IGMP SSM mapping

An IGMPv3 host can explicitly specify multicast sources in its IGMPv3 reports. From the reports, the IGMP router can obtain the multicast source addresses and directly provide the SSM service. However, an IGMPv1 or IGMPv2 host cannot specify multicast sources in its IGMPv1 or IGMPv2 reports.

The IGMP SSM mapping feature enables the IGMP router to provide SSM support for IGMPv1 or IGMPv2 hosts. The router translates (*, G) in IGMPv1 or IGMPv2 reports into (G, INCLUDE, (S1, S2...)) based on the configured IGMP SSM mappings.

As shown in Figure 33, on an SSM network, Host A, Host B, and Host C run IGMPv1, IGMPv2, and IGMPv3, respectively. To provide the SSM service for Host A and Host B, you must configure the IGMP SSM mapping feature on Router A.

After IGMP SSM mappings are configured, Router A checks the multicast group address G in the received IGMPv1 or IGMPv2 report, and performs the following operations:

• If G is not in the SSM group range, Router A provides the ASM service.

• If G is in the SSM group range but does not match any IGMP SSM mapping, Router A drops the report.

• If G is in the SSM group range and matches IGMP SSM mappings, Router A translates (*, G) in the report into (G, INCLUDE, (S1, S2...)) to provide SSM services.

	NOTE: The IGMP SSM mapping feature does not process IGMPv3 reports.

For more information about SSM group ranges, see "Configuring PIM."