I just made an interesting discovery whilst playing with routing metrics on my Lab rack. There's a myth going about that two competing E2 routes for a prefix with be selected by first comapring the metric inserted by the originating ASBR. If that metric is equal for both routes (e.g. it has value 20 by default), then the forwarding metric to reach the ASBR is used to select the best route.
The second point is not entirely true. It seems that if one route to reach the ASBR is intra-area and the other is inter-area, then the intra-area router will be preferred even if it bears a higher forwaridng metric than the inter-area route.
So forwarding metric 129 can beat a competing route with forwarding metric of 128 to reach the ASBR providing the first is an intra-area route and the second is inter-area.
Comments?
johnsg