316 CHAPTER 18: MULTICAST PROTOCOL

Figure82 Implementing IGMP Snooping

Table309 explains IGMP Snooping terminology.

Table309 IGMP Snooping Terminology

Term Meaning
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 5500 will reset the aging
timer of the port. When a port other than a router port receives
the IGMP general query message, the Switch 5500 will notify
the multicast router that a port is ready to join a multicast group
and starts the aging timer for the port.
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.
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 that 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 contain the port that
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 that 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.
Internet
IGMP packets
A Ethernet Switch
running IGMP Snooping
A router
running IG MP
IGMP pack e ts
Switch 5500 running
IGMP Snooping