Could anyone explain the need/purpose of the ip pim passive command? Is it solely for last hop routers (LHRs)? Should/could this be applied to First Hop Routers (FHRs) too?
This is from Cisco website
If the ip pim passive command is configured on an interface enabled for IP multicast, the device will operate this interface in PIM passive mode, which means that the device will not send PIM messages on the interface nor will it accept PIM messages from other devices across this interface. The device will instead consider that it is the only PIM device on the network and thus act as the DR and also as the DF for all bidir-PIM group ranges. IGMP operations are unaffected by this command.
Note Do not use this command on LANs that have more than one multicast device connected to them because all devices with this command configured will consider themselves to be DR/DF, resulting in duplicate traffic (PIM-SM, PIM-DM, PIM-SSM) or even in looping traffic (bidir-PIM).