IGMP Snooping & the Querier Trap

IGMP Snooping is a Layer 2 feature: the switch listens to IGMP Join/Leave traffic and builds a multicast forwarding table so frames go only to ports with interested hosts. Flow Host sends IGMP Membership Report (join) → switch hears it Switch maps multicast MAC → member ports Frames now go to members only; flooding stops […]

Layer 2 Multicast

Switches only know MACs, never IPs — so multicast frames without help flood like broadcast. L2 multicast is therefore about MAC mapping plus IGMP snooping. MAC mapping IPv4 multicast → 0100.5E00.0000–0100.5E7F.FFFF (23 host bits: 3 IP bits collapse per MAC — overlapping groups are expected) IPv6 multicast → 33:33:xx:xx:xx:xx Default switch behaviour: flood. Fix: IGMP […]