An introduction to TCP Wrappers
The basic idea of TCP Wrappers is to provide wrapper daemons that can be installed without any changes to existing software. Most TCP/IP applications depend on the client/server model: that is, when a connection is requested by a client, a server process is started on the host to deal with this. TCP Wrappers works by interposing an additional layer, or wrapper, between client and server. In the basic service, the wrapper simply logs the name of the client host and of the requested service, then hands over to the real daemon, neither exchanging information with the client or server, nor imposing overhead on the actual conversation between the two.
By Paul Dunne at Linux, Unix, /etc/.
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