L
AYER
2 IGMP (S
NOOPING
AND
Q
UERY
)
14-3
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 the multicast filters
accordingly.
• IGMP Querier – 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 upstream 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: Disabled)
• 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. (Range: 2-10, Default: 2)
• IGMP Query Interval — Sets the frequency 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
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