Authentic Huawei Certification Exam H12-831_V1.0 Questions Answers

Comprehensive and Detailed In-Depth Explanation:To determine whether the statement is true or false, we need to analyze the OSPFv3 topology, the role of area types, and the behavior of Inter-Area-Prefix-LSAs. Let’s break it down step by step:

Understanding the OSPFv3 Topology and Area Types:

The figure shows three routers (R1, R2, and R3) connected in an OSPFv3 network. R1 and R2 are in Area 0 (the backbone area), while R2 and R3 are in Area 1 (a common area, also known as a standard or regular area).

R2 is an Area Border Router (ABR) because it connects Area 0 and Area 1. ABRs are responsible for summarizing and advertising routes between areas.

What is a Common Area in OSPFv3?:

A "common area" in OSPFv3 refers to a standard or regular OSPF area, as opposed to special areas like Stub, Totally Stubby, Not-So-Stubby Area (NSSA), or Totally NSSA. Common areas allow all types of LSAs, including inter-area, intra-area, and external LSAs, to be flooded within the area, except for restrictions in special area types.

Since Area 1 is described as a "common area," it behaves like a standard OSPF area, allowing the full exchange of LSAs, including Inter-Area-Prefix-LSAs.

Role of Inter-Area-Prefix-LSA (Type 3 LSA in OSPFv3):

Inter-Area-Prefix-LSAs (Type 3 LSAs in OSPFv3) are used by ABRs to advertise prefixes from one area to another. These LSAs are critical for inter-area routing, allowing routers in one area to learn about networks in other areas.

In this case, R2, as an ABR, generates Inter-Area-Prefix-LSAs to describe routes (network segments) in Area 1 and advertises them into Area 0. Conversely, R2 also receives Inter-Area-Prefix-LSAs from Area 0 (via R1) and advertises them into Area 1.

Does the Inter-Area-Prefix-LSA Exist in Both Area 0 and Area 1?:

Yes, Inter-Area-Prefix-LSAs exist in both areas because R2, as an ABR, floods these LSAs into both Area 0 and Area 1. Specifically:

R2 generates Inter-Area-Prefix-LSAs for network segments in Area 1 and advertises them into Area 0, where R1 (in Area 0) can receive and process them.

Similarly, R2 receives Inter-Area-Prefix-LSAs for network segments in Area 0 (from R1) and advertises them into Area 1, where R3 (in Area 1) can receive and process them.

Since Area 1 is a common area (not a stub or NSSA), it allows Inter-Area-Prefix-LSAs to be flooded within the area, ensuring that routers like R3 can learn about routes in Area 0, and routers like R1 can learn about routes in Area 1.

Verifying the Statement:

The statement claims that R2 generates an Inter-Area-Prefix-LSA to describe the routes of a network segment in Area 1, and such an LSA exists in both Area 0 and Area 1. This is accurate because:

R2, as an ABR, generates Inter-Area-Prefix-LSAs for Area 1’s network segments and floods them into Area 0.

R2 also receives and floods Inter-Area-Prefix-LSAs from Area 0 into Area 1.

Therefore, Inter-Area-Prefix-LSAs describing routes in Area 1 exist in both Area 0 and Area 1, making the statement true.

Conclusion:

The statement is true because Inter-Area-Prefix-LSAs generated by R2 for Area 1’s network segments are flooded into both Area 0 and Area 1, and Area 1, being a common area, allows these LSAs to exist within it.

References to HCIP-Datacom-Advanced Routing & Switching Technology Documents:

HCIP-Datacom-Advanced Routing & Switching Technology V1.0, Section on OSPFv3: OSPF Area Types, Inter-Area Routing, and LSA Types (specifically Inter-Area-Prefix-LSA, Type 3 LSA).

HCIP-Datacom-Advanced Routing & Switching Technology V1.0, Chapter on OSPF Routing Protocols: ABR Behavior, Common Areas, and LSA Flooding Mechanisms.

Comprehensive and Detailed In-Depth Explanation:

Understanding the IS-IS Levels and Default Route Advertisement:

R1 is a Level-1 router

R2 is a Level-1-2 router (meaning it connects both Level-1 and Level-2 areas)

R3 is a Level-2-only router

Step 1: What Does "default-route-advertise always level-1" Do?

This command forces R1 to advertise a default route (0.0.0.0/0) to all its Level-1 IS-IS neighbors, regardless of whether R1 has a default route in its routing table.

Since R1 is a Level-1 router, it does not participate in Level-2 routing, meaning it relies on R2 (a Level-1-2 router) for external connectivity.

Step 2: Checking the Routing Tables

R1: Since it is only a Level-1 router and does not receive a default route from any higher-level router, it does not have a default route in its own routing table. ✅ (D is correct)

R2: Since R1 advertises the default route at Level-1, R2 (a Level-1-2 router) receives this default route in its Level-1 database. ✅ (B is correct)

R3: R3 is a Level-2-only router, and default routes are not automatically leaked between Level-1 and Level-2 unless explicitly configured.

Since no explicit route leaking configuration is mentioned, R3 will not have the default route ❌ (C is incorrect).

A is incorrect because the command successfully advertises a default route from R1 to Level-1 neighbors like R2.

Final Answer: ✅ B, D

References:

HCIP-Datacom-Advanced Routing & Switching Technology V1.0 – IS-IS Default Route Advertisement

IS-IS Routing Level-1 and Level-2 Behavior

IS-IS Route Leaking and Default Route Propagation