Currently zabbix agent supports agent autoregistration and discovery from zabbix server. First requires adding server address into agent config. Second requires configuration in zabbix server.
But agent can find server via DNS record. For example, jabber client tries to find server address via DNS SRV query:
> _xmpp-client._tcp.example.net. IN SRV 5 0 5222 server.example.net.
Zabbix agent could try to query something like that for zabbix server. For example agent could query:
> _zabbix-agent._tcp.example.net. IN SRV 5 0 10051 zabbix.example.net.
Domain can be taken from hostname of the server with zabbix agent
Such configuration with agent autoregistration can make fully automated agent registration