while (<CONF>) {
  if ( /^interface (\S+)/ ) {
    $cur_int = $1;
    $int{$cur_int}{ip}="";
  }
  elsif ( /^ ip address ([\d\.]+) ([\d\.]+)$/ ) {
    my ( $ip, $mask ) = ( $1, $2 );
    $int{$cur_int}{ip}=MyIP->new($ip, $mask)
        or die "incorrect IP address: $ip $mask\n";
    print "$cur_int: $ip $mask = ", $int{$cur_int}{ip}->print_cidr(), "\n";
  }
}