Quick Answer
The answer is the ASBR routers. In Inter-AS MPLS Option B, directly connected Autonomous System Boundary Routers (ASBRs) exchange labeled VPNv4 prefixes using Multiprotocol Extensions for BGP (MP-eBGP) without requiring a full MPLS Label Switched Path between them, because the physical link itself serves as the LSP. Each ASBR independently allocates a new label for each VPNv4 prefix and advertises it to the neighboring ASBR, enabling seamless end-to-end label switching across different autonomous systems. On the Cisco SPCOR 350-501 exam, this concept tests your understanding of inter-AS label distribution and often appears as a trap where candidates mistakenly think the P routers or Route Reflectors handle the label exchange. A common memory tip is to remember that in Option B, the label is swapped at the border—think “B for Border, B for BGP label swap.”
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.
In Inter-AS MPLS Option B, which routers exchange labeled VPNv4 prefixes directly?
ASBR routers
ASBRs exchange labeled VPNv4 prefixes via MP-eBGP in Option B.
PE routers
Why wrong: PE routers in different AS do not exchange directly; they go through ASBRs.
P routers
Why wrong: P routers do not run BGP.
CE routers
Why wrong: CE routers are customer routers, not part of MPLS VPN signaling.
Route reflectors
Why wrong: Route reflectors are used within an AS, not between ASes.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
ASBR routers
In Option B, ASBRs are directly connected and exchange labeled VPNv4 prefixes via MP-eBGP. They do not require an MPLS LSP between them because they are directly connected. The labels are allocated by each ASBR and advertised to the other.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
ASBR routers
Why this is correct
ASBRs exchange labeled VPNv4 prefixes via MP-eBGP in Option B.
Related concept
Read the scenario before looking for a memorised answer.
PE routers
Why it's wrong here
PE routers in different AS do not exchange directly; they go through ASBRs.
P routers
Why it's wrong here
P routers do not run BGP.
CE routers
Why it's wrong here
CE routers are customer routers, not part of MPLS VPN signaling.
Route reflectors
Why it's wrong here
Route reflectors are used within an AS, not between ASes.
Common exam traps
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
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.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
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.
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FAQ
Architecture — This question tests Architecture — Read the scenario before looking for a memorised answer..
The correct answer is: ASBR routers — In Option B, ASBRs are directly connected and exchange labeled VPNv4 prefixes via MP-eBGP. They do not require an MPLS LSP between them because they are directly connected. The labels are allocated by each ASBR and advertised to the other.
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.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
This 350-501 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 350-501 exam.
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