PING

The PING layer is responsible for finding the initial membership of a group. It does so upon reception of a FIND_INITIAL_MBRS event (sent by the GMS layer). When done, a FIN_INITIAL_MBRS_OK event is sent up the stack, containing the members found as argument. GMS waits until it receives the initial membership, and - based on it - determines the current coordinator to which it then sends a join request. When not receiving the initial members within a certain time frame, a timeout is received, and the GMS creates a singleton group (with itself as only member).

Currently the initial membership is found either using a multicast to an IP multicast address to which all members respond, or using the Router daemon (see 3.8.1), if IP multicast is not enabled.