H3C Technologies H3C S10500 Series Switches - Manual (Page 117)

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• If G is not in the SSM group range, Router A cannot provide the SSM service but can provide the
ASM service.
• If G is in the SSM group range but no IGMP SSM mappings that correspond to the multicast group
G have been configured on Router A, Router A cannot provide SSM service and drops the message.
• If G is in the SSM group range and the IGMP SSM mappings have been configured on Router A for
multicast group G, Router A translates the (*, G) information in the IGMP report into (G, INCLUDE,
(S1, S2...)) information based on the configured IGMP SSM mappings and provides SSM service
accordingly.
NOTE:
•
The IGMP SSM mapping feature does not process IGMPv3 reports.
• For more information about the SSM group range, see the chapter “PIM configuration.”
IGMP proxying
In some simple tree-shaped topologies, it is not necessary to configure complex multicast routing
protocols, such as PIM, on the boundary devices. Instead, you can configure IGMP proxying on these
devices. With IGMP proxying configured, the device serves as a proxy for the downstream hosts to send
IGMP messages, maintain group memberships, and implement multicast forwarding based on the
memberships. In this case, each boundary device is a host but no longer a PIM neighbor to the upstream
device.
Figure 36 Network diagram for IGMP proxying
Query from Router A
Report from Router B
Ethernet
Router interface
Host interface
Proxy & Querier
Router B
Querier
Router A
Host B
Receiver
Host A
Receiver
Host C
Query from Router B
Report from Host
PIM domain
As shown in Figure 36 , the following types of interfaces are defined on an IGMP proxy device:
• Upstream interface—Also called the “proxy interface”. A proxy interface is an interface on which
IGMP proxying is configured. It is in the direction toward the root of the multicast forwarding tree.
An upstream interface acts as a host that is running IGMP. Therefore, it is also called the “host
interface”.
• Downstream interface—An interface that is running IGMP and is not in the direction toward the root
of the multicast forwarding tree. A downstream interface acts as a router that is running IGMP.
Therefore, it is also called the “router interface”.