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3-15. IGMP
IGMP is used to establish the multicast groups to forward the multicast
packet to the member ports, and in nature, avoids wasting the bandwidth while IP
multicast packets are running over the network. This is because a switch not
supporting IGMP can not tell the multicast packet from the broadcast packet, so it
can only treat them all as the broadcast packet. Without IGMP, the multicast packet
forwarding function is plain and nothing the same as broadcast packet.
A switch supporting IGMP Proxy with the functions of query, report and leave,
a type of packet exchanged between IP Multicast Router/Switch and IP Multicast
Host, can update the information of the Multicast table when a member (port) joins
or leaves an IP Multicast Destination Address. With this function, once a switch
receives an IP multicast packet, it will forward the packet to the members who
joined in a specified IP multicast group before.
IGMP Snooping is included in IGMP Proxy, but IGMP Proxy terminates the
IGMP packets from multicast users and requests upper-level network equipment for
multicast recourses as a proxy of the multicast user.
3-15-1 Proxy
Function name:
IGMP Proxy Configuration
Function description:
IGMP proxy enables the switch to issue IGMP host messages on behalf of
hosts that the system discovered through standard IGMP interfaces. The
switch acts as a proxy for its hosts.
You enable IGMP proxy on the switch, which connects to a router closer to the
root of the tree. This interface is the upstream interface. The router on the
upstream interface should be running IGMP.
Fig. 3-163 IGMP Proxy
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