350-501 MPLS and Segment Routing Practice Question
An engineer is deploying MPLS in the core and wants to ensure that all core routers use the same label for a specific prefix, regardless of which router originated it. Which MPLS label allocation mode should be used?
⚠ Common exam trap
Cisco often tests the distinction between per-prefix and per-next-hop label modes, and the trap here is that candidates confuse per-next-hop (which creates multiple labels for the same prefix) with per-prefix, thinking that per-next-hop ensures consistency when it actually does the opposite.
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
✓
Per-prefix label mode
Per-prefix label mode (option C) is correct because it assigns a single label for a specific prefix across all core routers, regardless of which router originated the route. This ensures label consistency, which is critical for proper MPLS forwarding and troubleshooting. In contrast, per-next-hop or per-interface modes would create different labels for the same prefix based on the next hop or interface, breaking the requirement for uniform label allocation.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Per-interface label mode
Why it's wrong here
Per-interface assigns a different label for each interface, not consistent across routers.
- ✗
Per-next-hop label mode
Why it's wrong here
Per-next-hop assigns labels based on next hop, not per prefix.
- ✓
Per-prefix label mode
Why this is correct
Per-prefix allocates one label per prefix, ensuring same label across all routers.
- ✗
Per-VRF label mode
Why it's wrong here
Per-VRF is for VPNs, not for core prefix labels.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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