Multicast - Understanding global vs interface-level configuration
When configuring Multicast, the ip pim sparse-mode or the ip pim dense-mode interface configuration mode commands enable multicast routing on a specific interface. While this allows the interface to participate in multicast routing, it does not enable multicast routing globally on the router. Without the global ip multicast-routing command, the router will not route multicast traffic beyond the configured interface.
In a lab environment with a single router, IGMP can function on a multicast-enabled interface without global multicast routing enabled. However, for multicast routing across multiple routers, the ip multicast-routing command is necessary.
Links:
https://forum.networklessons.com/t/igmp-version-1/1319/38?u=lagapidis
https://networklessons.com/multicast/multicast-routing
https://networklessons.com/multicast/multicast-pim-dense-mode
https://networklessons.com/multicast/multicast-pim-sparse-mode