The basic difference between agent and agentless is as follows: User-id agent installs on a windows computer and collects the user to ip mappings for forwarding to the firewall Agentless user-id runs on the firewall and queries the windows servers to retrieve the user to ip mapping information User-id agent can install multiple ways Install directly on the domain controller for each one and collect local data Install on one computer and query data from multiple domain controllers from this location General considerations: each domain controller in your AD domain has local only copies of the login mappings you need so all must participate in user-id in some way If you have a lot of processing on the firewall and a lot of domain controllers then agentless user-id may not be practical If your AD computers are spread around multiple WAN links the traffic generated by agentless user-id may be problematic the best source for the gory details is the User-id Best practices documentation. User-ID Best Practices - PAN-OS 5.0, 6.0
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