What happens when a multicast packet is sent across a network switch without IGMP snooping?

When a multicast packet is sent across a network switch without IGMP snooping, the packet is received by all devices on the network. This occurs because, in the absence of IGMP snooping, the switch does not have the capability to filter multicast traffic based on the subscriptions of the connected devices.

Without IGMP snooping, the switch treats multicast packets similarly to broadcast packets, forwarding them to all ports except the one from which they were received. As a result, every device connected to the switch will receive the multicast packet, which can lead to unnecessary network congestion, especially if many devices are not interested in the multicast stream. This situation emphasizes the importance of IGMP snooping, which allows the switch to intelligently forward multicast packets only to those ports where devices have expressed interest in receiving them.