Hi !
1. the 232.x.x.x group per default is reserved for SSM ( source-specific multicast)
this can be changed on the RP
2. if the receiver do not send the source-address in the IGMP joins you can either change mode to ASM or use SSM-map to define the source-address for that groups
3. or change the address to another one like 239.x.x.x
on the last hop router do a "monitor traffic interface xxx protocol IGMP extensive no-resolve" to see the IGMP joins from the receiver
regards
alexander
