Blacklist

By blacklisting what is meant is that by policy everything is allowed with individual policies in place to deny someone. In IP firewalling one can use blacklisting to deny one or more IP's. In OpenBSD's spamd a large list of Chinese and Korean IP blocks have been installed to blacklist these IP's without allowing them to be greylisted. In TCP Wrappers the blacklist is in /etc/hosts.deny.