H3C Technologies H3C S12500-X Series Switches - Manual (Page 26)

16
Timer Description
Expected messages
before the timer expires
Action after the timer
expires
Dynamic
member port
aging timer
When a port dynamically joins a
multicast group, the switch starts or
resets an aging timer for the port.
IGMP membership report.
The switch removes the
port from the IGMP
snooping forwarding
table.
NOTE:
In IGMP snooping, only dynamic ports age out. Static ports never age out.
How IGMP snooping works
The ports in this section are dynamic ports. For information about how to configure and remove static
ports, see "
Configuring static ports ."
IGMP messages types include general query, IGMP report, and leave message. An IGMP
snooping-enabled switch performs differently depending on the message.
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 any active multicast group members exist on
the subnet.
After receiving an IGMP general query, the switch forwards the query to all ports in the VLAN except the
port that received the query. The switch also performs one of the following actions:
• If the receiving port is a dynamic router port in the router port list, the switch restarts the aging timer
for the port.
• If the receiving port does not exist in the router port list, the switch adds the port to the router port
list, and starts an aging timer for the port.
IGMP report
A host sends an IGMP report to the IGMP querier for the following purposes:
• Responds to queries if the host is a multicast group member.
• Applies for a multicast group membership.
After receiving an IGMP report from the host, the switch forwards it through all the router ports in the
VLAN, resolves the address of the reported multicast group, and performs one of the following actions:
• If no forwarding entry matches the group address, the switch creates a forwarding entry for the
group, adds the receiving port as a dynamic member port to the forwarding entry, and starts an
aging timer for the port.
• If a forwarding entry matches the group address, but the receiving port is not in the forwarding
entry for the group, the switch adds the port as a dynamic member port to the forwarding entry, and
starts an aging timer for the port.
• If a forwarding entry matches the group address and the receiving port is in the forwarding entry
for the group, the switch restarts the aging timer for the port.
In an application with a group filter configured on an IGMP snooping-enabled switch, when a user
requests a multicast program, the user's host initiates an IGMP report. After receiving this report, the
switch resolves the multicast group address in the report and looks up the ACL. If a match is found to