3Com 4007, Implementation Manual, Page: 214 / 684

214 C
HAPTER
11: IP M
ULTICAST
F
ILTERING WITH
IGMP
If the switch flooded IGMP reports, hosts on other segments would
suppress their own reports for identical groups, which would cause the
switch to set overly restrictive filters. Restricted forwarding of IGMP
reports is necessary to allow the switch to receive IGMP reports from at
least one host per group on each of its ports.
Configuring IGMP
in Your System
Layer 2 Switching Modules support IGMP version 1 (RFC 1112) and
version 2 (RFC 2236). You can manage the following IGMP options:
■
Enable or disable the snooping function and the querying function.
■
Both settings apply to all ports on the module.
■
Both settings are disabled by default.
■
If enabled, the querying function requires that you configure a
source IP address. See “Operating as the Querier” later in this
chapter.
■
Display a command configuration summary
■
Display VLANs with active snooping activity
■
Display group and port information per VLAN
■
Display the designated querier per VLAN
■
Display IP multicast router ports per VLAN
■
Display the port in the VLAN that last received a query
With snooping and querying enabled, your switching module:
■
Builds for each VLAN a table of member ports per IP multicast group
and adjusts the table over time through an aging mechanism as well
as by processing IGMP messages.
■
Sets per-port filters that allow targeted forwarding of IP multicast
group traffic.
■
Determines which ports lead to routers. See “Locating Multicast
Routers” in this chapter.
■
Determines which port leads to the querier (unless the module is the
querier). See “Operating as the Querier” in this chapter.
■
Supports a private IGMP Snooping MIB (
3cigmpSnoop.mib
).