According to network trace captured on NetScaler, there is no response from radius server after NetScaler sending Access-Request packet to radius server.
This issue occurred suddenly, and the related configuration of radius authentication on NetScaler has not changed.

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Update the certificate on radius server.

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Problem Cause

The certificate installed on radius server is expired, so radius server will not give response to NetScaler.

No response from radius server after NetScaler sending Access-Request packet to radius server.