Symptom
The Firepower Management Center (FMC) using Radius as the external authentication method only allows the shared secret key length to be 30 characters or less after upgrading the FMC to version 7.4.0 or 7.4.1. This limitation results in external authentication failures without providing an error during the shared secret key configuration.
Conditions
The issue occurs when the FMC is running version 7.4.0 or 7.4.1 and an external authentication method with a RADIUS shared secret key exceeding 30 characters is configured. Authentication works as expected in earlier versions.
Workaround
To avoid the issue, reduce the RADIUS shared secret key length to a maximum of 30 characters.
Further Problem Description
The lack of an error message during the shared secret key configuration can lead to confusion for administrators, as they may not be aware of the character limit until authentication fails.
