Comprehensive and Detailed In-Depth Explanation:
1. Understanding SR-MPLS (Segment Routing with MPLS):
Segment Routing (SR)leverages MPLS labels to define paths through the network.
The labels representsegments(nodes or specific paths) rather than traditional LDP or RSVP-TE labels.
Thelabel stackdetermines the forwarding path through the network.
Top Label:Determines thenext hop.
Next Label:After label pop, it indicates thesubsequent hop.
2. Analyzing the Given Label Stack:
The label stack encapsulated byR1is as follows:
Layer2:2046
2013
2032
2024
2046
Layer3
Thetop label (2046)indicates that thenext-hop routerisR4.
AfterR4pops the top label, thenext label (2046)directs the packet toR6.
3. Forwarding Path Analysis:
Step 1:R1sends the packet toR2based on internal routing.
Step 2:R2forwards the packet directly toR4as dictated by the top label (2046).
Step 3:R4pops the top label (2046) and checks the next label (again2046), directing the packet toR6.
Step 4:R6receives the packet as the final destination.
4. Why Option B is Correct:
The pathR1-R2-R4-R6matches thelabel stack processingin SR-MPLS.
Thelabels indicate the shortest pathchosen by SR policies, which isR1 → R2 → R4 → R6.
TheSR-MPLS label stackefficiently 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 thelabel sequenceas the labels clearly indicate adirect path via R4, not throughR3 and R5.
Option C (R1-R3-R2-R4-R6):
This path is longer and unnecessary, as thelabel stackindicates a moredirect path via R2 and R4.
[References:, 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, , , , , ]
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