Help us improve your experience.

Let us know what you think.

Do you have time for a two-minute survey?

Understanding Integrated User Firewall Domain PC Probing


Overview of Domain PC Probing

At a high level, the integrated user firewall feature gathers IP address, user, and group information from Windows Active Directory domain controller event logs and LDAP services. This information is used to generate Active Directory authentication table entries on an NFX Series device. Authentication entries serve as the authentication source for security policies that enforce user-based or group-based access control.

PC probing acts as a supplement of event log reading. When a user logs in to the domain, the event log contains that information. The PC probe is triggered only when there is no IP-to-address mapping from the event log.

Domain information constantly changes as users log in and out of domain PCs. The integrated user firewall probe functionality provides a mechanism for tracking and verifying information in the authentication tables by directly probing domain PCs for IP address-to-user mapping information. New and changed information identified by the probe serves to update Active Directory authentication table entries, which is critical to maintaining firewall integrity.

The IP address filter also impacts the PC probe. Once you configure the IP address filter, only the IP address specified in the filter is probed.

Probing Domain PCs for User Information

The integrated user firewall feature tracks the online status of users by probing domain PCs. If a user is not online or is not an expected user, the Active Directory authentication table is updated as appropriate. The following probe behaviors apply:

On-demand probingOn-demand probing occurs when a packet is dropped due to a missing entry in the Active Directory authentication table. In this case, an entry is added in pending state to the authentication table, and the domain PC identified by the source IP field of the dropped packet is probed for IP address and user information. The entry remains in pending state until a response is received from the probe.
Manual probingManual probing is used to verify and troubleshoot the online status of a user or a range of users, and is at the discretion of the system administrator. To initiate a manual probe, use the request services user-identification active-directory-access ip-user-probe address ip-address address domain domain-name command. If a domain name is not specified, the probe looks at the first configured domain for the IP address. To specify a range, use the appropriate network address.

Manual probing can cause entries to be removed from the Active Directory authentication table. For example, if there is no response from your PC due to a network issue, such as when the PC is too busy, the IP address entry of the PC is marked as invalid and your access is blocked.

If the device cannot access a domain PC for some reason, such as a network configuration or Windows firewall issue, the probe fails.

Probe Response

Based on the domain PC probe response, updates are made to the Active Directory authentication table, and associated firewall policies take effect. If no response is received from the probe after 90 seconds, the authentication entry times out. The timed-out authentication entry is the pending state authentication entry, which is generated when you start the PC probe.

If the probe is successful, the state of the authentication entry is updated from pending to valid. If the probe is unsuccessful, the state of the authentication entry is marked as invalid. The invalid entry has the same lifetime as a valid entry and is overwritten by upcoming fwauth (firewall authentication process) authentication results or by the event log. Table 1 lists probe responses and corresponding authentication table actions.

Table 1: Probe Responses and Associated Active Directory Authentication Table Actions

Probe Response from Domain PC

Active Directory Authentication Table Action

Valid IP address and username

Add IP-related entry.

Logged on user changed

Update IP-related entry.

Connection timeout

Update IP-related entry as invalid.

Access denied

Update IP-related entry as invalid.

Connection refused

Update IP-related entry as invalid.

Authentication failed

(The configured username and password have no privilege to probe the domain PC.)

Update IP-related entry as invalid.

Probe Configuration

On-demand probing is enabled by default. To disable on-demand probing, use the set services user-identification active-directory-access no-on-demand-probe statement. Delete this statement to reenable probing. When on-demand probing is disabled, manual probing is available.

The probe timeout value is configurable. The default timeout is 10 seconds. To configure the timeout value, use the following statement:

If no response is received from the domain PC within the wmi-timeout interval, the probe fails and the system either creates an invalid authentication entry or updates the existing authentication entry as invalid. If an authentication table entry already exists for the probed IP address, and no response is received from the domain PC within the wmi-timeout interval, the probe fails and that entry is deleted from the table.


To probe domain PCs, you must configure the integrated user firewall feature with the username and password credentials. You do not necessarily need a username and password account for each PC; instead you could set up one administrator account with privileges to access information on multiple PCs.

Probe Rate and Statistics

The maximum probe rate for the integrated user firewall feature is set by default and cannot be changed. Probe functionality supports 5000 users, or up to 10 percent of the total supported authentication entries, whichever is smaller. Supporting 10 percent means that at any time, the number of IP addresses waiting to be probed cannot exceed 10 percent. For more information about the number of supported Active Directory authentication table entries, see Active Directory Authentication Tables.

High-level statistics covering probe activity are available for the total number of probes and the number of failed probes. Table 1 describes the reasons for probe failures. To display probe statistics, use the show services user-identification active-directory-access statistics ip-user-probe command.