All communication between your Orion server or additional poller engine and the agent is initiated by the agent, and your Orion server does not initiate communication with the agent. You do not need to have a direct route from the Orion server or additional poller to the host where the agent is installed. To use this communication method, port 17778 must be open on the Orion server firewall to receive information from the agent.
This communication method is most useful when the agent is installed on a network separated from your Orion server by one or more NAT devices, and you have no easy way to connect the two.
This communication method is also known as an active agent. In active mode, there are no listening ports on the agent.
For more information on other communication modes, see Server-initiated communication.