quote of the day... when e1 and e2 matter...

from odom, ccnp route...

The benefits of the different external route types apply mostly to when multiple ASBRs advertise the same subnet. For example, imagine two ASBRs, ASBR1 and ASBR2, between OSPF and another routing domain. If the goal is to always send traffic through ASBR1,
you could use E2 routes and set the metric for ASBR1’s redistributed routes to a lower metric than ASBR2. Because routers ignore the internal metrics when calculating the E2 metrics, then every router will choose ASBR1 as the better ASBR. Conversely, if the goal were
to balance the traffic, and make each router pick the closest ASBR, both ASBRs could set the same metric to their redistributed routes, but make the routers Type E1. As a result, routers closer to each ASBR choose best routes based on the lower OSPF internal costs. Also, note that for a given prefix/length, OSPF always prefers an E1 route over an E2 route.