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Absolute FreeBSD, 2nd Edition by Michael W. Lucas

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TCP Wrappers

Remember from Chapter 6 that network connections are made to various programs that listen for connection requests. When a program is built with TCP wrappers support, the program checks the incoming request against the wrappers configuration. If the wrappers configuration says to reject the connection, the program immediately drops the request. Despite the name, TCP wrappers work with both TCP and UDP connections. Wrappers are a long-running Unix standard that have been incorporated into FreeBSD. Individual programs might or might not work with wrappers; while just about everything in the base FreeBSD system does, some third-party software doesn't.

TCP wrappers are implemented as a shared library, called libwrap. As we'll see in Chapter 12 ...

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