#readwise # What Is the Internet Group Management Protocol (IGMP)?  ## Metadata - Author: [[cloudflare.com]] - Full Title: What Is the Internet Group Management Protocol (IGMP)? - URL: https://www.cloudflare.com/learning/network-layer/what-is-igmp/ ## Highlights The Internet Group Management Protocol (IGMP) is a protocol that allows several devices to share one IP address so they can all receive the same data. **IGMP is a network layer [protocol](https://www.cloudflare.com/learning/network-layer/what-is-a-protocol/) used to set up multicasting on networks that use the [Internet Protocol](https://www.cloudflare.com/learning/network-layer/internet-protocol/) version 4 (IPv4). Specifically, IGMP allows devices to join a multicasting group.** ([View Highlight](https://read.readwise.io/read/01j5xg8g9qm3ze7v1hnrv8cbbb)) ^dv1d4p --- Multicasting is when a group of devices all receive the same messages or [packets](https://www.cloudflare.com/learning/network-layer/what-is-a-packet/). Multicasting works by sharing an IP address between multiple devices. Any network traffic directed at that [IP address](https://www.cloudflare.com/learning/dns/glossary/what-is-my-ip-address/) will reach all devices that share the IP address, instead of just one device. This is much like when a group of employees all receive company emails directed at a certain email alias. ([View Highlight](https://read.readwise.io/read/01j5xg8khnqpwe61rbx6s1ab96)) --- **Computers and other devices connected to a network use IGMP when they want to join a multicast group. A router that supports IGMP listens to IGMP transmissions from devices in order to figure out which devices belong to which multicast groups.** IGMP uses IP addresses that are set aside for multicasting. Multicast IP addresses are in the range between 224.0.0.0 and 239.255.255.255. (In contrast, anycast networks can use any regular IP address.) Each multicast group shares one of these IP addresses. **When a router receives a series of packets directed at the shared IP address, it will duplicate those packets, sending copies to all members of the multicast group.** IGMP multicast groups can change at any time. **A device can send an IGMP "join group" or "leave group" message at any point.** ([View Highlight](https://read.readwise.io/read/01j5xgc8qwhgn7bxrb4185zh71)) ^n1c9i1 ---