Supported Platforms
Understanding Active Directory Authentication Tables
This topic includes the following sections:
Active Directory Authentication as an Authentication Source
On an SRX Series device, user information tables serve as the authentication source for information required by firewall security policies. The SRX Series device supports various user information tables including local, user firewall, and Unified Access Control (UAC) types. The integrated user firewall feature introduces another type of authentication source—Active Directory authentication.
The integrated user firewall feature gathers user and group information for Active Directory authentication by reading domain controller event logs, probing domain PCs, and querying Lightweight Directory Access Protocol (LDAP) services within the configured Windows domain. Up to two Windows domains are supported.
From the user and group information, the integrated user firewall feature generates an Active Directory authentication table on the Routing Engine of the SRX Series device, which then pushes the authentication table to the Packet Forwarding Engine. Security policies use the information in the table to authenticate users and to provide access control for traffic through the firewall.
Active Directory Authentication Tables
The Active Directory authentication table contains the IP address, username, and group mapping information that serves as the authentication source for the SRX Series integrated user firewall feature. Information in the table is obtained by reading Window Active Directory domain controller event logs, probing domain PCs, and querying LDAP services within a specified Windows domain.
Reading domain controller event logs generates a list of IP address-to-user mapping information that is used to create entries in the Active Directory authentication table. Once entries have been added in the table, a query is sent to the LDAP server for user-to-group mapping information.
The LDAP server returns all group information; this includes not only information about the groups you directly belong to, but also all the parent (and parent of the parent and so on) groups that you belong to. Group information returned from the LDAP server is compared with the source identity in security policies. If there is a match, Active Directory authentication table entries are updated to include only the group information provided in the security policy. In this way, only relevant group information is listed in the authentication table. Whenever source identity is updated, the authentication table is also updated to reflect the up-to-date relevant group information for all listed users.
When user traffic arrives at the firewall, the Active Directory authentication table is searched for an entry corresponding to the source IP address of the traffic. If an entry exists, policies matching that entry are applied to the traffic and access is allowed or denied.
Table 1 lists Active Directory authentication table support by SRX Series devices:
Table 1: Active Directory Authentication Table Support by SRX Series Devices
SRX Series Devices | Active Directory Authentication Table Entries | Domains | Active Directory Controllers |
|---|---|---|---|
SRX100, SRX110, SRX210, SRX220 | 500 | 1 | 5 |
SRX240 | 1000 | 1 | 5 |
SRX550, SRX650 | 5000 | 2 | 10 |
SRX1400 | 20,000 | 2 | 10 |
SRX3000 line | 50,000 | 2 | 10 |
SRX5000 line | 100,000 | 2 | 10 |
Once the maximum number of authentication table entries is reached, no additional entries are created.
To be compliant with the Active Directory authentication table, entries must adhere to the following parameters:
- Usernames are limited to 64 characters.
- Group names are limited to 64 characters.
- Each entry can be associated with up to 200 relevant groups (configured in the source identity field). For example, if you belong to 1000 groups in LDAP and out of these, no more than 200 groups are configured in the source identity field, you are compliant with the Active Directory authentication table.
The Active Directory Authentication table must be enabled as the authentication source for integrated user firewall information retrieval.
 | Note: The priority option specifies the sequence in which user information tables are checked. Using the lowest setting for the Active Directory authentication source specifies the highest priority, meaning that the Active Directory authentication source is searched first. |
State Information for Active Directory Authentication Table Entries
Active Directory authentication table entries can be in one of four states:
Initial | — | Specifies that IP address-to-user mapping information was obtained by reading domain controller event logs and an entry was added to the authentication table. Entries in this state are changed to valid when the table is pushed from the Routing Engine to the Packet Forwarding Engine. |
Valid | — | Specifies that a valid entry was obtained by reading domain controller event logs or that a valid response was received from a domain PC probe and the user is a valid domain user. |
Invalid | — | Specifies that an invalid response was received from a domain PC probe and the user is an invalid domain user. |
Pending | — | Specifies that a probe event generated an entry in the authentication table, but no probe response has been received from the domain PC. If a probe response is not received within 90 seconds, the entry is deleted from the table. For a list of probe responses, see Understanding Integrated User Firewall Domain PC Probing . |
To display Active Directory authentication entries, along with their state information, use the following command:
Domain: www.example1.net Total count: 2 Source IP Username Groups State 192.168.10.2 u2 r1, r3, r4 initial 192.168.10.3 u3 r5, r6, r4 pending Domain: www.example2.net Total count: 2 Source IP Username Groups State 10.1.1.2 u4 r1, r3, r4 valid 10.1.1.3 u5 r5, r6, r4 invalid
Command options allow you to display information by user or group, and to define additional output levels—brief, domain, extensive, node.
Active Directory Authentication Table Management
Windows domain environments are constantly changing as users log in and out of the network and as network administrators modify user group information. The integrated user firewall feature manages changes in the Windows domain by periodically reading domain controller event logs and querying the LDAP server for user-to-group mapping information. That information is used in updating the Active Directory authentication table as appropriate.
Additionally, a probe function is provided to address changes that occur between reading event logs, or to address the case where event log information is lost. An on-demand probe is triggered when client traffic arrives at the firewall but a source IP address for that client cannot be found in the table. And at any point, manual probing is available to probe a specific IP address.
Changes to the active Directory Authentication table also occur due to source identity changes in the security policy configuration.
Table 2 describes events that trigger an Active Directory authentication table update.
Table 2: Events Triggering Active Directory Authentication Table Updates
Event | Active Directory Authentication Table Update |
|---|---|
A domain controller event log is read at configured intervals. | New IP address-to-user entries are added in the authentication table in initial state. Group information is retrieved from the LDAP server. When the authentication entry is pushed to Packet Forwarding Engine, the state is changed to valid. |
An on-demand or manual probe is sent to a domain PC. | An entry is added in the authentication table in pending state. If a probe response is not returned within 90 seconds, the state of the entry is deleted. |
An on-demand or manual probe response is received from a domain PC. | Based on the response, entries in pending state are changed to valid or invalid. For valid responses, the group information is retrieved from the LDAP server. For invalid responses, the entry is marked as invalid. |
An LDAP server query identifies new user-to-group mapping information. | Entries are updated with the group information. |
An LDAP server query identifies deleted user information. | Entries associated with that user are deleted from the table. |
An LDAP server query identifies deleted group information. | The affected group information is updated. For example, user2 belongs to group2, and group2 belongs to group1. And, group1 is listed as a source-identity for group2. For any authentication entry of user2, group1 is listed in its relevant groups. However, if group2 is removed from the LDAP server, user2 loses the connection with group1, and as a result, group1 is removed from the user2 authentication table. |
An LDAP server query identifies added group information. | If the group is referenced in a security policy, entries associated with this group are updated to add the group information. |
The source identity information is removed from a security policy configuration. | Entries associated with the source identity are deleted from Active Directory authentication table. |
| Note: If an entry is deleted from the table, any sessions attached to that entry are also deleted. If an entry in the table is updated to add or remove group information, there is no impact to existing sessions for that entry. |
To manually delete an entry from the table, use the request services user-identification active-directory-access active-directory-authentication-table command. Options exist for deleting a specific IP address, domain, group, or user.
| Note: When you use the CLI to delete an active directory authentication entry, the system closes the related session and writes a session-close message to the log file. However, the session-close message does not contain the source identity information for the user, that is, the user and user group information. |
To clear the contents of the Active Directory authentication table, use the clear services user-identification active-directory access active-directory-authentication-table command.
Timeout Interval for Table Entries
When a user is no longer active, a timer is started for that user’s entry in the Active Directory authentication table. When time is up, the user’s entry is removed from the table. Entries in the table remain active as long as there are sessions associated with the entry.
To set the timeout value, use the following statement:
The default authentication-entry-timeout interval is 30 minutes. To disable timeouts, set the interval to 0.
| Note: We recommend that you disable timeouts when disabling on-demand probing in order to prevent someone from accessing the Internet without logging in again. |
To view timeout information for Active Directory authentication table entries, use the following command:
Domain: www.example1.net Total entries: 2 Source IP: 192.168.1.2 Username: u2 Groups: r1, r3, r4 State: initial Access start date: 2014-03-22 Access start time: 10:56:58 Age time: 20 min Source IP: 192.168.1.3 Username: u3 Groups: r5, r6, r4 State: pending Access start date: 2014-03-22 Access start time: 10:46:58 Age time: 10 min
This example shows that the timer has started for two entries—the entry for user u2 will time out in 20 minutes, while the entry for user u3 will time out in 10 minutes. When session traffic is associated with an entry, the age time value changes to “infinite.”
