Maybe you are wrong. or may be I am but:
gethostbyaddr returns the names matching the ip. reverse name entries is as secure as dns gets. if the ip has a reverse name, the ip for that name will match the ip.
the discussion in the Cookbook is about looking, whether the ipaddress you got when looking up by name, matches the original name. which it will not, unless you have a reverse entry for the same name.

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