The answer is that ASBRs exchange VPNv4 routes directly via MP-EBGP, which is the unique design characteristic of Inter-AS MPLS VPN Option B compared to Option A. This is correct because Option B eliminates the need for VRF configurations on the ASBRs; instead, the ASBRs maintain a single VPNv4 routing table and use Multiprotocol-EBGP to exchange labeled VPNv4 prefixes directly between autonomous systems, preserving end-to-end MPLS labels. In contrast, Option A requires VRF-to-VRF handoffs at the ASBR, which breaks the MPLS label path and forces IP forwarding. On the Cisco SPCOR 350-501 exam, this concept tests your understanding of inter-AS scalability and label preservation, often appearing as a comparison question where the trap is confusing Option B’s direct VPNv4 exchange with Option A’s VRF-based approach. A common memory tip is: “Option B is the ‘Bare’ exchange—no VRF, just VPNv4 between ASBRs.”
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.
An SP is deploying Inter-AS MPLS VPN option B. Which design characteristic is unique to Option B compared to Option A?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
ASBRs exchange VPNv4 routes directly via MP-EBGP
Option B uses VPNv4 exchange between ASBRs without VRF, while Option A uses VRF-to-VRF. Option D is correct. Option A is wrong because Option B does not require VRF on ASBR. Option B is wrong because MPLS is required. Option C is wrong because full mesh is not required in Option B.
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.
✓
ASBRs exchange VPNv4 routes directly via MP-EBGP
Why this is correct
Option B uses MP-EBGP between ASBRs to exchange VPNv4 routes.
Related concept
Read the scenario before looking for a memorised answer.
✗
Requires a full mesh of MP-IBGP sessions between all PEs
Why it's wrong here
Option A does not require full mesh, Option B uses EBGP between ASBRs.
✗
ASBRs maintain separate VRF for each VPN
Why it's wrong here
Option B does not require VRF on ASBRs.
✗
Traffic is forwarded using IP, not MPLS
Why it's wrong here
Option B uses MPLS labels between ASBRs.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→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 350-501 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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: ASBRs exchange VPNv4 routes directly via MP-EBGP — Option B uses VPNv4 exchange between ASBRs without VRF, while Option A uses VRF-to-VRF. Option D is correct. Option A is wrong because Option B does not require VRF on ASBR. Option B is wrong because MPLS is required. Option C is wrong because full mesh is not required in Option B.
What should I do if I get this 350-501 question wrong?
Identify which 350-501 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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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