PIM multicast routing

[cisco2003]

I have a cisco router 3640 connected to the multicast server through e0/0 and connected client through e0/1,

I enable multicast routing on the router and plan to run PIM dense mode. If I enable ip pim dense-mode on both of the interfaces, client can get multicast, but if I do not run PIM on e0/1, or e0/0, client can not get multicast, why does it work like that? As I know , PIM is a protocol running between two PIM routers.

[Richard Burts]

While it is true that PIM is a routing protocol for propagating multicast information, configuring PIM on the interface does more than just enable forwarding of PIM updates. Enabling PIM on the interface also enables building the multicast forwarding tree which the router uses to enable forwarding of multicast packets.

Without multicast forwarding enabled any multicast packet is treated as being local to that segment. So the client can not receive from the multicast source unless both interfaces are activated for forwarding multicast.

HTH

Rick