IGMPv2 and 3 interoperability for SSM

[horus66]

If I have a layer 3 switch acting as my PIM enabled multicast router for SSM multicast, with a directly connected downstream layer 2 switch also supporting IGMPv3 and I plug in a device such as a Cisco phone that only supports IGMPv2, can I still make SSM work by configuring IGMP Querior on my layer 3 Multicast router/switch to translate between IGMPv2 and v3?

[M02@rt37]

Hello @horus66 

I dont think so. For SSM to work properly, IGMPv3 is required because it allows receivers to specify the source of the multicast traffic. IGMPv2 does not have the capability to specify a source.

So, configuring an IGMP Querier on your L3 switch will not translate IGMPv2 membership reports to IGMPv3. IGMP Querier election simply ensure that there is an active IGMP querier on the L2 network to handle membership queries ;  but it doesn't provide IGMP version translation.

[Harold Ritter]

Hi @horus66 ,

You could use the SSM mapping feature to map IGMPv2 groups to a source address.

https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipmulti_igmp/configuration/xe-16/imc-igmp-xe-16-book/imc-ssm-map.html#GUID-A929E8CF-6DE9-45A5-9CDD-81026E2AB4BE

Regards,

[vishalbhandari]

@horus66 No, IGMP Querier cannot translate between IGMPv2 and IGMPv3. In Source-Specific Multicast (SSM), IGMPv3 is required because it allows receivers to specify the exact source IP they want to receive traffic from. IGMPv2 does not support source filtering—it only allows group membership reports. If your Cisco phone only supports IGMPv2, it won't be able to request traffic from a specific source, which is essential for SSM to function. You would need an intermediate mechanism, such as an IGMP proxy or a multicast middleware solution, to bridge the gap, but simply enabling an IGMP Querier on the Layer 3 switch won’t resolve this limitation.

[Harold Ritter]

Hi @vishalbhandari ,

It is indeed possible to map IGMPv2 groups to a specific source for IGMPv2 to interoperate with SSM. This is what the SSM mapping feature is all about. Please refer to the document I posted about this feature in an earlier response to the OP.

Regards,