ZyXEL Communications SAM1316-22, User Manual

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Chapter 18 IGMP
SAM1316-22 User’s Guide
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that are members of that group. The SAM1316-22 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.
18.2.2 IGMP Proxy
To allow better network performance, you can use IGMP proxy instead of a
multicast routing protocol in a simple tree network topology.
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 SAM1316-22. A downstream interface is a port that connects to a host
(such as a computer).
The following figure shows a network example where A is the multicast source
while computers 1, 2 and 3 are the receivers. In the figure A is connected to the
upstream interface and 1, 2 and 3 are connected to the downstream interface.
Figure 67 IGMP Proxy Network Example
The SAM1316-22 will not respond to IGMP join and leave messages on the
upstream interface. The SAM1316-22 only responds to IGMP query messages on
the upstream interface. The SAM1316-22 sends IGMP query messages to the
hosts that are members of the query VLAN.