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Manage Event logs to Generate IP Address-to-User Mapping

 

SRX Series and NFX Series device gathers IP address, user, and group information from Windows Active Directory domain controller event logs and adds to the active directory authentication table. Authentication entries become a source for authentication.

Understanding How the WMIC Reads the Event Log on the Domain Controller

This topic includes the following sections:

Windows Management Instrumentation Client

When you configure the integrated user firewall feature on a device, the device establishes a Windows Management Instrumentation (WMI)/Distributed Component Object Module (DCOM) connection to the domain controller. The device acts as a WMI client (WMIC). It reads and monitors the security event log on the domain controller. The device analyzes the event messages to generate IP address-to-user mapping information.

All configuration regarding the WMIC is optional; it will function with default values. After the domain is configured (by the set services user-identification active-directory-access domain statement), the WMIC starts to work. The WMIC connection to the domain controller uses the same user credentials as those configured for the domain.

Caution

Integrated user firewall uses NTLMv2 as the default WMIC authentication protocol for security reasons. NTLMv1 exposes the system to attacks in which authentication hashes could be extracted from NTLMv1 authentication responses.

For compatibility with integrated user firewall, you must apply the latest version of the Microsoft SP2 patch if you are running an older version of Windows OS, including Windows 2000, Windows XP, and Windows 2003.

WMIC Reads the Event Log on the Domain Controller

The following behaviors apply to reading the event log:

  • The device monitors the event log at a configurable interval, which defaults to 10 seconds.

  • The device reads the event log for a certain timespan, which you can configure. The default timespan is one hour. Each time at WMIC startup, the device checks the last timestamp and the timespan. If the last timestamp is older than the current timespan, then the timespan takes effect. After the WMIC and the UserID process start working, the timespan does not apply; the device simply reads the latest event log.

  • The device can read the event log to obtain IPv6 addresses in addition to IPv4 addresses.

  • During WMIC startup, the device has a maximum count of events it will read from the event log, and that maximum is not configurable.

    • On SRX300, SRX320, SRX340, and SRX345 devices, the maximum count is 100,000.

    • On SRX5400, SRX5600, and SRX5800 devices, the maximum count is 200,000.

    During WMIC startup, this maximum count is used with the timespan setting, so that if either limit is reached, the WMIC stops reading the event log.

  • After a failover, the device reads the event log from the latest event log timestamp.

  • In a chassis cluster environment, the WMIC works on the primary node only.

Specifying IP Filters to Limit IP-to-User Mapping

You can specify IP filters to limit the IP address-to-user mapping information that the device generates from the event log.

To understand when a filter is useful for such mapping, consider the following scenario. A customer deploys 10 devices in one domain, and each device controls a branch. All 10 devices read all 10 branch user login event logs in the domain controller. However, the device is configured to detect only whether the user is authenticated on the branch it controls. By configuring an IP filter on the device, the device reads only the IP event log under its control.

You can configure a filter to include or exclude IP addresses or prefixes. You can specify a maximum of 20 addresses for each filter.

Event Log Verification and Statistics

You can verify that the authentication table is getting IP address and user information by issuing the show services user-identification active-directory-access active-directory-authentication-table all command. A list of IP address-to-user mappings is displayed for each domain. The table contains no group information until LDAP is running.

You can see statistics about reading the event log by issuing the show services user-identification active-directory-access ip-user-mapping statistics domain command.

Using Firewall Authentication as an Alternative to WMIC

This topic includes the following sections:

WMIC Limitations

The primary method for the integrated user firewall feature to get IP address-to-user mapping information is for the device to act as a WMI client (WMIC). However, the WMIC has limitations, such as the following:

  • On Windows XP or Server2003, the Windows firewall does not allow the WMIC request to pass through because of the dynamic port allocation of the Distributed Component Object Model (DCOM). Therefore, for these operating systems when Windows firewall is enabled, the PC does not respond to the WMIC probe.

  • Because the event-log-reading and PC probe functions both use WMI, using a global policy to disable the WMI-to-PC probe also affects event log reading.

Because these cases might result in the failure of the PC probe, a backup method for getting IP address-to-user mappings is needed. That method is to use firewall authentication to identify users.

Firewall Authentication as a Backup Method for IP Address-to-User Mappings

If you want to use firewall authentication to identify users for the integrated user firewall feature, specify a domain name in the set security policies from-zone trust to-zone untrust policy <policy-name> then permit firewall-authentication user-firewall domain <domain-name> statement.

If a domain is configured in that statement, fwauth recognizes that the domain is for a domain authentication entry, and will send the domain name to the fwauth process along with the authentication request. After it receives the authentication response, fwauth deletes that domain authentication entry. The fwauth process sends the source IP address, username, domain, and other information to the USERID process, which verifies that it is a valid domain user entry. The subsequent traffic will hit this user firewall entry.

Note

The Active Directory authentication entry that comes from the fwauth process is not subject to the IP filters.

Understanding Integrated User Firewall Domain PC Probing

This topic includes the following sections:

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 a 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.
Note

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.

Note

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. For SRX 5400, SRX 5600, and SRX 5800 devices, the probe rate is 600 times per minute. For branch SRX Series devices, the probe rate is 100 times per minute. 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 Understanding 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.