Showing results for 
Search instead for 
Did you mean: 


Why use type-E2 OSPF external routes with one ASBR???

Say I have an external type 2 LSA injected into area 0.

Router 5 (not the ASBR) sits somewhere within area 0 and has 2 different possible paths to reach the ASBR.

When it look at its LSDB it will determine that interface fa0/0 is closer (has a better metric) to the ASBR than interface fa0/1.

The metric to get the external network is the same out of either interface (because it is a E2 Type 5 LSA) but it picks fa0/0 as the outgoing interface because it has a better path to the ASBR.

Isn't this essentially the same as a E1 Type 5 LSA? I understand that the metric in the routing table will differ in both instances (E2 will remain the same as what the Type 5 LSA states, whereas the E1 entry will read "Type 5 LSA metric PLUS metric to reach ASBR"). But what does this really matter if the outgoing interface is the closest one to the ASBR? Should the router not equal cost load balance between the two paths to the ASBR given the identical metrics?

I understand that, in instances where there are 2 ASBRs, setting different E2 metrics per ASBR can cause one to be preferred over another. But in the case of a single ASBR ... if an E2 tie breaker is to use the very thing that makes it seperate from an E1, why use it if you have just one ASBR?

Everyone's tags (4)
CreatePlease to create content
Content for Community-Ad