Your area border router (ABR) receives type 1.2 and 5 link-state advertisements (LSAs) from a non-backbone area.
What would the ABR do with the information learned from the non-backbone area?
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A. B. C. D.C
Link-state routing protocols, such as OSPF (Open Shortest Path First), use a link-state database to maintain a map of the network topology. Each router floods its link-state information in the form of LSAs to its neighboring routers, which in turn flood the LSAs to their neighbors, and so on. All routers in the network build their link-state database based on the received LSAs, and then run the Dijkstra algorithm to compute the shortest path to all destinations.
An area is a logical grouping of routers and networks that share the same topological information. The backbone area (area 0) is a special area that connects all other areas in OSPF. Area border routers (ABRs) connect multiple areas, and maintain separate link-state databases for each area they are connected to.
There are several types of LSAs in OSPF, and each type serves a specific purpose. Type 1 LSAs describe the router itself, its interfaces, and the links to its directly connected networks within the same area. Type 2 LSAs describe the transit networks (e.g., Ethernet, Frame Relay) that interconnect routers within the same area. Type 3 LSAs describe the routes to networks outside the local area but within the same OSPF domain. Type 4 LSAs describe the ASBR (Autonomous System Boundary Router) that connects to an external routing domain. Type 5 LSAs describe the routes to networks outside the OSPF domain.
Now, let's get back to the question. The ABR in the question receives type 1.2 and 5 LSAs from a non-backbone area. This means that the ABR learns about a new router (type 1.2) and about routes to external networks (type 5) in the non-backbone area.
Option A: The ABR will generate type 2 and 3 LSAs and flood type 5 LSAs to the backbone area. This option is incorrect because it mentions type 2 LSAs, which are used only within an area to describe transit networks, and do not need to be flooded to the backbone area. Also, it does not mention type 1.2 LSAs, which the ABR received from the non-backbone area.
Option B: The ABR will generate only type 3 LSAs and flood only type 5 LSAs to the backbone area. This option is also incorrect because it does not mention type 1.2 LSAs, which the ABR received from the non-backbone area. Also, it does not mention type 4 LSAs, which may be necessary if the non-backbone area has an ASBR.
Option C: The ABR will generate type 3 and 4 LSAs. And flood type 5 LSAs to the backbone area. This option is the correct answer. The ABR will generate type 3 LSAs to describe the routes to external networks learned from the non-backbone area, and type 4 LSAs if the non-backbone area has an ASBR. It will flood these LSAs to the backbone area, which will then compute the shortest paths to these networks.
Option D: The ABR will generate only type 4 LSAs and flood only type 5 LSAs to the backbone area. This option is incorrect because it does not mention type 1.2 and 3 LSAs, which may be necessary to describe the local topology and the routes to networks within the OSPF domain, respectively.