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DES-7200 Configuration Guide Chapter 3 IGMP
Configuration
3-3
the group address. On the other hand, the host running the IGMP V3 notifies this
host the desired multicast group to join, and also the addresses of the multicast
sources to receive. The host can indicate that it wants to receive multicast traffic
from which sources through an inclusion list or an exclusion list. At the same time,
another benefit of the IGMP v3 is that it saves bandwidth to avoid unnecessary,
invalid multicast data traffics from occupying network bandwidth. It is particularly
useful in the case where multiple multicast sources share one multicast address.
The IGMPv1 and IGMPv2 can also implement “source address filter” in some
sense, which, however, is performed on the end of receiving the multicast traffic.
As shown in the following diagram, there are two multicast sources (S1 and S2),
which send the data traffic of the same multicast address (G). The multicast flow
of S1 and S2 will be sent to all hosts receiving flows from G. If host A only wants to
receive multicast flows from S1, it filters flows by using the related client software.
Figure 1-2 Multicast route forwarding without filtering source
If the equipments in the network support IGMP v3, host A wants to receive the
traffic from S1 only. It can send the IGMPv3 packet of join G include S1. If host B
wants to receive the traffic from S2 only, it can send the IGMPv3 packet of join G
include S2. Therefore, the traffics are forwarded as shown in the following
diagram. This saves bandwidth.
Figure 1-3 Multicast route forwarding with filtering source
In contrast to Version 2, Version 3 defines the following two kinds of messages:
Membership Query
Version 3 Membership Report
There are three types of Membership Query:
General Query: Used to query all the multicast members under the interface.
Group-Specific Query: Used to query the members of the specified group
under the interface.
Group-and source-Specific Query: This type is the new one in the IGMPv3,
which is used to query if any member under the interface needs to receive
the multicast traffic of the particular group from the sources in the specified
source list.
Different from the Membership Report in IGMP Version2, the Membership Report
in the IGMP Version3 always has the destination address of 224.0.0.22. The
Membership Report packets in IGMP Version3 include the information of multiple