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.
Alternativelly 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 droped.
