Only agents which are on the immediate network subnet are detected automatically by SilkPerformer. All other agents must be added to the Agent Pool by "Add WAN agent".
You can use TRACERT to identify which agent machines are LAN agents and which are WAN agents.
To do so open a command prompt and type:
tracert
If this displays more than one hop then the machine is considered a WAN agent.
If this displays as 1 hop then please check how many NIC"s you have installed on the agent.
This can also happen if communication is blocked by Firewall software on the agent machine. Please ensure to disable any firewalls (including Windows Firewall) or configure exceptions as detailed in Which ports need to be opened in a firewall for SilkPerformer to connect to an agent