H3C Technologies H3C WX3000E Series Wireless Switches - Manual (Page 13)

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The ports in this section are dynamic port. Static ports can be added or deleted only through the
corresponding configurations. For more information, see " Configuring static ports ."
When receiving a general query
The IGMP querier periodically sends IGMP general queries to all hosts and routers identified by the
address 224.0.0.1 on the local subnet to determine whether active multicast group members exist on the
subnet.
After receiving an IGMP general query, the Layer 2 device forwards it through all ports in the VLAN
(except the receiving port). The Layer 2 device also performs one of the following actions:
• If the receiving port is a dynamic router port in the router port list, resets the aging timer of this
dynamic router port.
• If the receiving port is not a dynamic router port in the router port list, adds it into its router port list
and sets an aging timer for this dynamic router port.
When receiving a membership report
A host sends an IGMP report to the IGMP querier for the following purposes:
• If the host has been a multicast group member, responds with an IGMP report.
• Applies for joining a multicast group.
After receiving an IGMP report, the Layer 2 device forwards it through all the router ports in the VLAN,
resolves the address of the reported multicast group. The Layer 2 device also one of the following actions:
• If no forwarding table entry matches the group address, creates a forwarding entry, adds the
receiving port as a dynamic member port to the outgoing port list, and starts a member port aging
timer for that port.
• If a forwarding table entry matches the group address, but the receiving port is not included in the
outgoing port list for that group, adds the port as a dynamic member port to the outgoing port list
and starts an aging timer for that port.
• If a forwarding table entry matches the group address and the port is included in the outgoing port
list, resets the aging timer for that port.
A Layer 2 device does not forward an IGMP report through a non-router port. If the Layer 2 device
forwards a report message through a member port, the IGMP report suppression mechanism causes all
the attached hosts that are monitoring the reported multicast address to suppress their own reports. This
makes the Layer 2 device unable to know whether the reported multicast group still has active members
attached to that port.
When receiving a leave message
When an IGMPv1 host leaves a multicast group, the host does not send an IGMP leave message, so the
Layer 2 device cannot know immediately that the host has left the multicast group. However, as the host
stops sending IGMP reports as soon as it leaves a multicast group, the Layer 2 device deletes the
forwarding entry for the dynamic member port that corresponds to the host from the forwarding table
when its aging timer expires.
When an IGMPv2 or IGMPv3 host leaves a multicast group, the host sends an IGMP leave message to
the multicast router.
When the Layer 2 device receives an IGMP leave message on a dynamic member port, the Layer 2
device first examines whether a forwarding table entry for the group address in the message exists, and,
if one exists, whether the outgoing port list contains the port.
• If the forwarding table entry does not exist or if the outgoing port list does not contain the port,
discards the IGMP leave message instead of forwarding it to any port.