mediumMultiple Choice
350-401 Practice Question: Given the following configuration: interface…
Given the following configuration:
interface GigabitEthernet0/0 ip address 10.1.1.1 255.255.255.0 ip pim sparse-mode ip igmp version 3
What is the purpose of the 'ip igmp version 3' command?
⚠ Common exam trap
Cisco often tests the misconception that IGMPv3 is simply a 'newer version' with generic improvements, when in fact its key differentiator is source-specific filtering for SSM support.
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
✓
It enables IGMP version 3, which allows hosts to join multicast groups from specific sources, supporting SSM.
The 'ip igmp version 3' command enables IGMPv3 on the interface, which supports Source-Specific Multicast (SSM) by allowing hosts to specify both the multicast group and the source address in their membership reports. This is essential for SSM operation with PIM sparse-mode, as IGMPv3 provides the source filtering capability that IGMPv2 lacks.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
It enables IGMP version 3, which allows hosts to join multicast groups from specific sources, supporting SSM.
Why this is correct
IGMPv3 introduces source-specific membership (INCLUDE/EXCLUDE) messages, allowing hosts to explicitly request traffic from a particular source (S,G). This is the foundation of SSM, where the recipient signals a join for a specific source and group, and the router can then forward multicast traffic exclusively from that source. Without IGMPv3, SSM cannot function because legacy IGMPv1/v2 reports are group-only and lack source selection.
- ✗
It enables IGMP version 3, which increases the number of multicast groups supported to 1024.
Why it's wrong here
The IGMP protocol version does not impose a numeric limit on the number of multicast groups a router can support. Group capacity is governed by hardware tables, available memory, and the specific platform design, not by the IGMP protocol. IGMPv3 does not add or change any such limit, so the statement incorrectly conflates a protocol feature with a platform-dependent scalability parameter.
- ✗
It enables IGMP version 3, which is required for PIM dense-mode operation.
Why it's wrong here
PIM dense-mode (PIM-DM) relies on flood-and-prune behavior and only needs IGMPv2 (or even IGMPv1 on some legacy network) to learn group membership on directly connected segments. IGMPv3 is not a prerequisite for PIM-DM; it is primarily beneficial for sparse-mode SSM operation. The requirement for IGMPv3 arises when source-filtering is needed, not for dense-mode forwarding logic.
- ✗
It enables IGMP version 3, which disables IGMP snooping on the interface.
Why it's wrong here
IGMP snooping is an independent Layer 2 optimization that inspects IGMP messages on a switch to build bridge forwarding tables and restrict multicast frames to interested ports. Enabling IGMPv3 on a router interface does not automatically disable snooping; in fact, snooping must be IGMPv3-aware to correctly parse v3 membership reports and source-specific entries. The two features operate at different layers and do not have a cause-effect disabling relationship.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.