200 CHAPTER 16: IGMP SNOOPING CONFIGURATION
the forwarding entry corresponding to that port from the forwarding table;
instead, it resets the aging timer of the member port.
Upon receiving the IGMP leave message from a host, the IGMP querier resolves
from the message the address of the multicast group that the host just left and
sends an IGMP group-specific query to that multicast group through the port that
received the leave message. Upon receiving the IGMP group-specific query, a
switch forwards it through all the router ports in the VLAN and all member ports
of that multicast group, and performs the following to the receiving port:
■ If any IGMP report in response to the group-specific query arrives to the
member port before its aging timer expires, this means that some other
members of that multicast group still exist under that port: the switch resets
the aging timer of the member port.
■ If no IGMP report in response to the group-specific query arrives to the
member port before its aging timer expires as a response to the IGMP
group-specific query, this means that no members of that multicast group still
exist under the port: the switch deletes the forwarding entry corresponding to
the port from the forwarding table when the aging timer expires.
c
Caution: After an Ethernet switch enables IGMP Snooping, when it receives the
IGMP leave message sent by a host in a multicast group, it judges whether the
multicast group exists automatically. If the multicast group does not exist, the
switch drops this IGMP leave message.
IGMP Snooping
Configuration
The following table lists all the IGMP Snooping configuration tasks:
Enabling IGMP Snooping
Tabl e 145 IGMP Snooping configuration tasks
Operation Remarks
Enabling IGMP Snooping Required
Configuring the Version of IGMP Snooping Optional
Configuring Timers Optional
Configuring Fast Leave Optional
Configuring a Multicast Group Filter Optional
Configuring the Maximum Number of Multicast Groups on a Port Optional
Configuring Static Member Port for a Multicast Group Optional
Configuring a Static Router Port Optional
Configuring a Port as a Simulated Group Member Optional
Configuring a VLAN Tag for Query Message Optional
Tabl e 146 Enable IGMP Snooping
Operation Command Remarks
Enter system view system-view -
Enable IGMP Snooping
globally
igmp-snooping enable Required
By default, IGMP Snooping is
disabled globally.
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