Quick Answer
The answer is mLDP, or Multipoint Label Distribution Protocol, because it is the specific mechanism designed to dynamically establish multicast label-switched paths across an MPLS core for Layer 3 VPNs. Unlike PIM-SM or PIM-DM, which operate at the IP routing level and are used for building multicast trees between customer sites, mLDP works within the MPLS data plane to distribute multicast labels between Provider Edge routers, enabling efficient point-to-multipoint transport without requiring a core routing protocol like PIM. On the Cisco SPCOR 350-501 exam, this question tests your understanding of how service providers separate the core transport from customer multicast signaling—a common trap is confusing the customer-facing PIM modes with the core label distribution mechanism. Remember that mLDP is the core’s “label plumber” for multicast, while PIM is only used on the PE-CE links. A helpful memory tip: “mLDP maps multicast in the MPLS core, PIM is for the customer’s door.”
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 deploying multicast over MPLS L3VPN. Which mechanism is used to provide multicast in the core between PE routers?
IGMP
Why wrong: IGMP is for host membership, not core multicast.
PIM-SM
Why wrong: PIM-SM can be used in the core but mLDP is the standard for MPLS multicast.
PIM-DM
Why wrong: PIM-DM is dense mode, not typically used in MPLS core.
mLDP
mLDP is the multicast label distribution protocol for MPLS.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
mLDP
mLDP is used for multicast label distribution in the MPLS core. PIM-SM and PIM-DM are protocol independent multicast modes, but not specifically for MPLS core multicast. IGMP is for host registration.
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.
IGMP
Why it's wrong here
IGMP is for host membership, not core multicast.
PIM-SM
Why it's wrong here
PIM-SM can be used in the core but mLDP is the standard for MPLS multicast.
PIM-DM
Why it's wrong here
PIM-DM is dense mode, not typically used in MPLS core.
mLDP
Why this is correct
mLDP is the multicast label distribution protocol for MPLS.
Related concept
Read the scenario before looking for a memorised answer.
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.
Architecture — study guide chapter
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FAQ
Architecture — This question tests Architecture — Read the scenario before looking for a memorised answer..
The correct answer is: mLDP — mLDP is used for multicast label distribution in the MPLS core. PIM-SM and PIM-DM are protocol independent multicast modes, but not specifically for MPLS core multicast. IGMP is for host registration.
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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