Administer > Monitor your network > Monitor devices with SolarWinds Orion agents > Agent communication modes

Agent communication modes

Communication modes determine how the agent and the Orion server communicate. This is frequently influenced by where the device you want to monitor is on your network.

Server-initiated communication

This communication method is also known as a passive agent.

Any communication between your Orion server or additional polling engines and the agent is initiated by the Orion server itself. To allow communication from the Orion server, the firewall service running on the monitored device or the network firewall must allow incoming connections through port 17790. If the agent is configured to use another port, update the firewall rules to allow incoming connections from the other port.

Agent-initiated communication

This communication method is also known as an active agent. In active mode, there are no listening ports on the agent.

Any communication between your Orion server or additional polling engines and the agent service is initiated by the agent service itself. Update your firewall rules to allow outgoing connections through port 17778 to enable communication between the agent and the Orion server. Open port 17791 if the agent is on Windows 2008 R2.

You cannot use agent-initiated communication through a proxy using NTLM authentication if the agent is running on a Linux-based device.

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.