nospoof
Valid values are on and off. If set to on, the resolv+
library will attempt to prevent hostname spoofing to enhance
the security of rlogin and rsh. It works as follows: after
performing a host address lookup, resolv+ will perform a
hostname lookup for that address. If the two hostnames do not
match, the query will fail. The default value is off.
man /etc/host.conf:
This option is missing in host.conf.