By the means of a DHIS client a host which is assigned a dynamic IP address (either from its ISP or from DHCP) is able to communicate with a DHIS server in order to advertise its newly acquired IP address. The DHIS server (permanently online) listens to UDP messages from its clients and authenticates these against its knowledge of keys. When authentication is successful the DHIS server updates one or more databases with the newly received IP address for the given client. The server then keeps sending, every period of time, check requests to each of its connected clients. These need to be acknowledged. If not the server will consider, on an individual basis, that the client has disconnected and will again update the databases to an offline state. Alternatively the server may receive an OFFLINE_REQ packet from the client, in which case the DNS record is updated at once and the online state dropped. see ${PREFIX}/share/doc/dhisd/README for info.