[CentOS] tcpwrappers hosts.allow netmask problem

I can't seem to get netmask notations to work in /etc/hosts.allow on
my Centos 4.4 systems.  The docs seem to indicate that network
specifications like 192.168.100.0/24 or 192.168.100.0/255.255.255.0
should work.  However, I can only get networks specified like
192.168.100. to work.

Anyone know what I'm missing?

Thanks,
Tom