NetComm NB9 User Giude page 53

Field
Save
Save / Reboot
NB9/NB9W ADSL2+ VoIP Router
YML790 Rev1
Means
Without IGMP snooping, multicast traffic is treated
in the same manner as broadcast traffic - that is, it
is forwarded to all ports. With IGMP snooping,
multicast traffic of a group is only forwarded to ports
that have members of that group. IGMP Snooping
generates no additional network traffic, allowing
you to significantly reduce multicast traffic passing
through your NB9/NB9W.
Save the settings.
Save and reboot with the settings applied.
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