352-001 · Question #734
In a multicast switched LAN with IGMP snooping enabled. Users report that they often receive all multicast groups for brief periods of time (traffic a flooded everywhere). You must improve the…
The correct answer is D. IGMPv3 Explicit Host Tracking. Brief multicast flooding in an IGMP snooping environment typically occurs when membership state expires and the switch must flood while waiting for new reports. IGMPv3 Explicit Host Tracking eliminates this gap by maintaining per-host membership records.
Question
In a multicast switched LAN with IGMP snooping enabled. Users report that they often receive all multicast groups for brief periods of time (traffic a flooded everywhere). You must improve the design of the network and address the issue. Which feature do you consider to stop this frequent multicast flooding from occurring?
Options
- AVTP VLAN pruning
- BSTP PortFast
- CPIM-SSM Mapping
- DIGMPv3 Explicit Host Tracking
How the community answered
(41 responses)- A17% (7)
- B7% (3)
- C5% (2)
- D71% (29)
Why each option
Brief multicast flooding in an IGMP snooping environment typically occurs when membership state expires and the switch must flood while waiting for new reports. IGMPv3 Explicit Host Tracking eliminates this gap by maintaining per-host membership records.
VTP VLAN pruning restricts the propagation of VLAN traffic across trunk links and has no effect on multicast flooding caused by gaps in the IGMP snooping membership table.
STP PortFast bypasses Listening and Learning STP states on access ports and is entirely unrelated to multicast group membership tracking or IGMP snooping behavior.
PIM-SSM Mapping translates IGMPv1/v2 group memberships to Source-Specific Multicast groups at the router level and does not prevent Layer 2 flooding caused by expired membership state in the switch's IGMP snooping table.
IGMPv3 Explicit Host Tracking allows the switch to record exactly which individual hosts are subscribed to each multicast group, so when a query is issued or a leave is received, the switch immediately knows whether any remaining hosts still need the stream without waiting for membership report responses. This eliminates the flooding window that arises when the switch loses group membership state and must re-learn it, directly stopping the intermittent flooding behavior described.
Concept tested: IGMPv3 Explicit Host Tracking to prevent IGMP snooping flooding
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-expl-track.html
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