An OSPF route won't appear in the routing table though it exists in LSDB and forward address is reac

I encountered a situation where an OSPF External route won't appear in the routing table even though it exists in LSDB and the forward address is reachable.

 

My understanding is OSPF Type-5 external routes won't get into the routing table if:

  - Forward Address is set AND

  - The forward address is not reachable

 

To prove the above, I set up the following OSPF areas where a router in Area 1 receives a default route via BGP.

[BGP] -- [Area 1] -- [Area 0] -- [Area 2]

*Note OSPF is enabled on the WAN interface in addition to BGP though there's no OSPF neighbor in that direction for the sake of experiment. (Without it, the Forward Address is not set.)

 

In this state, I checked the routing table on a router in Area 2 and, as expected, found the default route installed as OSPF E2.

 

Next, I set up a filter on ABR between areas 0 and 1 so that the forward address for the default route won't be propagated into Area 0.

area 1 range 12.12.12.0 255.255.255.0 not-advertise  (12.12.12.0 is the WAN link address and forward address for the default route)

 

After this, the default route is gone from the routing table although it's still in LSDB.  That's because there's no reachability to the Forward Address.


In order to make the Forward Address reachable, I added a static route for the forward address on every router in Area 0 and Area 2 (except for the ABR between Areas 1 and 0).  I thought this will bring the default route back into the routing table on Area 2 routers, but it DIDN'T.


I can ping and traceroute to the forwarding address but still the default route won't appear in the routing table.

Can anyone explain why?

Also, how can I bring the default route back into Area 2 routers without removing the filter (i.e., area 1 range 12.12.12.0 255.255.255.0 not-advertise).

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