Hello Abhishek!
The main purpose of the multicast-routing distributed command is to take advantage of the Multicast Distributed Switching (MDS) functionality that is available on high end Cisco L3 switching devices. MDS is accomplished using a forwarding data structure called a Multicast Forwarding Information Base (MFIB), which is a subset of the routing table. The multicast-routing distributed command essentially enables multicast routing on an L3 device. There is no alternative multicast-routing command. Counterintuativly, the distributedkey word indicates that distributed SWITCHING be taken advantage of in the multicast routing process.
As for stackable switches, there is no specific configuration considerations when configuring multicast routing. The only thing that should be taken into account is the fact that it is the master switch that performs the following in multicast routing:
•It is responsible for completing the IP multicast routing functions of the stack. It fully initializes and runs the IP multicast routing protocols.
•It builds and maintains the multicast routing table for the entire stack.
•It is responsible for distributing the multicast routing table to all stack members.
The stack members perform these functions:
•They act as multicast routing standby devices and are ready to take over if there is a stack master failure. If the stack master fails, all stack members delete their multicast routing tables. The newly elected stack master starts building the routing tables and distributes them to the stack members.
•They do not build multicast routing tables. Instead, they use the multicast routing table that is distributed by the stack master.
For more information about distributed switching and multicast routing using stacked L3 switches, take a look at the following Cisco support document:
I hope this has been helpful!
Laz