IGMP snooping allows a switch to only forward multicast traffic to the links that have solicited them. IGMP snooping takes place internally on switches and is not a protocol feature.
It provides switches with a mechanism to prune multicast traffic from links that do not contain a multicast listener (an IGMP client).Įssentially, IGMP snooping is a layer 2 optimization for the layer 3 IGMP. IGMP snooping is designed to prevent hosts on a local network from receiving traffic for a multicast group they have not explicitly joined. When purposefully exploited, this can form the basis of a denial-of-service attack. Multicast can cause unnecessary load on host devices by requiring them to process packets they have not solicited. The join message so that Switch can more easily determine when a group has noĭefined in RFC 3376.A switch will, by default, flood multicast traffic to all the ports in a broadcast domain (or the VLAN equivalent). To the Switch, but a timeout is used to determine when hosts leave a group.ĭefined in RFC 2236. Without IGMP Snooping, Multicast traffic is treated in the same manner as a Broadcast transmission, which forwards packets to all ports on the network.ĭefined in RFC 1112. IGMP Snooping significantly reduces overall Multicast traffic passing through your Switch. This improves network performance by restricting the multicast packets only to Switch ports where host nodes are located. The Switch can also limit flooding of traffic to IGMP designated ports. It enables the Switch to forward packets of multicast groups to those ports that have validated host nodes. Based on the IGMP query and report messages, the Switch forwards traffic only to the ports that request the multicast traffic. IGMP Snooping checks IGMP packets passing through the network and configures Multicasting accordingly. Any multicast packets belonging to that multicast group are then forwarded by the Switch from the port.Ī Switch supporting IGMP Snooping can passively snoop on IGMP Query, Report, and Leave packets transferred between IP Multicast Switches and IP Multicast hosts to determine the IP Multicast group membership. After joining a multicast group, a host node must continue to periodically issue reports to remain a member. It merely broadcasts its service to the network, and any host that wishes to receive the multicast register with their local multicast Switch.Ī multicast group is a group of end nodes that want to receive multicast packets from a multicast application. A multicast server does not have to establish a separate connection with each client.
Multicasting is used to support real-time applications such as videoconferencing or streaming audio.
Internet Group Management Protocol (IGMP) Snooping allows a Switch to forward multicast traffic intelligently.
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