By default, XMPP uses brokers, or XMPP servers, to relay communication between entities in the network. XMPP can work in a server-less mode as well, but the default mode of operation is for entities to connect to a broker. As we have seen in earlier chapters, a broker provides a lot of features to the network that are very valuable, especially for the IoT.

One such feature makes the network topology independent, or more topology independent. Since clients in the network connect to brokers, they can all reside behind separate firewalls and still communicate with each other. This is also a security feature since connections are outbound. Firewalls can block incoming connections without preventing clients inside the firewalls from communicating with each other.