HP 6125G Configuration Manual page 27

Figure 12 Network diagram
IP network
Proxy & Querier
Switch A
Host A
Receiver
As shown in Figure 12, Switch A works as an IGMP snooping proxy. As a host from the perspective of the
querier Router A, Switch A represents its attached hosts to send membership reports and leave messages
to Router A.
Table 6 IGMP message processing on an IGMP snooping proxy
IGMP message
General query
Group-specific query
Report
Leave
IGMP Querier
Router A
Host C
Receiver
Host B
Actions
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 of all router ports.
In response to the IGMP group-specific query for a certain multicast
group, the proxy sends the report to the group out of all router ports if the
forwarding entry for the group still contains a member port.
After receiving a report for a multicast group, the proxy looks up the
multicast forwarding table for the forwarding entry for the multicast
group.
•
If a forwarding entry matches the multicast group and contains the
receiving port as a dynamic member port, the proxy restarts the
aging timer for the port.
•
If a forwarding entry matches the multicast group but does not
contain the receiving port, the proxy adds the port to the forwarding
entry as a dynamic member port and starts an aging timer for the
port.
•
If no forwarding entry matches the multicast group, the proxy creates
a forwarding entry for the multicast group, adds the receiving port to
the forwarding entry as a dynamic member port, and starts an aging
timer for the port.
In response to an IGMP leave message for a multicast group, the proxy
sends a group-specific query out of 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 of all
router ports.
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Query from Router A
Report from Switch A
Query from Switch A
Report from Host