Jan 6, 2017
Today I learned about IGMP, which stands for Internet Group Message Protocol. There are three different ways packets are sent out to other devices. There’s unicast, which just sends a packet to one specific device. Then there’s broadcast, which sends packets to all the devices that is in the network. Lastly, there’s multicast. Multicast sends packets to more than one device but not all the devices.
If a device wants to be part of a multicast group, it sends out an IGMP packet, or more specifically, an IGMP join packet. The join packet expresses the device’s desire to subscribe to the multicast feed.
Usually, a switch is the receiving end of this join request. If IGMP snooping is enabled on the switch, it will listen for requests and add the device to the group.