350-401 · Question #306
Which statement about Type-4 LSA in OSPFv2 is true?
The correct answer is B. It is generated by each ABR and forwarded in non-stub areas.. Type 4 LSAs (ASBR-Summary LSAs) are generated by Area Border Routers (ABRs) to advertise the location of an ASBR to other non-stub areas within the OSPF domain.
Question
Which statement about Type-4 LSA in OSPFv2 is true?
Options
- AIt is present only in the backbone area.
- BIt is generated by each ABR and forwarded in non-stub areas.
- CIt is forwarded in NSSA areas.
- DIt is generated by the ASBR and forwarded throughout the whole OSPF domain.
How the community answered
(29 responses)- B90% (26)
- C3% (1)
- D7% (2)
Why each option
Type 4 LSAs (ASBR-Summary LSAs) are generated by Area Border Routers (ABRs) to advertise the location of an ASBR to other non-stub areas within the OSPF domain.
Type 4 LSAs are not present only in the backbone area; they are generated by ABRs and flooded into all other non-stub areas.
Type 4 LSAs, known as ASBR-Summary LSAs, are generated by an Area Border Router (ABR) that connects to an area containing an Autonomous System Border Router (ASBR). The purpose of this LSA is to advertise the ASBR's IP address to all other non-stub OSPF areas, allowing routers in those areas to compute a path to the ASBR so they can then reach external destinations advertised by the ASBR in Type 5 LSAs.
Type 4 LSAs are typically not flooded *into* NSSA areas from the backbone or other areas, similar to how Type 5 LSAs are excluded. NSSA areas handle external routes via Type 7 LSAs.
Type 4 LSAs are generated by the *ABR* that is connected to the area where the ASBR resides, not by the ASBR itself. The ASBR generates Type 5 LSAs for external routes.
Concept tested: OSPFv2 LSA Type 4 characteristics
Source: https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/13689-18.html
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