You have configured ACS to perform machine authentication against Active Directory.
Both ACS and Active Directory hosts can ping each other, there is no firewall between them, and ACS trusts the correct CA.
Yet the clients that are performing machine authentication with EAP-TLS and using valid certificates are failing to authenticate.
What might the reason be?
The issue described in the question indicates that the configuration for machine authentication with EAP-TLS on ACS is not working as expected, despite successful communication between ACS and Active Directory hosts. To identify the possible reasons for this issue, let's examine each answer option in detail:
A. The wrong UDP port for Active Directory is configured on ACS. This option refers to a possible misconfiguration of the network port used by Active Directory for communication. However, since ACS and Active Directory hosts can successfully ping each other, it is unlikely that a wrong port is causing the authentication failure. Therefore, this option is not the correct answer.
B. Machine access restrictions are enabled on ACS. This option refers to a possible restriction or policy set on ACS that is preventing machine authentication. It could be that the machine access policies are not allowing the specific clients to authenticate successfully. Therefore, it is a valid option to consider.
C. The client certificate key is less than 2048 bit. This option refers to the possibility that the client certificates used for authentication do not meet the minimum security requirements for EAP-TLS authentication. Typically, EAP-TLS requires a minimum key size of 2048 bits. Therefore, if the client certificates have keys that are less than 2048 bits, authentication will fail. This option is a valid consideration.
D. The wrong date and time are on the ACS server. This option refers to a possible issue with the time and date settings on the ACS server. If the server's time and date are incorrect, it can cause authentication to fail. However, this option is unlikely to be the cause of the issue if only machine authentication is failing while other forms of authentication are working correctly.
E. The host is not configured in the ACS internal database. This option refers to the possibility that the client host attempting to authenticate is not configured in the ACS internal database. If the host is not configured, then authentication will fail. Therefore, this option is a valid consideration.
In summary, option B, C, and E are all valid considerations for the machine authentication failure. However, further troubleshooting would be required to determine the exact cause of the issue.