Enable external authentication servers and fallback options

Last published : Sep 21, 2026
Fallback option enables local authentication to take over if the external server authentication fails. A user configured on both NetScaler® ADM and external authentication server can log on to NetScaler ADM, even if the configured external authentication servers are down or not reachable. To ensure fallback authentication work:
  • Non-nsroot users must be able to access NetScaler ADM if external server is down or not reachable
  • You must add at least one external server
NetScaler ADM also supports a unified system of authentication, authorization, and accounting (AAA) protocols (LDAP, RADIUS, and TACACS), along with local authentication. This unified support provides a common interface to authenticate and authorize all users and external AAA clients accessing the system.
NetScaler ADM can authenticate users regardless of the actual protocols they to communicate with the system. Cascading external authentication servers provides a continuous non-failing process for authenticating and authorizing external users. If authentication fails on the first authentication server, NetScaler ADM attempts to authenticate the user by using the second external authentication server, and so on. To enable cascade authentication, you must add the external authentication servers in NetScaler ADM. You can add any type of the supported external authentication servers (RADIUS, LDAP, and TACACS).
For example, consider that you want to add four external authentication servers and configured two RADIUS servers, one LDAP server, and one TACACS server. NetScaler ADM attempts to authenticate with the external servers, based on the configurations. In this example scenario, NetScaler ADM attempts to:
  • Connect with the first RADIUS server
  • Connect with the second RADIUS server, if the authentication has failed with first RADIUS server
  • Connect with the LDAP server, if the authentication has failed with both RADIUS servers
  • Connect with the TACACS server, if the authentication has failed with both RADIUS servers and LDAP server.
Note
You can configure up to 32 external authentication servers in NetScaler ADM.
Related information

Configure fallback and cascade external servers

  1. Navigate to Settings > Authentication.
  2. On the Authentication page, click Settings
  3. On the Authentication Configuration page, select EXTERNAL from the Server Type list (only external servers can be cascaded).
  4. Click Insert, and on the External Servers page, select one or multiple authentication servers to cascade.
  5. Select the Enable fallback local authentication check box if you want the local authentication to take over if the external authentication fails.
  6. Select the Log external group information check box if you want to capture the external user group information in the system audit log.
  7. Click OK to close the page.
    The selected servers are displayed under External Servers:
    External servers
You can also specify the order of authentication by using the icon next to the server names to move servers up or down the list.