Igmp Snooping; Igmp Groups - Lenovo Flex System Fabric CN4093 Application Manual

IGMP Snooping

IGMP Groups

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CN4093 Application Guide for N/OS 8.2
IGMP Snooping allows the switch to forward multicast traffic only to those ports
that request it. IGMP Snooping prevents multicast traffic from being flooded to all
ports. The switch learns which server hosts are interested in receiving multicast
traffic, and forwards it only to ports connected to those servers.
IGMP Snooping conserves bandwidth. With IGMP Snooping, the switch learns
which ports are interested in receiving multicast data, and forwards multicast data
only to those ports. In this way, other ports are not burdened with unwanted
multicast traffic.
The switch can sense IGMP Membership Reports from attached clients and act as a
proxy to set up a dedicated path between the requesting host and a local IPv4
Multicast router. After the pathway is established, the switch blocks the IPv4
Multicast stream from flowing through any port that does not connect to a host
member, thus conserving bandwidth.
The client‐server path is set up as follows:
 An IPv4 Multicast Router (Mrouter) sends Membership Queries to the switch,
which forwards them to all ports in a given VLAN.
Hosts that want to receive the multicast data stream send Membership Reports to

the switch, which sends a proxy Membership Report to the Mrouter.
The switch sets up a path between the Mrouter and the host, and blocks all other

ports from receiving the multicast.
 Periodically, the Mrouter sends Membership Queries to ensure that the host
wants to continue receiving the multicast. If a host fails to respond with a
Membership Report, the Mrouter stops sending the multicast to that path.
The host can send an IGMP Leave packet to the switch, which responds with an

IGMP Groups Specific Query in order to check if there are other clients that
want to receive the multicast traffic for the group referenced in the Leave packet.
If an IGMP Report is not received, the group is deleted from the port and the
multicast path is terminated. The switch then sends a Proxy Leave packet to the
Mrouter in order to update it. If the FastLeave option is enabled on a VLAN, the
multicast path is terminated immediately and the Leave packet is directly
forwarded to the Mrouter.
The CN4093 supports a maximum of 3072 IGMP entries, on a maximum of 1024
(1022 in stacking mode) VLANs. One IGMP entry is allocated for each unique join
request, based on the VLAN and IGMP group address only (regardless of the
port). If multiple ports join the same IGMP group using the same VLAN, only a
single IGMP entry is used.