Why is a redundant PIM stub router topology a bad network design decision?

Convergence time is not inherently longer in a redundant stub topology; the speed of multicast convergence is governed by upstream PIM timers and IGMP leave latency, neither of which is worsened by having two stub routers.

PIM stub routers do not participate in full PIM neighbor relationships or the Assert process used to elect a single designated forwarder on a shared segment. When two stub routers are redundantly connected to the same downstream network, both independently receive multicast traffic from upstream and forward it, delivering duplicate streams to receivers and making this a fundamentally flawed design for any segment with active multicast receivers.

PIM stub routing operates at Layer 3 and does not interact with IGMP snooping, which is a Layer 2 switch function that inspects IGMP messages to limit multicast flooding within a VLAN.

PIM stub mode on a router does not interfere with PIM snooping on a switch; PIM snooping passively listens to PIM messages to build forwarding state and is unaffected by the stub designation of an adjacent router.