Today Zabbix has serious problems to identify/distinguish hosts:

• local and remote host names or domain names might not match
• the IP address might have been reused
• a host is moved from one network to another (e.g. from the LAN to a road warrior cafe)
• a host might have several network interfaces
• an IPv6 network with a /48 prefix is way too large to run a discovery looping over all IP addresses
  Instead of fragile host name/IP address constructs I would suggest to bind each agent to a UUID. It should be defined by the agent once, it should never change, and it must not be shared. It should be part of the active and passive communication between agent, proxy and server. It should be accepted or denied by the server, depending upon additional information provided by the agent (PSK, IP address, approved by a human Zabbix administrator, etc.)