3Com 4007, Implementation Manual, Page: 215 / 684

Key Implementation Guidelines 215
Key
Implementation
Guidelines
Consider these points when you configure IGMP options in a Layer 2
Switching Module:
■
IGMP snooping and querying works for IP multicast packets only.
Other protocol-based multicast packets are flooded to all ports in
compliance with the IEEE 8021.D standard.
■
Each IGMP-capable device performs snooping for its own ports, but
only one device in a subnetwork or broadcast domain acts as the
querier for all devices. Thus, on a single switching module, you can
enable snooping and disable querying as long as one or more other
devices in the subnetwork or broadcast domain can act as the querier.
■
If you enable querying on a given module, you must also enable
snooping for querying to work properly.
■
To maximize the effectiveness of IGMP in a flat network design or
large broadcast domain that includes IP multicast sources, the querier
should be positioned as close to the source of IP multicast traffic
(usually servers) as possible. You can accomplish this by enabling the
query function only on certain devices.
■
Because some IP multicast applications transmit a large number of
unsolicited packets or may require security protection, 3Com
recommends that you place IP multicast sources upstream from a
Layer 3 switch or router.