Hi @wilder7bc,
If you redistribute something into OSPF, the E2 route will have a fixed metric, the E1 route will have a metric that increases throughout the network, it’s the same as with normal OSPF routes.
So why do they use E2 vs E1? Let’s look at some examples. Let’s say the red box is OSPF and blue is some other routing protocol.
Scenario 1
There is only one router doing redistribution so it doesn’t matter what the metric is…you can only go through R1 if you want to get to the other side. You can use either E2 or E1, it doesn’t matter.
Scenario 2
Here we have R3 and R4 doing redistribution. If you use E2 here, the metric for the redistributed routes is the same everywhere in the OSPF domain. That means that R1 will use R3 and R4 to get to any redistributed route. It works, but it’s not optimal…R4 is located one hop further away from R1 compared to R3. In this case, it’s better to use E1 since it metric increases throughout the domain.
Hope this helps!