3Com Switch 7750 Configuration Guide Guide

Overview 389
c
CAUTION: An IGMP-Snooping-enabled Switch 7750 Family Ethernet switch
judges whether the multicast group exists when it receives an IGMP leave packet
sent by a host in a multicast group. If this multicast group does not exist, the
switch will drop the IGMP leave packet instead of forwarding it.
IGMP
leave
message
Host
Multicast
router
and
multicast
switch
Notify
the
multicast
router
and
multicast
switch
that the
host is
leaving
its
multicast
group.
Multicast router and multicast
switch send IGMP specific group
query packet(s) to the multicast
group whose member host
sends leave packets to check if
the multicast group has any
members and enable the
corresponding query timer.
If the multicast
group
responds, the
switch checks
whether the
port is the last
host port
corresponding
to the MAC
multicast
group.
■ If yes,
remove the
correspondi
ng 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
correspondi
ng 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
Table 305 IGMP Snooping messages
Message Sender Receiver Purpose Action of the multicast member switch