H12-831_V1.0 Exam Dumps : HCIP-Datacom-Advanced Routing & Switching Technology V1.0

Comprehensive and Detailed In-Depth Explanation:

Step 1: Analyzing the Primary Path

The given network uses IS-IS Auto FRR, which ensures a backup route in case of failure.

The shortest path from R1 to 10.0.3.3/32 is calculated based on the OSPF link costs:

Path 1 (Primary Path): R1 → R2 → R3

Cost: 10 (R1→R2) + 5 (R2→R3) = 15 ✅

Step 2: Checking the Backup Path

The statement claims that the backup path is R1 → R4 → R2 → R3. Let's calculate the cost:

Path 2 (Backup Path via R4): R1 → R4 → R2 → R3

Cost: 10 (R1→R4) + 50 (R4→R2) + 5 (R2→R3) = 65 ❌ (Too high)

The backup path should be an alternative shortest path that is as close as possible to the primary path in cost.

R1 → R4 → R2 → R3 is not a feasible backup path because the cost (65) is significantly higher than the primary path (15).

Step 3: Correct Backup Path Selection

If IS-IS Auto FRR is enabled, a feasible backup path should have a cost close to the primary path.

In this scenario, no viable alternative path meets the Auto FRR requirements efficiently.

The given backup path is incorrect.

Final Answer: ✅ FALSE (Option B)

References:

HCIP-Datacom-Advanced Routing & Switching Technology V1.0 – IS-IS Auto FRR Mechanism

OSPF Route Selection and Fast Reroute Principles

OSPF and IS-IS Path Cost Calculation

Comprehensive and Detailed In-Depth Explanation:

Step 1: Identify the Primary Path

The shortest OSPF cost to 10.0.3.3/32 from R1 is through R5:

R1 → R5 (Cost 10) → R3 (Cost 10) = Total Cost 20

The primary outbound interface from R1 to R5 is GE0/0/1.

Step 2: Identify the Backup Path (OSPF IP FRR & ECMP)

OSPF IP Fast Reroute (FRR) provides a backup next-hop in case the primary link (R1 → R5) fails.

A feasible backup path must have a cost equal to or close to the primary path, but it must avoid the same failure point.

Alternative Path Calculation:

Path 1 (R1 → R2 → R3)

R1 → R2 (Cost 10), R2 → R3 (Cost 10) → Total Cost = 20 ✅

Uses interface GE0/0/2 on R1.

Path 2 (R1 → R4 → R3)

R1 → R4 (Cost 10), R4 → R3 (Cost 10) → Total Cost = 20 ✅

Uses interface GE0/0/3 on R1.

Final Decision on the Backup Interface

Since both paths R1 → R2 → R3 and R1 → R4 → R3 have equal costs, either can be used for backup.

However, R1 → R2 → R3 shares a direct cost path with R5, meaning it may not be preferred as a full FRR backup.

The best backup outbound interface in this scenario is GE0/0/3 (R1 → R4 → R3).

Final Answer: ✅ C (GE0/0/3)

References:

HCIP-Datacom-Advanced Routing & Switching Technology V1.0 – OSPF IP FRR (Fast Reroute) Mechanism

OSPF Equal-Cost Multi-Path (ECMP) and Backup Route Selection

OSPF Route Calculation and Best-Path Selection

Comprehensive and Detailed In-Depth Explanation:

To determine the correct configuration, we need to analyze how MPLS LDP (Label Distribution Protocol) is correctly enabled on a Huawei router.

1. Required Steps to Enable MPLS LDP on R1

To enable MPLS LDP on R1 and establish LDP sessions, the following steps must be followed:

✅ Step 1: Configure the MPLS LSR ID (Loopback IP recommended)

MPLS LSR ID is a unique identifier for the Label Switch Router (LSR).

Command:

shell

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mpls lsr-id 1.1.1.1

Why?

The LSR ID must be configured for LDP to function properly in an MPLS network.

It is usually set to a loopback address for stability and consistency.

✅ Step 2: Enable MPLS Globally

Command:

shell

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mpls

Why?

This enables MPLS forwarding on the device.

✅ Step 3: Enable MPLS LDP Globally

Command:

shell

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mpls ldp

Why?

LDP is needed for label distribution in the MPLS domain.

Without this, routers cannot exchange MPLS labels.

✅ Step 4: Enable MPLS and LDP on the Required Interface

Command:

shell

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interface gigabitethernet 0/0/1

mpls

mpls ldp

Why?

MPLS must be enabled on interfaces that participate in MPLS forwarding.

LDP must also be enabled on these interfaces to distribute labels over MPLS links.

2. Analyzing the Answer Choices

✅ Option B (Correct)

shell

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[R1] mpls lsr-id 1.1.1.1 ✅ (Sets LSR ID)

[R1] mpls ✅ (Enables MPLS globally)

[R1-mpls] quit

[R1] mpls ldp ✅ (Enables LDP globally)

[R1-mpls-ldp] quit

[R1] interface gigabitethernet 0/0/1

[R1-GigabitEthernet0/0/1] mpls ✅ (Enables MPLS on interface)

[R1-GigabitEthernet0/0/1] mpls ldp ✅ (Enables LDP on interface)

[R1-GigabitEthernet0/0/1] quit

This configuration correctly enables MPLS LDP on R1.

All required steps are followed, including the LSR ID, MPLS, LDP, and interface activation.

❌ Option A (Incorrect)

shell

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[R1] mpls lsr-id 1.1.1.1

[R1] mpls

[R1-mpls] quit

[R1] mpls ldp

[R1-mpls-ldp] quit

[R1] interface gigabitethernet 0/0/1

[R1-GigabitEthernet0/0/1] mpls ✅

[R1-GigabitEthernet0/0/1] quit ❌ (Missing "mpls ldp" under interface)

Missing mpls ldp under interface configuration.

Without this, the interface will not establish an LDP session → Incorrect.

❌ Option C (Incorrect)

shell

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[R1] mpls

[R1-mpls] quit

[R1] mpls ldp

[R1-mpls-ldp] quit

[R1] interface gigabitethernet 0/0/1

[R1-GigabitEthernet0/0/1] mpls

[R1-GigabitEthernet0/0/1] mpls ldp

[R1-GigabitEthernet0/0/1] quit

Missing mpls lsr-id 1.1.1.1.

LSR ID is critical for LDP sessions → Incorrect.

❌ Option D (Incorrect)

shell

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[R1] mpls lsr-id 1.1.1.1

[R1] mpls

[R1-mpls] quit

[R1] interface gigabitethernet 0/0/1

[R1-GigabitEthernet0/0/1] mpls

[R1-GigabitEthernet0/0/1] mpls ldp

[R1-GigabitEthernet0/0/1] quit

Missing global MPLS LDP configuration (mpls ldp).

Without enabling LDP globally, labels will not be distributed.

This makes LDP sessions fail. → Incorrect.