Huawei H12-891_V1.0 Exam - Topic 2 Question 90 Discussion

Comprehensive and Detailed In-Depth

1. Understanding SR-MPLS (Segment Routing with MPLS):

Segment Routing (SR) leverages MPLS labels to define paths through the network.

The labels represent segments (nodes or specific paths) rather than traditional LDP or RSVP-TE labels.

The label stack determines the forwarding path through the network.

Top Label: Determines the next hop.

Next Label: After label pop, it indicates the subsequent hop.

2. Analyzing the Given Label Stack:

The label stack encapsulated by R1 is as follows:

Layer2: 2046

2013

2032

2024

2046

Layer3

The top label (2046) indicates that the next-hop router is R4.

After R4 pops the top label, the next label (2046) directs the packet to R6.

3. Forwarding Path Analysis:

Step 1: R1 sends the packet to R2 based on internal routing.

Step 2: R2 forwards the packet directly to R4 as dictated by the top label (2046).

Step 3: R4 pops the top label (2046) and checks the next label (again 2046), directing the packet to R6.

Step 4: R6 receives the packet as the final destination.

4. Why Option B is Correct:

The path R1-R2-R4-R6 matches the label stack processing in SR-MPLS.

The labels indicate the shortest path chosen by SR policies, which is R1 R2 R4 R6.

The SR-MPLS label stack efficiently guides the packet through the optimal path without complex signaling.

Why Other Options Are Incorrect:

Option A (R1-R2-R3-R5-R6):

This path does not match the label sequence as the labels clearly indicate a direct path via R4, not through R3 and R5.

Option C (R1-R3-R2-R4-R6):

This path is longer and unnecessary, as the label stack indicates a more direct path via R2 and R4.

Huawei HCIE-Datacom V1.0 Training Materials

Huawei Official Documentation: SR-MPLS Configuration Guide

RFC 8660 - Segment Routing with MPLS Data Plane

HCIE-Datacom Knowledge Base: Segment Routing and MPLS