sub new
{
  ...
  $self = {
      ...
      _IP => undef,
      ...
  }
  bless ($self, $class);
  return $self;
}

sub set_ip
{
  my ($self,$ip) = @_;
  $self->{_IP} = new Net::IP($ip) or die (Net::IP::Error());
}

##</code><code>##

if(grep($_ == $ref, @{$self->{_ancestors}}));