16
Figure 12
Network diagram
As shown in
, 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 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 of 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 of all router ports if the
forwarding entry for the group still contains a member port.
Report
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.
Leave
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.
Host A
Receiver
Host B
Host C
Receiver
IGMP Querier
Router A
Proxy & Querier
Switch A
Query from Router A
Report from Switch A
Query from Switch A
Report from Host
IP network
