Multicast PIM: Why does AutoRP in Sparse mode work with Listner disabled?

Question

Cisco

According to various sources, in order to make Auto-RP work in sparse mode, one must either statically specify the RP that will be used for Auto-RP multicast groups, or use the ip pim autorp listener command, which turns on PIM-Dense mode for Auto-RP multicast − 224.0.1.39 and 224.0.1.40. In practice, it turns out that Auto-RP works even without these conditions, i.e. with the listener turned off and without static RP configuration. At the same time, the D flag is set for Auto-RP multicast routes, which means that the PIM-Dense protocol is used. It seems that PIM-dense is always enabled for groups 224.0.1.39 and 224.0.1.40, regardless of the activation state of the listener parameter. Is this true or am I not understanding something?

Answer 1

And what is the configuration? The behavior looks suspiciously like "ip pim sparse-dense".
Well, nowhere without a model of a piece of iron and a version of its software ...