Which authentication uses a separate communication channel to deliver the OTP or PIN?

• A. In-Band Authentication
• B. TACACS+
• C. RADIUS
• D. Out-of-Band Authentication

Answer: (D)

Out-of-band authentication relies on delivering the one-time password or PIN through a channel separate from the one used to initiate the login. For example, you might enter your username on a web page, and the system sends an OTP via SMS to your phone or via a hardware token or voice call. This separate path makes it harder for an attacker who is capturing traffic on the primary channel to obtain the OTP, increasing security.

In-band authentication, by contrast, delivers the OTP through the same channel used for the login request—for instance, within the same web page or app session.

TACACS+ and RADIUS are authentication protocols that manage credentials and access control, not specifically about delivering OTPs via a separate channel, so they don’t fit the concept described.