ZyXEL Communications MSC1000G Series, User Manual

Page: 186 / 1168

Chapter 8 Multicast Screens
Management Switch Card User’s Guide
186
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) on the system to limit bandwidth use. A downstream interface is a
port that connects to a host (such as a computer). A query VLAN determines which ports are
downstream interfaces.
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 111
IGMP Proxy Network Example
The system will not respond to IGMP join and leave messages on the upstream interface. The
system only responds to IGMP query messages on the upstream interface. The system sends IGMP
query messages to the hosts that are members of the query VLAN.
The system only sends an IGMP leave messages via the upstream interface when the last host
leaves a multicast group.
One of the Ethernet ports acts as the upstream interface. By default, the DSL ports are set as the
downstream interfaces.
Note: The switch does not allow a subscriber port to send multicast traffic (except static
multicast traffic) to an uplink port. Only the uplink port can forward multicast traffic
to the subscriber port(s).
8.1.4 IGMP Snooping and Proxy Note
The IES acts as an IGMPv3 client host for an edge IGMPv3 multicast router and as a IGMPv2/v3
router for IGMPv2/v3 client hosts (subscribers). The IES can recognize IGMPv3 protocol messages
and forward them towards the IGMP multicast router. It does not support full-featured IGMPv3
functions like source IP address control specified in RFC 3376.
A
1 2
3