Loopback is defined in RFC 5735 as a Global and Other Specialized Address Blocks stating: - This block is assigned for use as the Internet host loopback address. A datagram sent by a higher-level protocol to an address anywhere within this block loops back inside the host. This is ordinarily implemented using only for loopback. As described in RFC 1122, Section, addresses within the entire block do not legitimately appear on any network anywhere.

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