H3C Technologies H3C WX3000E Series Wireless Switches - Manual (Page 15)

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Figure 4 Network diagram for IGMP snooping proxying
As shown in Figure 4 , AC works as an IGMP snooping proxy. As a host from the perspective of the
querier Router A, AC represents its attached hosts to send membership reports and leave messages to the
router.
Table 1 IGMP message processing on an IGMP snooping proxy
IGMP message Actions
General query
When receiving an IGMP general query, the proxy forwards it to all ports but the
receiving port. In addition, the proxy generates a report according to the group
memberships it maintains and sends the report out all router ports.
Group-specific
query
In response to the IGMP group-specific query for a certain multicast group, the proxy
sends the report to the group out all router ports if the forwarding entry for the group still
contains a member port.
Report
When receiving a report for a multicast group, the proxy looks up the multicast
forwarding table for the entry for the multicast group. If the forwarding entry is found with
the receiving port contained as a dynamic member port in the outgoing port list, the proxy
resets the aging timer for the entry. If the forwarding entry is found but the outgoing port
list does not include the receiving port, the proxy adds the port to the outgoing port list as
a dynamic member port and starts an aging timer for it. If no forwarding entry is found,
the proxy creates the entry, adds the receiving port to the outgoing port list as a dynamic
member port and starts an aging timer for the port. Then, it sends a report to the group out
all router ports.
Leave
In response to an IGMP leave message for a multicast group, the proxy sends a
group-specific query out the receiving port. After making sure that no member port is
contained in the forwarding entry for the multicast group, the proxy sends a leave
message to the group out all router ports.