The answer is per-VRF label allocation, which is the correct choice because it assigns a single MPLS label per VRF, allowing all routes within that VRF to share the same label. This directly minimizes the number of labels in the forwarding table compared to per-prefix allocation, while still preserving per-VRF isolation for L3VPN services. On the Cisco SPCOR / CCNP Service Provider Core 350-501 exam, this concept tests your understanding of MPLS label efficiency trade-offs, often appearing in a scenario where the provider must support both L3VPN and L2VPN services without bloating the label table. A common trap is assuming per-prefix allocation is always better for granularity, but the question explicitly asks to minimize labels while maintaining per-VRF allocation—so per-VRF mode is the only fit. Memory tip: think “one label per VRF, not per prefix” to recall that sharing a label across routes reduces the forwarding table size.
350-501 Architecture Practice Question
This 350-501 practice question tests your understanding of architecture. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A service provider is redesigning its MPLS core to support both L3VPN and L2VPN services. They want to minimize the number of labels in the forwarding table while maintaining per-VRF label allocation. Which label allocation mode should be used for the L3VPN service?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "minimum / minimize"
Why it matters: Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Per-VRF label allocation
Per-VRF label allocation assigns a single MPLS label per VRF, meaning all routes within a VRF share the same label. This minimizes the number of labels in the forwarding table compared to per-prefix allocation, while still maintaining per-VRF isolation for L3VPN services. It is the recommended mode when the goal is to reduce label consumption without sacrificing VPN separation.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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-VRF label allocation
Why this is correct
Per-VRF assigns a single label per VRF, minimizing labels while allowing per-VRF forwarding.
Clue confirmation
The clue word "minimum / minimize" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Per-CE label allocation
Why it's wrong here
Per-CE assigns a label per CE router, which is more than per-VRF.
✗
Per-prefix label allocation
Why it's wrong here
Per-prefix assigns a label per route, increasing label table size.
✗
Per-instance label allocation
Why it's wrong here
Per-instance is not a standard MPLS VPN label allocation mode.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between per-VRF and per-prefix label allocation, where candidates mistakenly choose per-prefix because they think it offers finer granularity, but the question explicitly asks for minimizing labels, which per-VRF achieves.
Detailed technical explanation
How to think about this question
In MPLS L3VPN, per-VRF label allocation uses a single label for all routes in a VRF, which is advertised via MP-BGP (RFC 4364). The ingress PE pushes this label, and the egress PE uses it to identify the VRF and perform a lookup on the inner IP header. This mode reduces the BGP table size and label forwarding information base (LFIB) entries, which is critical in large-scale service provider networks with thousands of VRFs.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the 350-501 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Architecture — This question tests Architecture — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Per-VRF label allocation — Per-VRF label allocation assigns a single MPLS label per VRF, meaning all routes within a VRF share the same label. This minimizes the number of labels in the forwarding table compared to per-prefix allocation, while still maintaining per-VRF isolation for L3VPN services. It is the recommended mode when the goal is to reduce label consumption without sacrificing VPN separation.
What should I do if I get this 350-501 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "minimum / minimize". Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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