FSSO for Windows AD

FSSO for Windows AD

FSSO for Windows AD requires at least one Collector agent. Domain Controller agents may also be required depending on the Collector agent working mode. There are two working modes to monitor user logon activity: DC Agent mode or Polling mode.


Collector agent DC Agent mode versus Polling mode

DC Agent mode                                       Polling Mode

Installation               Complex — Multiple installations: one agent per DC plus Collector agent, requires a reboot

Easy — Only Collector agent installation, no reboot required

Resources                Shares resources with DC system                 Has own resources

Network load            Each DC agent requires minimum 64kpbs bandwidth, adding to network load

Increase polling period during busy period to reduce network load

Level of Con- fidence

Captures all logons                                       Potential to miss a login if polling period is too great


DC Agent mode

DC Agent mode is the standard mode for FSSO. In DC Agent mode, a Fortinet authentication agent is installed on each domain controller. These DC agents monitor user logon events and pass the information to the Collector agent, which stores the information and sends it to the FortiGate unit.

The DC agent installed on the domain controllers is not a service like the Collector agent — it is a DLL file called dcagent.dll and is installed in the Windows\system32 directory. It must be installed on all domain controllers of the domains that are being monitored.


FSSO in DC agent mode

DC Agent mode provides reliable user logon information, however you must install a DC agent on every domain controller. A reboot is needed after the agent is installed. Each installation requires some maintenance as well. For these reasons it may not be possible to use the DC Agent mode.

Each domain controller connection needs a minimum guaranteed 64kpbs bandwidth to ensure proper FSSO functionality. You can optionally configure traffic shapers on the FortiGate unit to ensure this minimum bandwidth is guaranteed for the domain controller connections.

Polling mode

In Polling mode there are three options — NetAPI polling, Event log polling, and Event log using WMI. All share the advantages of being transparent and agentless.

NetAPI polling is used to retrieve server logon sessions. This includes the logon event information for the Controller agent. NetAPI runs faster than Event log polling but it may miss some user logon events under heavy system load. It requires a query round trip time of less than 10 seconds.

Event log polling may run a bit slower, but will not miss events, even when the installation site has many users that require authentication. It does not have the 10 second limit on NetAPI polling. Event log polling requires fast network links. Event log polling is required if there are Mac OS users logging into Windows AD.

Event log using WMI polling: WMI is a Windows API to get system information from a Windows server, CA is a WMI client and sends WMI queries for user logon events to DC, which in this case is a WMI server. Main advantage in this mode is that CA does not need to search security event logs on DC for user logon events, instead, DC returns all requested logon events via WMI. This also reduces network load between CA and DC.

In Polling mode, the Collector agent polls port 445 of each domain controller for user logon information every few seconds and forwards it to the FortiGate unit. There are no DC Agents installed, so the Collector agent polls the domain controllers directly.


FSSO in Polling mode

A major benefit of Polling mode is that no FSSO DC Agents are required. If it is not possible to install FSSO DC Agents on your domain controllers, this is the alternate configuration available to you. Polling mode results in a less complex install, and reduces ongoing maintenance. The minimum permissions required in Polling mode are to read the event log or call NetAPI.


Collector agent AD Access mode – Standard versus Advanced

The Collector agent has two ways to access Active Directory user information. The main difference between Standard and Advanced mode is the naming convention used when referring to username information.

Standard mode uses regular Windows convention: Domain\Username. Advanced mode uses LDAP convention: CN=User, OU=Name, DC=Domain.

If there is no special requirement to use LDAP— best practices suggest you set up FSSO in Standard mode. This mode is easier to set up, and is usually easier to maintain and troubleshoot.

Standard and advanced modes have the same level of functionality with the following exceptions:

  • Users have to create Group filters on the Collector agent. This differs from Advanced mode where Group filters are configured from the FortiGate unit. Fortinet strongly encourages users to create filters from CA.
  • Advanced mode supports nested or inherited groups. This means that users may be a member of multiple monitored groups. Standard mode does not support nested groups so a user must be a direct member of the group being monitored.

One thought on “FSSO for Windows AD

  1. Hildi

    Hi Mike, I usually watch your videos and learn a lot from them, thank You. I wanna ask you something about this topic, In your experience, how many users are too many to use polling mode? for a new deployment you see convenient to use this method? or you recommend agent mode? Thanks a lot for reading


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