almost) every host on the Eindhoven University network (131.155.x.x).
A string that begins with an at (@) sign is treated as an NIS netgroup name. A hostname is
matched if it is a host member of the specified netgroup. Netgroup matches are not supported
for daemon process names or for client user names.
An expression of the form n.n.n.n/m.m.m.m is interpreted as a net/mask pair. A host address
is matched if net is equal to the bitwise and of the address and the mask. For example, the
net/mask pattern 131.155.72.0/255.255.254.0 matches every address in the range
131.155.72.0 through 131.155.73.255.
The example host.allow contains the first two types of client specification.
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