Refer to the following diagram of an OSPF network. Which of the following routers generate network link advertisements (NLA)? (Choose all that apply.)

Refer to the following diagram of an OSPF network.

300-410 Part 04 Q09 050

300-410 Part 04 Q09 050

Which of the following routers generate network link advertisements (NLA)? (Choose all that apply.)

  • R3
  • R4
  • R7
  • R8
  • R9
  • R13
Explanation:
The R3 and the R9 routers in the scenario generate network link advertisements (NLA). An NLA or a Type 2 LSA is generated only by the designated router (DR) of a segment. Type 2 LSAs are generated only for those networks in which a DR has been selected. A DR is a router that has the highest OSPF priority on a segment. Until there are two OSPF routers on the segment, no Type 2 LSAs will be generated.Type 2 LSAs are flooded in the area that contains the network segment with the DR. These advertisements are used by the DR to represent the routers that are connected to the network. This type of LSA is sent to those routers that belong to the same network as the DR. Therefore, in this case, Type 2 LSAs are generated by the R3 and the R9 routers. R3 sends the LSAs to R1, R2, and R4, while R9 sends LSAs to R8, R10, and R11.R4, R7, or R8 will not send NLAs or Type 2 LSAs. These three routers are area border routers (ABR) for different OSPF areas. Like any other OSPF router, these routers generate Type 1 LSAs or router link advertisements (RLA). The LSAs contain the state of the routers that belong to same area. In this case, R4 generates and floods Type 1 LSAs into Area 0 and Area 10. Similarly, R7 and R8 flood Type 1 LSAs into Area 0 and Area 20, and Area 0 and Area 30, respectively.ABRs also generate Type 3 and Type 4 LSAs or summary link advertisements (SLA). These LSAs are flooded into other areas to and from the backbone area. Type 3 LSAs contain the list of networks that are exchanged between two areas. In this case, R4 floods Type 3 LSAs into Area 0 and Area 10; R7 floods these LSAs into Area 0 and Area 20; and R8 floods them into Area 0 and Area 30. Type 4 LSAs list the routes that point to autonomous system boundary router (ASBR).R13 will not generate Type 2 LSAs. R13 is an Area System Border Router (ASBR), which generate Type 5 LSAs apart from Type 1 LSAs. Type 5 LSAs, or external link advertisements, list the routes external to the AS; they are flooded throughout the OSPF domain except for stub areas.

Objective:
Layer 3 Technologies
Sub-Objective:
Configure and verify network types, area types, and router types

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