When a candidate rendezvous point (C-RP) is configured on an interface, the C-RP periodically sends Advertisement messages to a bootstrap router (BSR). The Advertisement messages carry the C-RP priority and the holdtime of Advertisement messages. After receiving Advertisement messages, the BSR starts the C-RP timeout timer. The timer value is set to the holdtime of Advertisement messages. Before the timer expires, the BSR collects the C-RP information in Advertisement messages into an RP-set, encapsulates the RP-set into a Bootstrap message, and advertises the Bootstrap message to all PIM devices in the PIM domain. If the BSR does not receive any Advertisement message from the C-RP after the timer expires, the BSR considers the C-RP invalid or unreachable on the network. The interval for sending Advertisement messages must be smaller than the holdtime of Advertisement messages.
You can manually configure the interval for sending Advertisement messages, C-RP priority and holdtime of Advertisement messages. To prevent C-RP spoofing, set the range of valid C-RP addresses on the BSR. Then the BSR accepts only the Advertisement messages with source addresses in the specified range.