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Figure 5.17 – DHCP Boot
5.11
IGMP Snooping
IGMP snooping is used to establish the multicast groups to forward multicast packets to
member ports. IGMP snooping avoids wasting the bandwidth while IP multicast packets are
running over the network. A switch that does not support IGMP snooping cannot tell a multicast
packet from broadcast packet, so it treats them as broadcast packets. Without IGMP snooping,
the multicast packet forwarding function is no different from broadcast packets.
A switch with IGMP snooping supports 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 had joined a specified IP multicast group.
Multicast packets will be discarded by IGMP Snooping if the user transmits multicast packets to
the multicast group which has not been set-up in advance.
Waters Network Systems
2800M/MR User's Manual
Page 50
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