Huawei Updated H12-831_V1.0 Exam Questions and Answers by thiago

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:

1. Understanding the Routing Issue

R1 and R4 are BGP routers and have an IBGP connection.

R2 and R3 are OSPF-only routers (they do not run BGP).

Networks 10.1.1.0/24 and 10.4.4.0/24 are advertised into BGP but not OSPF.

PC1 (10.1.1.1) and PC2 (10.4.4.1) need communication, but their networks are not known to OSPF routers R2 and R3.

To fix this, we need a method that ensures R2 and R3 learn the routes for 10.1.1.0/24 and 10.4.4.0/24.

2. Evaluating Each Answer Option

Option A: "Deploy policy-based routing on R1 and specify R2 as the next hop for traffic from PC1 to PC2."

Incorrect.

Policy-Based Routing (PBR) does not solve the issue of missing routes in OSPF.

Even if R1 forwards traffic to R2, R2 does not know how to reach 10.4.4.0/24, causing packet drops.

A proper routing protocol solution is required instead of PBR.

Option B: "Deploy MPLS and LDP on R1 to R4 and establish LSPs for routes 1.1.1.1/32 and 4.4.4.4/32."

Incorrect.

MPLS requires label-switched paths (LSPs) but does not distribute routing information itself.

The real problem is that R2 and R3 do not have routing entries for 10.1.1.0/24 and 10.4.4.0/24.

MPLS does not fix the missing route advertisement issue.

Option C: "Run BGP on R2 and R3, and establish full-mesh IBGP connections in AS 123."

Correct.

If R2 and R3 run BGP, they can form IBGP sessions with R1 and R4 and learn routes 10.1.1.0/24 and 10.4.4.0/24 via BGP.

R2 and R3 would then be able to forward traffic correctly between PC1 and PC2.

This is a valid method to fix the issue.

Option D: "On R1 and R4, import routes 10.1.1.0/24 and 10.4.4.0/24 into OSPF."

Correct.

By redistributing BGP routes into OSPF, R1 and R4 can ensure that R2 and R3 learn the missing networks (10.1.1.0/24 and 10.4.4.0/24) via OSPF.

This allows full reachability without running BGP on R2 and R3.

This is another valid method to fix the issue.

Final Answer:

✅ C and D are correct.

HCIP-Datacom-Advanced Routing & Switching Technology References:

BGP and OSPF Route Redistribution

IBGP Full-Mesh Requirement and Route Propagation

How Policy-Based Routing Works and Its Limitations