chomp is needed (if the IP address is the last text on the line after the split), but it may not be a complete solution to your problem. Consider the following code:

use warnings;
use strict;
use Data::Validate::IP qw(is_ipv4);

while (my $line = <DATA>) {
    chomp $line;
    my($key, $parameter_value) = split("=", $line);
    if (is_ipv4($parameter_value))
    {
      print $parameter_value;
    }
    else {
      print "Fail"
    }
}
print "\n";

__DATA__
abc=1.2.3.4
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It prints "1.2.3.4". If you comment out the chomp line, it prints "Fail".

Maybe $parameter_value isn't what you think it is. Tip #2 from the Basic debugging checklist: print

    my($key, $parameter_value) = split("=", $line);
    print ">>>$parameter_value<<<\n";
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