Switch 7700 Configuration Guide

118 CHAPTER 6: MULTICAST PROTOCOL
Figure 6 Implementing IGMP Snooping
1 IGMP general query message: Transmitted by the multicast router to query which
multicast group contains member. When a router port receives an IGMP general
query message, the Switch 7700 will reset the aging timer of the port. When a
port other than a router port receives the IGMP general query message, the Switch
7700 will notify the multicast router that a port is ready to join a multicast group
and starts the aging timer for the port.
2 IGMP specific query message: Transmitted from the multicast router to the
multicast members and used for querying if a specific group contains any member.
When received IGMP specific query message, the switch only transmits the specific
query message to the IP multicast group which is queried.
3 IGMP report message: Transmitted from the host to the multicast router and used
for applying to a multicast group or responding to the IGMP query message.
When received, the switch checks if the MAC multicast group is ready to join. If
the corresponding MAC multicast group does not exist, the switch notifies the
router that a member is ready to join a multicast group, creates a new MAC
multicast group, adds the port received the message to the group, starts the port
aging timer, and then adds all the router ports in the native VLAN of the port into
the MAC multicast forwarding table. Meanwhile it creates an IP multicast group
and adds the port received to it. If the corresponding MAC multicast group exists
but does not contains the port received the report message, the switch adds the
port into the multicast group and starts the port aging timer. Then the switch
checks if the corresponding IP multicast group exists. If it does not exist, the switch
creates a new IP multicast group and adds the port received the report message to
it. If it does exist, the switch adds the port. If the corresponding MAC multicast
group exists and contains the port, the switch will only reset the aging timer of the
port.
4 IGMP leave message: Transmitted from the multicast group member to the
multicast router to notify that a router host has left the multicast group. The
Switch 7700 transmits the specific query message concerning that group to the
port received the message, in an effort to check if the host still has other members
of this group and starts a maximum response timer. If the switch has not received
any report message from the multicast group, the port will be removed from the
corresponding MAC multicast group. If the MAC multicast group does not have
Internet
A router running
IGMP
An Ethernet switch
running IGMP
snooping
IGMP packets
IGMP packets