+------+      +------+
          | AS a |------| AS c |
          +------+      +------+
          with ROA         |
          +------+      +------+      +------+
          | AS b |------| AS d |------| AS e |
          +------+      +------+      +------+
        without ROA   ROV-disabled   ROV-enabled
                   
Figure 3: an example scenario of implicit route filtering