What are LSA in OSPF?
From Wikipedia, the free encyclopedia. The link-state advertisement (LSA) is a basic communication means of the OSPF routing protocol for the Internet Protocol (IP). It communicates the router’s local routing topology to all other local routers in the same OSPF area.
What are OSPF area types?
There are five types of OSPF areas: Backbone area (area 0), Standard area, Stub area, Totally stubby area, and No so stubby area (NSSA).
Which LSA present in OSPF stub area?
Stub areas can contain type 1, 2, and 3 LSAs. A default route is substituted for external routes. Totally stubby areas can only contain type 1 and 2 LSAs, and a single type 3 LSA. The type 3 LSA describes a default route, substituted for all external and inter-area routes.
What are the different types of LSA in OSPF?
Within OSPF there are a number of LSA types. Below provides the main types: Generated by each internal router within an area, per area link. Flooded within a single area only. Generated by the DR. Flooded within a single area only. Generated by the ABR. Describes inter-area routes.
When to use special area types in OSPF?
These special area types are used to insert default routes into an area and replace type 3 summary LSAs and type 5 external LSAs. This will keep the LSA flooding to a minimum, LSDB smaller, less SPF calculations and a smaller routing table. Let me give you an overview with the different stub areas:
Can a stub area receive a type 5 LSA?
With stub areas, the Type 5 LSA is not sent by the ABR. Instead, the Type 3 LSA includes a default route which it sends out to the stub area nodes. Figure 4: Stub OSPF area. Totally stubby areas are similar to stub areas, in the fact that they do not receive type 4 or 5 LSAs from their ABRs.
Can you have an ASBR in OSPF stub area?
All the prefixes that you redistributed into OSPF from another routing protocol are not welcome in the stub area. Since you are not allowed to have type 5 external LSAs in the stub area it’s also impossible to have an ASBR in the stub area. In order to reach networks in other areas there will be a default route.