Configuring the Switch
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3
IGMP Query (Layer 2 or 3) – IGMP Query can only be enabled globally at Layer 2,
but can be enabled for individual VLAN interfaces at Layer 3 (page 3-149). However,
note that Layer 2 query is disabled if Layer 3 query is enabled.
Configuring IGMP Snooping and Query Parameters
You can configure the switch to forward multicast traffic intelligently. Based on the
IGMP query and report messages, the switch forwards traffic only to the ports that
request multicast traffic. This prevents the switch from broadcasting the traffic to all
ports and possibly disrupting network performance.
Command Usage
• IGMP Snooping – This switch can passively snoop on IGMP Query and Report
packets transferred between IP multicast routers/switches and IP multicast host
groups to identify the IP multicast group members. It simply monitors the IGMP
packets passing through it, picks out the group registration information, and
configures multicast filters accordingly.
• IGMP Query – A router, or multicast-enabled switch, can periodically ask their
hosts if they want to receive multicast traffic. If there is more than one router/switch
on the LAN performing IP multicasting, one of these devices is elected “querier”
and assumes the role of querying the LAN for group members. It then propagates
the service requests on to any adjacent multicast switch/router to ensure that it will
continue to receive the multicast service.
Note: Multicast routers use this information, along with a multicast routing protocol such
as DVMRP or PIM, to support IP multicasting across the Internet.
Command Attributes
• IGMP Status — When enabled, the switch will monitor network traffic to determine
which hosts want to receive multicast traffic. This is also referred to as
IGMP Snooping. (Default: Enabled)
• Act as IGMP Querier — When enabled, the switch can serve as the Querier,
which is responsible for asking hosts if they want to receive multicast traffic.
(Default: Enabled)
• IGMP Query Count — Sets the maximum number of queries issued for which
there has been no response before the switch takes action to drop a client from the
multicast group. (Default: 2, Range: 2 - 10)
• IGMP Query Interval — Sets the frequency of time at which the switch sends
IGMP host-query messages. (Range: 60 - 125 seconds; Default: 125.)
• IGMP Report Delay — Sets the time between receiving an IGMP Report for an IP
multicast address on a port before the switch sends an IGMP Query out of that port
and removes the entry from its list. (Range: 5-30 seconds; Default: 10)
• Query Timeout — Sets the time the switch waits after the previous querier has
stopped querying before it takes over as the querier. (Range: 300-500 seconds;
Default: 300)
• IGMP Version — Sets the protocol version for compatibility with other devices on
the network. (Range: 1-2; Default: 2)
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