3Com S7902E, Configuration Manual

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MLD SSM Mapping
The MLD SSM mapping feature allows you to configure static MLD SSM mappings on the last hop
router to provide SSM support for receiver hosts running MLDv1. The SSM model assumes that the last
hop router is aware of the desired IPv6 multicast sources when receivers join IPv6 multicast groups.
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When a host running MLDv2 joins a multicast group, it can explicitly specify one or more multicast
sources in its MLDv2 report.
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A host running MLDv1, however, cannot specify multicast source addresses in its MLDv1 report. In
this case, you need to configure the MLD SSM mapping feature to translate the (*, G) information in
the MLDv1 report into (G, INCLUDE, (S1, S2...)) information.
Figure 1-5 Network diagram for MLD SSM mapping
MLDv1 report
MLDv2 report
Router A
Querier
Host A (MLDv1)
IPv6 SSM
Receiver
Host B (MLDv1)
Receiver
Host C (MLDv2)
Receiver
As shown in Figure 1-5 , on an IPv6 SSM network, Host A and Host B are running MLDv1 and Host C is
running MLDv2. To provide SSM service for all the hosts while it is infeasible to run MLDv2 on Host A
and Host B, you need to configure the MLD SSM mapping feature on Router A.
With the MLD SSM mapping feature configured, when Router A receives an MLDv1 report, it checks the
IPv6 multicast group address G carried in the message:
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If G is not in the IPv6 SSM group range, Router A cannot provide the SSM service but the ASM
service.
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If G is in the IPv6 SSM group range but no MLD SSM mappings corresponding to the IPv6
multicast group G have been configured on Router A, Router A cannot provide SSM service and
drops the packet.
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If G is in the IPv6 SSM group range, and the MLD SSM mappings have been configured on Router
A for multicast group G, Router A translates the (*, G) information in the MLD report into (G,
INCLUDE, (S1, S2...)) information based on the configured MLD SSM mappings and provides
SSM service accordingly.