3Com 4200G 12-Port Configuration Manual page 265

Table 221 IGMP Snooping messages
Message Sender
IGMP general Multicast
query router and
message multicast
switch
IGMP Multicast
group-specifi router and
c query multicast
message switch
IGMP host Host
report
message
IGMP leave Host
message
To implement Layer 2 multicast, the switch processes four different types of IGMP
messages it received, as shown in Table 221.
Receiver Purpose
Multicast Query if the
member multicast
switch and groups
host contain any
member
Multicast Query if a
member specific
switch and multicast
host group
contains any
member
Multicast Apply for
router and joining a
multicast multicast
switch group, or
respond to
an IGMP
query
message
Multicast Notify the
router and multicast
multicast router and
switch multicast
switch that
the host is
leaving its
multicast
group.
Switch action
Check if the message comes from
the original router port
Send a group-specific query message to the IP multicast group being
queried.
Check if the If yes, check if
IP multicast the port exists
group has a in the MAC
correspondi multicast
ng MAC group.
multicast
group
If not:
Create a MAC multicast group and notify the multicast
router that a member is ready to join the multicast group.
Add the port to the MAC multicast group and start the
aging timer of the port.
Add all router ports in the VLAN owning this port to the
forward port list of the MAC multicast group.
Add the port to the IP multicast group.
Multicast router and multicast switch send
group-specific query packet(s) to the port
receiving the leave message to check if the
port has any member, and start the
corresponding query response timer.
Overview of IGMP Snooping 251
If yes, reset the aging timer of the
router port.
If not, notify the multicast router
that a member is in a multicast
group and start the aging timer for
the router port.
If yes, add the IP multicast group address
to the MAC multicast group table.
If not, add the port to If yes, add the
the MAC multicast port to the IP
group, trigger the multicast group.
aging timer of the port
If not, create an
and check if the
IP multicast
corresponding IP
group and add
multicast group exists.
the port to it.
If no response is received
from the port before the
timer times out, the
switch will check whether
the port corresponds to a
single MAC multicast
group.
If yes, remove the
corresponding MAC
multicast group and IP
multicast group.
If no, remove only
those entries that
correspond to this port in
the MAC multicast group,
and remove the
corresponding IP multicast
group entries.
If no response is received
from the multicast group
before the timer times
out, notify the router to
remove this multicast
group node from the
multicast tree.