Ospf new dynamic route learnt

[IrmanGhaffar]

Hi all, 

  Hope someone can shed some light on a perplexing issue Iam having with ospf.

So I have a router with 2 peers (asbr's) connected to bgp peers further upstream into mpls.

If I am learning a prefix from peer 1 all is good and well, now let's say several hours later peer 2 also learnt the same route from upstream mpls.

It's come into my routers ospf database and has a better metric than the one my router already installed in its route table via peer 1.

Should the routing table discard the route to the prefix via peer1 and now install the route via peer 2?

I thought it should but seems the update is not dynamic by nature... 

Has anyone else come across this problem?

Thanks all

[paul driver]

Hello

The question however does remain, why would an OSPF E2 route with a cost of 255 remain in the routing table when there there is another OSPF E2 route with a cost of 1 available?

when your redistributing onto ospf from multiple exit points it will depend on not only the metric type from each asbr but also the internal cost towards the asbr and also any abr in the asbrs path.

As such my understanding is even with type 2 external routes the cost path towards the asbr will be still be internally calculated 

Check the path metric towards the asbr’s and you will most properly find out why ospf is selectiing that path-

show ip ospf database external  x.x,xx

show ip ospf database asbr- summary xxxx

show ip ospf database router xxxx 

[IrmanGhaffar]

Hey Paul,

  I think I managed to solve it.... The problem appeared to be running 2 OSPF processes on the same physical device. From my testing, the route that made it into the RIB first will remain, regardless of metrics. I did test this in a situation where everything is in the same area and it worked as expected, the metric was used to calculate the best path. As soon as I add in multiple processes the metric goes out the window.

Let me know if you would agree with my testing. If not I can show the outputs.

Thanks for all your help.