Which LSA packet types are originated only by an OSPF ABR router?
Click on the arrows to vote for the correct answer
A. B. C. D.B
In Open Shortest Path First (OSPF) protocol, the Autonomous System Boundary Router (ABR) is a router that connects two or more OSPF areas and forwards traffic between them. An ABR originates and floods various types of Link State Advertisements (LSAs) to share routing information across the OSPF network.
The LSA packet types that are originated only by an OSPF ABR router are:
A. Type 2 and Type 3
Type 2 LSAs are generated by an ABR to advertise the summary of networks that exist in other OSPF areas. The ABR generates a Type 2 LSA for each area to which it is connected. The Type 2 LSA is flooded within the area where it is originated and also propagated to other areas through the backbone area.
Type 3 LSAs are generated by an ABR to advertise the summary of routes from other OSPF areas to the backbone area. The ABR generates a Type 3 LSA for each prefix that it is advertising from another area to the backbone. The Type 3 LSA is flooded throughout the backbone area and to all other areas.
Therefore, option A is correct.
B. Type 3 and Type 4
Type 4 LSAs are generated by the ASBR to advertise the external routes that it is redistributing into OSPF. Type 4 LSAs are flooded only within the area where the ASBR is located.
Since Type 4 LSAs are originated by the ASBR, not by the ABR, option B is not correct.
C. Type 5 and Type 6
Type 5 LSAs are generated by the ASBR to advertise the external routes that it is redistributing into OSPF. Type 5 LSAs are flooded throughout the OSPF domain, including all areas and the backbone.
Type 6 LSAs are generated by the NSSA ABR to advertise the external routes that it is translating into NSSA type 7 LSAs. Type 6 LSAs are flooded only within the NSSA area.
Therefore, option C is not correct.
D. Type 6 and Type 7
Type 7 LSAs are generated by the NSSA ASBR to advertise the external routes that it is redistributing into the NSSA. Type 7 LSAs are flooded only within the NSSA area.
Since Type 7 LSAs are originated by the NSSA ASBR, not by the ABR, option D is not correct.
In conclusion, option A is the correct answer.