ZyXEL Communications VSG1432-B101 Series User Manual

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Chapter 14 IGMP
VSG1432-B101 Series User’s Guide
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multicast hosts to learn the IP multicast group membership. It checks IGMP 
packets passing through it, picks out the group registration information, and 
configures multicasting accordingly. IGMP snooping allows the ZyXEL Device to 
learn multicast groups without you having to manually configure them.
The ZyXEL Device forwards multicast traffic destined for multicast groups (that it 
has learned from IGMP snooping or that you have manually configured) to ports 
that are members of that group. The ZyXEL Device discards multicast traffic 
destined for multicast groups that it does not know. IGMP snooping generates no 
additional network traffic, allowing you to significantly reduce multicast traffic 
passing through your device.
IGMP Proxy
To allow better network performance, you can use IGMP proxy instead of a 
multicast routing protocol in a simple tree network topology. 
Note: Your ZyXEL Device is an IGMP proxy.
In IGMP proxy, an upstream interface is the port that is closer to the source (or 
the root of the multicast tree) and is able to receive multicast traffic. There should 
only be one upstream interface (also known as the query port) for one query VLAN 
on the ZyXEL Device. A downstream interface is a port that connects to a host 
(such as a computer).