Your code doesn't work because you're passing a hostname to inet_ntoa; it expects an ip address packed into four characters.

I think you probably misread this example:

($port, $iaddr) = sockaddr_in(getpeername(Socket_Handle));
$peer_host = gethostbyaddr($iaddr, AF_INET);
$peer_addr = inet_ntoa($iaddr);
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Note that $iaddr, not the return value of gethostbyaddr, is passed to inet_ntoa. What you want can be reduced to a single line:

(gethostbyaddr(gethostbyname($ipaddr), AF_INET))[0]
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hdp.

p.s. chomp $ipaddr or it'll continue to fail, but in a new and interesting way!