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The importance of these addresses is that they cannot be reached from the global Internet. If you are trying out the code in this book on a machine that has an address in the private-use class (e.g., on your home network), and you are trying to communicate with another host that does not have one of these addresses, in general you will not succeed unless the host with the private address initiates communication—and even then you may fail.

A related class contains the link-local, or “autoconfiguration” addresses. For IPv4, such addresses begin with 169.254. For IPv6, any address whose first 16-bit chunk is FE80, FE90, FEA0, or FEB0 is a...

From

Cover of TCP/IP Sockets in C, 2nd Edition

Note

private address