I'm using Mqtt and I need that client device on the same local wifi network can search and automatically connect to a broker/server without know his IP address (that change everytime), searching in the local network, is it possible ? how ?
Why does it change? You can setup your network (the Server) to use always the same adress (set it fix instead of using DHCP).
You also can setup a small server-app (B4J) which scans the local network to find the MQTT Server and on request you send the actual IP of the mqtt server...