Thank you for that nugget of wisdom. It's good to know if IP6 is needed. Replacing IO::Socket::INET with IO:Socket::IP only requires a slight change to the settings:

IO::Socket::INET 

   Reuse => 1,

Becomes:

IO::Socket::IP

   ReuseAddr => 1,
   ReusePort => 1,

corelist IO::Socket::INET
IO::Socket::INET was first released with perl v5.6.0 (2000-Mar-22)

corelist IO::Socket::IP
IO::Socket::IP was first released with perl v5.19.8  (2014-Jan-20)

OTOH IO::Socket::INET buys 14 years of backwards compatability:

Don't be so sure. Just because it buys you 14 years of being in core doesn't mean that much. The current version of IO::Socket::IP has full test passes on perls as old as 5.8.1, so you are only buying something like three and a half years of extra backwards compatibility. Contrast that with how much forwards compatibility you would be buying with IO::Socket::IP in terms of transparent IPv6 support.

OTOH IO::Socket::INET buys 14 years of backwards compatability

I'm aware of that. But frankly, any system too old to run at least Perl 5.20 with IO::Socket::IP and IPv6 (at least have support for it) is probably a major security disaster waiting to happen. For one thing, it probably still uses SSLv1 or no encryption at all.

I know there are always legitimate business reasons to run such old systems, but these days they they become overshadowed by the risk involved. Just thinking of Facebook here. Because they didn't patch a data leak when they first noticed the possibility, they might have to pay the EU a penalty of over a billion Euros. And thats just the government side, civil lawsuits may follow. That was a somewhat recent security issue, i somewhat doubt government would be more lenient if you run code that has issues for which patches are out for over a decade...

"For me, programming in Perl is like my cooking. The result may not always taste nice, but it's quick, painless and it get's food on the table."

Thanks for pointing out the limitations of IO::Socket::INET vs IO::Socket::IP. I have experience writing secure web applications. These modules are also used in desktop applications to provide the controller for Perl models viewed in a web browser. In such cases network encryption is irrelevant and compatability and portability are the ultimate goals.

I like to use Perl::MinimumVersion to see how far back my code can be pushed without breaking. :-)