Discovery refers to either a client (producer or consumer) establishing a 'transport connector' to the broker or a broker establishing 'network connector' to another broker without explicit static configuration of broker (IP or hostname).
The scheme 'multicast' refers to either listening for or advertising discovery events on a multicast address. zeroconf is similar to multicast, except for protocol specific to Apple's Rendezvous (bonjour).
The above configuration in the broker xml file will make it automatically establish network connectors to other brokers that advertise themselves on the multicast address: when this broker gets a discovery event from another broker, the event has information that enables it to establish network connector to that broker.
Self-advertisement is facilitated by the following config:
An example usage of discovery on the client side (using the transport 'discovery' that uses discovery agent) ...
ps: discovery (which is a confusing name) is just like a 'reliable' transport such as failover. If it is unable to connect to a broker, it will try another broker (assuming it