If you're trying to perform validation, why not just use the facility designed for that?

use Moose::Util::TypeConstraints;

subtype 'Net::IP::Address',
   as 'Str',
   where { NetAddr::IP->new($_, '255.255.255.255') };

no Moose::Util::TypeConstraints;
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has [ qw/server peer monitor netlog/ ] => (
   is       => 'ro',
   isa      => 'Net::IP::Address',
   required => 1,
);
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