IGMP report suppression
Multicast routers periodically send a membership query message (every 60 seconds) to check which hosts are still interested in receiving a specific multicast group. Hosts have to respond with a membership report message.
Each host select a random report delay time to ensure not all hosts send the same reply at the same time. The maximum response time is defined in the IGMP membership query:
IGMP membership query max response time
When the timer expires, the host will send the membership report but only if it doesn’t hear a report from another host. This is called report suppression.
Keep in mind that IGMP snooping prevents report suppression:
IGMP snooping prevents report suppression
This means that on modern networks, all hosts send a membership report.
SW1#show ip igmp snooping vlan 100 Global IGMP Snooping configuration: ------------------------------------------- IGMP snooping : Enabled Global PIM Snooping : Disabled IGMPv3 snooping : Enabled Report suppression : Enabled TCN solicit query : Disabled TCN flood query count : 2 Robustness variable : 2 Last member query count : 2 Last member query interval : 1000 Vlan 100: -------- IGMP snooping : Enabled Pim Snooping : Disabled IGMPv2 immediate leave : Disabled Explicit host tracking : Enabled Multicast router learning mode : pim-dvmrp CGMP interoperability mode : IGMP_ONLY Robustness variable : 2 Last member query count : 2 Last member query interval : 1000
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