Allied Telesis SwitchBlade x3100 Series Manual page 539

Configuring IGMP
MCPASSTHROUGH - IGMP Snooping will filter IGMP packets and will flood all mulitcast traffic that is
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received from the mulitcast router to network interfaces that are set to MCPASSTHROUGH and are a
member of the VLAN.
INTERNAL (snooping) - The interface will reconfigure the hardware to limit forwarding of mulitcast packets
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only to the ports that have expressed interest in the multicast group.
EXTERNAL (limited snooping) - Behind the interface towards the customer is a device that has a snooping
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function. The SBx3112 interface will only snoop for the first IGMP Report and the last IGMP Leave message,
when it knows that there is no more interest for the specific multicast stream on the downstream device.
For Figure 5-1, the interfaces could be configured as follows:
SBX3112-B and SBx3112 - C - The link (4) is part of a ring and connects the two SBx3112s. Interfaces 0.2
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and 2.1 are configured as:
DIRECTION = NETWORK
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SNOOPINGMODE = MCPASSTHROUGH
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SBX3112-B - The link (5) is to a device that provides IGMP, and so interface 0.3 is configured as:
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DIRECTION = CUSTOMER
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SNOOPINGMODE = EXTERNAL
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SBX3112-C - The link (6) is to a device that does not provide IGMP, and so interface 6.0 is configured as:
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DIRECTION = CUSTOMER
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SNOOPINGMODE = INTERNAL
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Refer to the SET IGMPSNOOPING
5.3.5 Restrictions and Limitations
The number of IGMP groups can be set from 1 up to 512, depending on bandwidth requirements (usually for
the number of video channels). Note that when the number of IGMP groups reaches 80% of the configured
number, a management log is produced, and at 100% an alarm is produced.
MAC limiting restricts the ability to learn MAC addresses on a port. When the MAC learning limit is reached,
all frames from MAC sources that are not already in the FDB are dropped. This could be part of a subscriber's
Service Level Agreement.
5.3.6 Configuration Procedure
Figure 5-2 demonstrates an IGMP multicast group that is formed -- using a video VLAN -- and set up with two
customer hosts. The network includes an SBx3112 connected to a customer STB (on link 2), to another cus-
tomer STB (on link 3) via an iMG616 gateway (serving as an IGMP proxy modem), and to the network via a
multicast router (on link 1).
Software Reference for SwitchBlade x3100 Series Switches (Internet Group Management Pro-
tocol (IGMP))
command.
Introduction
5-7