In OSPF-based SR-MPLS TE, Adjacency Segment Identifiers (Adj-SIDs) are locally assigned by each router for its directly connected interfaces. These labels are allocated from the Segment Routing Local Block (SRLB) configured on the router. By default, Huawei routers use an SRLB range starting at 9000, and Adj-SIDs are assigned sequentially (e.g., 9000, 9001, 9002, etc.) to each adjacency.
For P3, adjacency labels correspond to its outgoing interfaces. Assuming P3 has two adjacencies (e.g., to P2 and P4, as inferred from typical network topologies), it will allocate two unique Adj-SIDs from its SRLB. Based on Huawei’s implementation:
The first adjacency (e.g., to P2) is assigned the next available label in the SRLB (e.g., 9002).
The second adjacency (e.g., to P4) is assigned the subsequent label (e.g., 9003).
Analysis of Options:
Option B (9002): Likely assigned to P3’s first adjacency (e.g., link to P2).
Option C (9003): Likely assigned to P3’s second adjacency (e.g., link to P4).
Option A (9006) and D (9005): These labels are likely allocated by other routers (e.g., P4 or P5), as they fall outside the sequential range assigned by P3.
Key Points:
Adj-SIDs are local to the router and do not conflict with labels from other nodes.
The sequential allocation depends on the SRLB configuration. If the SRLB starts at 9000, labels 9000 and 9001 may be reserved for other purposes (e.g., node SIDs or reserved blocks), leaving 9002 and 9003 for adjacency labels.
Conclusion: P3 allocates 9002 and 9003 for its two adjacencies. Thus, B and C are correct.
[References:, Huawei HCIE-Datacom Documentation: "OSPFv3 Extensions for Segment Routing" (Section: Adjacency SID Allocation)., Huawei Configuration Guide: "SR-MPLS TE Configuration" (SRLB and Adj-SID Assignment Principles)., Huawei Whitepaper: "Segment Routing Architecture" (Local vs. Global Labels)., , , ]
