H3C Technologies H3C S7500E Series Switches - Manual (Page 39)

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Figure 2-3 Network diagram for IGMP snooping proxying
As shown in Figure 2-3 , Switch A works as an IGMP Snooping proxy. It represents its attached
hosts to send membership reports and leave messages to Router A.
Table 2-2 describes how an IGMP snooping proxy processes IGMP messages.
Table 2-2 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, and then, 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.