Information Technology Reference
In-Depth Information
Version 2 membership report:
A message sent to the group address with the mul-
ticast group members (IP addresses). It is sent to by hosts to join and remain in multi-
cast groups on the segment.
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Version 2 leave group:
Sent by the hosts to indicate that a host will leave a group; it
is sent to destination 224.0.0.2. After the host sends the leave group message, the
router responds with a group-specific query.
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Version 1 membership report:
For backward compatibilit y w ith IGMP v1 hosts.
Yo u enable IGMP on an interface when you configure a multicast routing protocol, such
as PIM. You can configure the interface for IGMPv1, IGMPv2, or IGMPv3.
IGMPv3
IGMPv3 provides the extensions required to support source-specific multicast (SSM). It is
designed to be backward compatible with both earlier versions of IGMP.
IGMPv3 has two message types, plus three for backward compatibility:
Membership query:
Sent by the router to check that a host wants to join a group.
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Version 3 membership report:
A message sent to the group address with the mul-
ticast group members (IP addresses). It is sent by hosts to request and remain in multi-
cast groups on the segment.
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Version 2 membership report:
A message sent to the group address with the mul-
ticast group members (IP addresses). It is sent by hosts to request and remain in multi-
cast groups on the segment. This message is used for backward compatibility with
IGMPv2 hosts.
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Version 2 leave group:
Sent by the hosts to indicate that a host will leave a group,
to destination 224.0.0.2. The message is sent without having to wait for the IGMPv2
membership report message. This message is used for backward compatibility with
IGMPv2 hosts.
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Version 1 membership report:
A message used for backward compatibility with
IGMPv1 hosts.
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Yo u e n a b l e I G M P o n a n i n t e r f a c e w h e n y o u e n a b l e a m u l t i c a s t r o u t i n g p r o t o c o l , s u c h a s
PIM. You can configure the interface for IGMPv1, IGMPv2, or IGMPv3.
CGMP
CGMP is a Cisco proprietary protocol implemented to control multicast traffic at Layer 2.
Because a Layer 2 switch is unaware of Layer 3 IGMP messages, it cannot keep multicast
packets from being sent to all ports.
As shown in Figure 11-25, with CGMP the LAN switch can speak with the IGMP router
to find out the MAC addresses of the hosts that want to receive the multicast packets.
With CGMP, switches distribute multicast sessions only to the switch ports that have
group members.
