300-510 · Question #285
Which fact must a network architect consider when implementing IGMP in a multicast routing environment?
The correct answer is A. If SSM is in use IGMPv3 must be enabled. SSM (Source-Specific Multicast) requires IGMPv3 because only IGMPv3 supports source-specific membership reports that allow hosts to specify the multicast source address alongside the group.
Question
Which fact must a network architect consider when implementing IGMP in a multicast routing environment?
Options
- AIf SSM is in use IGMPv3 must be enabled
- BIf BISS support is required IGMPv2 must be enabled
- CIf leave latency is critical IGMPv3 must be enabled
- DIf PIM-DM is required, IGMPv2 must be enabled
How the community answered
(20 responses)- A95% (19)
- D5% (1)
Why each option
SSM (Source-Specific Multicast) requires IGMPv3 because only IGMPv3 supports source-specific membership reports that allow hosts to specify the multicast source address alongside the group.
SSM relies on (S,G) channel subscriptions where hosts must report both the group and the specific source address. Only IGMPv3 supports INCLUDE mode with source lists, which is the mechanism hosts use to join SSM channels. IGMPv1 and IGMPv2 only carry (*,G) group memberships and cannot encode source-specific information, making them incompatible with SSM.
BISS is not a recognized standard multicast feature that maps to a specific IGMP version requirement, making this pairing technically inaccurate.
Leave latency improvements were introduced by IGMPv2 via the Leave Group message and group-specific queries, not IGMPv3, so IGMPv3 is not required solely for reducing leave latency.
PIM-DM (Dense Mode) operates independently of IGMP version and has no specific requirement for IGMPv2 to function correctly.
Concept tested: IGMPv3 requirement for Source-Specific Multicast
Source: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipmulti_igmp/configuration/xe-16/imc-igmp-xe-16-book/imc-igmp-v3.html
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