- A
The BGP next-hop on the customer carrier's routes must be reachable via IGP in the provider carrier.
For the provider carrier to switch MPLS packets, the BGP next-hop must be reachable via the IGP and have a label binding.
- B
The provider carrier's VRF must have the route-target matching the customer carrier's.
Why wrong: CSC often uses no VRF on the provider carrier; instead, the customer carrier's routes are treated as standard BGP routes.
- C
The provider carrier must be in the same AS as the customer carrier.
Why wrong: Different AS numbers are typical; the provider carrier uses BGP to carry VPN routes.
- D
The customer carrier must use LDP for label distribution.
Why wrong: LDP is used inside the customer carrier network, but the provider carrier does not require LDP from the customer carrier.
Quick Answer
The answer is that the BGP next-hop on the customer carrier’s routes must be reachable via an IGP in the provider carrier. This condition is necessary because in a Carrier Supporting Carrier (CSC) architecture, the provider carrier’s MPLS backbone uses label switching to forward traffic; if the BGP next-hop for the customer carrier’s routes is not reachable through the provider’s IGP, the provider’s edge routers cannot resolve the next-hop to a label-switched path, breaking end-to-end connectivity. On the Cisco SPCOR 350-501 exam, this concept tests your understanding of how CSC separates routing domains while relying on underlying IGP reachability for MPLS transport—a common trap is confusing this with LDP or route-target requirements, which apply to different layers. Remember the memory tip: “Next-hop must be IGP-known in the provider’s zone.”
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.
In a Carrier Supporting Carrier (CSC) architecture, which condition is necessary for the customer carrier's BGP routes to be carried over the provider carrier's MPLS backbone?
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
The BGP next-hop on the customer carrier's routes must be reachable via IGP in the provider carrier.
Option D is correct because in CSC, the customer carrier's BGP next-hop must be reachable via the provider carrier's IGP for label switching to work. Option A is wrong because AS numbers can be different; the provider carrier treats the customer carrier as a VPN. Option B is wrong because LDP is used for label distribution in the customer carrier's network, but it's not a condition for the provider carrier. Option C is wrong because the route-target is used for VPN route import/export, but CSC does not necessarily require a VRF on the provider carrier if using BGP-free core.
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.
- ✓
The BGP next-hop on the customer carrier's routes must be reachable via IGP in the provider carrier.
Why this is correct
For the provider carrier to switch MPLS packets, the BGP next-hop must be reachable via the IGP and have a label binding.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The provider carrier's VRF must have the route-target matching the customer carrier's.
Why it's wrong here
CSC often uses no VRF on the provider carrier; instead, the customer carrier's routes are treated as standard BGP routes.
- ✗
The provider carrier must be in the same AS as the customer carrier.
- ✗
The customer carrier must use LDP for label distribution.
Why it's wrong here
LDP is used inside the customer carrier network, but the provider carrier does not require LDP from the customer carrier.
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.
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FAQ
Questions learners often ask
What does this 350-501 question test?
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: The BGP next-hop on the customer carrier's routes must be reachable via IGP in the provider carrier. — Option D is correct because in CSC, the customer carrier's BGP next-hop must be reachable via the provider carrier's IGP for label switching to work. Option A is wrong because AS numbers can be different; the provider carrier treats the customer carrier as a VPN. Option B is wrong because LDP is used for label distribution in the customer carrier's network, but it's not a condition for the provider carrier. Option C is wrong because the route-target is used for VPN route import/export, but CSC does not necessarily require a VRF on the provider carrier if using BGP-free core.
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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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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