3Com Switch 8807, Configuration Manual

Page: 421 / 883

IGMP Snooping Overview 421
Figure 104 Implement IGMP Snooping
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IGMP general query message: Transmitted by the multicast router to the
multicast group members to query which multicast group contains member.
When an IGMP general query message arrives at a router port, the Ethernet
switch will reset the aging timer of the port. When a port other than a router
port receives the IGMP general query message, the Ethernet switch will start
the aging timer for the port.
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IGMP specific query message: Transmitted from the multicast router to the
multicast members and used for querying if a specific group contains any
member. When received IGMP specific query message, the switch only
transmits the specific query message to the IP multicast group which is queried.
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IGMP report message: Transmitted from the host to the multicast router and
used for applying for joining a multicast group or responding to the IGMP
query message. When received the IGMP report message, the switch checks if
the MAC multicast group, corresponding to the IP multicast group the packet is
ready to join exists.
If the corresponding MAC multicast group does not exist, the switch only notifies
the router that a member is ready to join a multicast group, creates a new MAC
multicast group, adds the port received the message to the group, starts the port
aging timer, and then adds all the router ports in the native VLAN of the port into
the MAC multicast forwarding table, and meanwhile creates an IP multicast group
and adds the port received the report message to it.
If the corresponding MAC multicast group exists but does not contains the port
received the report message, the switch adds the port into the multicast group
and starts the port aging timer. And then the switch checks if the corresponding IP
multicast group exists.
If it does not exist, the switch creates a new IP multicast group and adds the port
received the report message to it. If it exists, the switch adds the port to it.
If the MAC multicast group corresponding to the message exists and contains the
port received the message, the switch will only reset the aging timer of the port.
Internet
IGMP packets
A Ethernet Switch
running IGMP Snooping
A
router
running IGMP
IGMP packets
Internet
IGMP packets
A Ethernet switch
running IGMP Snooping
A
router
running IGMP
IGMP packets