350-501 Architecture Practice Question
An SP is migrating its core network to Segment Routing (SR-MPLS). The network uses IS-IS as the IGP with SR extensions. Which three statements about SR-MPLS architecture are correct?
⚠ Common exam trap
Cisco often tests the misconception that the SRGB must be identical across all routers, when in reality only the mapping from prefix SID to label must be consistent, and the SRGB can vary as long as the label space is properly coordinated.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Adjacency SIDs are local to a router and indicate a specific link.
An Adjacency SID is a local label assigned to a specific IS-IS adjacency, representing a particular link between two routers. It is locally significant and used to steer traffic over that specific next-hop, not globally unique.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The OSPF protocol cannot be used for SR-MPLS because it does not support SR extensions.
Why it's wrong here
Incorrect. OSPF has SR extensions (OSPFv2 SR) and can be used for SR-MPLS.
- ✓
Adjacency SIDs are local to a router and indicate a specific link.
Why this is correct
Correct. Adjacency SIDs are locally significant and represent a specific interface or link.
- ✓
A prefix SID is a global label that identifies a specific prefix in the network.
Why this is correct
Correct. Prefix SIDs are global and identify a prefix or node.
- ✗
The SRGB must be identical across all routers in the domain to ensure global uniqueness.
Why it's wrong here
Incorrect. While recommended, the SRGB can differ; prefix SIDs must be globally unique but the block itself can vary.
- ✓
Segment IDs (SIDs) are allocated from the SRGB (Segment Routing Global Block) and advertised via IS-IS.
Why this is correct
Correct. SIDs are allocated from SRGB and distributed via IS-IS.
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