- A
IGMP snooping reduces unnecessary multicast flooding on a Layer 2 switch.
Correct because IGMP snooping allows the switch to forward multicast frames only to ports that have joined the group, reducing flooding.
- B
IGMP snooping uses the IGMP querier election process to select the switch with the highest IP address as the querier.
Why wrong: Incorrect because the IGMP querier is elected based on the lowest IP address, not the highest.
- C
IGMP snooping can be configured to replace IGMP on the router interface.
Why wrong: Incorrect because IGMP snooping is a Layer 2 feature that works alongside IGMP; it does not replace the IGMP protocol on routers.
- D
IGMP snooping listens to IGMP membership reports and leave messages to build a forwarding table.
Correct because the switch examines IGMP messages to learn which ports have joined or left a multicast group.
- E
IGMP snooping modifies the IP header of multicast packets to include group membership information.
Why wrong: Incorrect because IGMP snooping does not modify packets; it only inspects IGMP control messages to update its forwarding database.
Quick Answer
The answer is that IGMP snooping listens to IGMP membership reports and leave messages to build a forwarding table. This is correct because IGMP snooping operates as a Layer 2 switch feature that passively intercepts IGMP traffic between hosts and routers, allowing the switch to learn which ports have active multicast receivers. By tracking these reports and leave messages, the switch constructs a forwarding table that constrains multicast traffic to only those ports, preventing unnecessary flooding to all ports. On the ENCOR 350-401 exam, this concept tests your understanding of how switches optimize multicast delivery without modifying IP headers or replacing IGMP itself—a common trap is confusing IGMP snooping with the querier election process, which actually selects the lowest IP address, not the highest. Remember the memory tip: snooping is about listening, not talking; it builds a table by watching reports and leaves.
CCNP IP Multicast Practice Question
This 350-401 practice question tests your understanding of ip multicast. 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.
Which two statements about IGMP snooping are true? (Choose two.)
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
IGMP snooping reduces unnecessary multicast flooding on a Layer 2 switch.
IGMP snooping operates on Layer 2 switches to constrain multicast traffic to only those ports that have interested receivers. It listens to IGMP messages between hosts and routers to build a forwarding table. It does not replace IGMP; it is complementary. The querier is elected based on the lowest IP address, not the highest. IGMP snooping does not modify IP multicast headers.
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.
- ✓
IGMP snooping reduces unnecessary multicast flooding on a Layer 2 switch.
Why this is correct
Correct because IGMP snooping allows the switch to forward multicast frames only to ports that have joined the group, reducing flooding.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
IGMP snooping uses the IGMP querier election process to select the switch with the highest IP address as the querier.
Why it's wrong here
Incorrect because the IGMP querier is elected based on the lowest IP address, not the highest.
- ✗
IGMP snooping can be configured to replace IGMP on the router interface.
Why it's wrong here
Incorrect because IGMP snooping is a Layer 2 feature that works alongside IGMP; it does not replace the IGMP protocol on routers.
- ✓
IGMP snooping listens to IGMP membership reports and leave messages to build a forwarding table.
Why this is correct
Correct because the switch examines IGMP messages to learn which ports have joined or left a multicast group.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
IGMP snooping modifies the IP header of multicast packets to include group membership information.
Why it's wrong here
Incorrect because IGMP snooping does not modify packets; it only inspects IGMP control messages to update its forwarding database.
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 350-401 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 350-401 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 350-401 question test?
IP Multicast — This question tests IP Multicast — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: IGMP snooping reduces unnecessary multicast flooding on a Layer 2 switch. — IGMP snooping operates on Layer 2 switches to constrain multicast traffic to only those ports that have interested receivers. It listens to IGMP messages between hosts and routers to build a forwarding table. It does not replace IGMP; it is complementary. The querier is elected based on the lowest IP address, not the highest. IGMP snooping does not modify IP multicast headers.
What should I do if I get this 350-401 question wrong?
Identify which 350-401 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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Same concept, more angles
1 more ways this is tested on 350-401
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Which three statements about IGMP snooping are true? (Choose three.)
medium- ✓ A.IGMP snooping reduces multicast flooding on a VLAN by forwarding traffic only to ports that have joined the group.
- ✓ B.IGMP snooping builds a Layer 2 forwarding table that maps multicast MAC addresses to switch ports.
- ✓ C.IGMP snooping forwards IGMP membership reports only toward the multicast router (querier).
- D.IGMP snooping suppresses all IGMP general queries from the multicast router.
- E.IGMP snooping requires PIM to be enabled on the switch.
Why A: IGMP snooping optimizes multicast forwarding at Layer 2 by monitoring IGMP messages. It builds a snooping table, forwards reports only to the querier, and can be configured with static entries. It does not suppress queries or require PIM.
Last reviewed: Jun 18, 2026
This 350-401 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 350-401 exam.
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