I am wondering for the udp multicast to work, router must support it?
Multicast is based on dynamically generated trees that can (theoretically) span the entire internet. These multicast trees are based on two protocols:
- IGMP: Internet Group Management Protocol. Used by receivers and users like me and you.
- PIM: Protocol Independent Multicast. Used by routers to replicate and reroute the packets accordingly.
The client needs to be IGMP-compatible, and the routers need to be PIM-compatible.
To be precise, you will need a multicast router if you want the traffic to traverse different subnets. Normally you can expect multicast to work fine on your local subnet.
Side note, many layer 2-3 switches do not include multicast routing functionality, they can however forward to an external multicast router. Multicast routing can be enabled in CISCO routers, etc.
来源：https://stackoverflow.com/questions/1801621/in-order-for-udp-multicast-to-work-router-must-support-it