Work Mechanism Of Igmp Snooping - H3C S3100-52P Operation Manual

Operation Manual – Multicast
H3C S3100-52P Ethernet Switch
Router port: A router port is a port on the Layer 3 multicast device (DR or IGMP
querier) side of the Ethernet switch. In the figure, Ethernet 1/0/1 of Switch A and
Ethernet 1/0/1 of Switch B are router ports. A switch registers all its local router
ports in its router port list.
Member port: A member port is a port on the multicast group member side of the
Ethernet switch. In the figure, Ethernet 1/0/2 and Ethernet 1/0/3 of Switch A and
Ethernet 1/0/2 of Switch B are member ports. The switch records all member ports
on the local device in the IGMP Snooping forwarding table.
II. Port aging timers in IGMP Snooping and related messages and actions
Table 3-1 Port aging timers in IGMP Snooping and related messages and actions
Timer
Router port
aging timer
Member port
aging timer

3.1.3 Work Mechanism of IGMP Snooping

A switch running IGMP Snooping performs different actions when it receives different
IGMP messages, as follows:
I. When receiving a general query
The IGMP querier periodically sends IGMP general queries to all hosts and routers on
the local subnet to find out whether active multicast group members exist on the
subnet.
Upon receiving an IGMP general query, the switch forwards it through all ports in the
VLAN except the receiving port and performs the following to the receiving port:
If the receiving port is a router port existing in its router port list, the switch resets
the aging timer of this router port.
If the receiving port is not a router port existing in its router port list, the switch adds
it into its router port list and sets an aging timer for this router port.
II. When receiving a membership report
A host sends an IGMP report to the multicast router in the following circumstances:
Description
For each router port, the
switch sets a timer
initialized to the aging
time of the route port
When a port joins a
multicast group, the
switch sets a timer for
the port, which is
initialized to the member
port aging time
3-3
Chapter 3 IGMP Snooping Configuration
Message before
expiry
IGMP general
query or PIM hello
IGMP membership
report
Action after
expiry
The switch
removes this port
from its router port
list
The switch
removes this port
from the multicast
group forwarding
table