Nimbus Water Systems WIMI6200, User Manual, Page: 66 / 72

WiMi6200 User’s Manual

IGMP Snooping Function of the L2 Ethernet switch
A switch will, by default, flood multicast traffic to all the ports in a broadcast domain
(or the VLAN equivalent). Multicast can cause unnecessary load on host devices by
requiring them to process packets they have not solicited. When purposefully
exploited this is known as one variation of a denial-of-service attack. IGMP snooping
is designed to prevent hosts on a local network from receiving traffic for a multicast
group they have not explicitly joined. It provides switches with a mechanism to prune
multicast traffic from links that do not contain a multicast listener (an IGMP client).
IGMP snooping allows a switch to only forward multicast traffic to the links that have
solicited them. Essentially, IGMP snooping is a layer 2 optimization for the layer 3
IGMP. IGMP snooping takes place internally on switches and is not a protocol feature.
Snooping is therefore especially useful for bandwidth-intensive IP multicast
applications such as IPTV.

IGMP querier
In order for IGMP, and thus IGMP snooping, to function, a multicast router must exist
on the network and generate IGMP queries. The tables created for snooping (holding
the member ports for each a multicast group) are associated with the querier. Without
a querier the tables are not created and snooping will not work. Furthermore IGMP
general queries must be unconditionally forwarded by all switches involved in IGMP
snooping. Some IGMP snooping implementations include full querier capability.
Others are able to proxy and retransmit queries from the multicast router.
 Prerequisites for multicasting A/V over IP network
There must be one or more Multicast routers on the network to transport multicast
A/V traffic on the network that the single WiMi4000T/6200T/6400T and multiple
WiMi4000R/6200R/6400R are working. And all the L2 Ethernet switches on the
network between the WiMi4000T/6200T/6400T and WiMi4000R/6200R/6400R must
support IGMP snooping function. If there is a L2 Ethernet switch that does not
support IGMP snooping function, then the multicast A/V traffic will be flooded to
every ports that can be resulted in blocking the multicast A/V traffic.

Multicasting A/V over single sub-network
There is one simple solution for replacing an expensive multicast router, if the
multicasting is transmitted and received in one sub-network. Some of advanced L2
Ethernet switch transmits IGMP query packets through their Ethernet port. If there is
no need to multicast IP traffic over the different sub-network, then you can use this
cheap L2 Ethernet switch. The one sample of this advanced L2 switch that Nimbus has
tested is the HP’s
V1910-16G Switch (JE005A)
.
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