Advanced OSPF Notes

Always check your OSPF neighbors. I had a problem injecting a default route into NSSA totally stub area, and I figured out it was a problem of OSPF network types.R3 and R4 were not already OSPF Neighbors. They are connected through Frame relay. R3 interface is “point-to-point” OSPF network type. R4 however, has interface ser0/0 in “NBMA” OSPF Network type.I corrected the network type under ser0/0 of R4 and it works
– Redistributed routes that are coming from area 0 are not injected into NSSA (neither into stub areas).This is a nice post by Peter Paluch about interpreting OSPF database.

show-ip-ospf-database-1

Show ip ospf database

NSSA and default route 

The default behaviour in NSSA is: no default route is injected by the NSSA ABR:

show-ip-route-1

show ip route

 

Routes are inserted normally.

Use of “default-information-originate” on an NSSA ABR to inject a default route into NSSA:

show-ip-ospf-database-2

show ip OSPF database

 

 

 

 

 

 

 

 

We know that, an NSSA ASBR injects LSA7 into NSSA. Why is R3 an ASBR?

 

 

 

 

 

 

 

RIB on R4:

 

 

 

 

 

 

 

Use of “no-summary” on NSSA ABR to inject a default route into NSSA:
No-summary is set on R3. OSPF database on R4 has shrinked:

 

 

 

 

 

RIB on R4:

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