What does ALPN stand for in TLS and what is its role?

• A. Application-Layer Protocol Negotiation; It negotiates the application protocol (e.g., h2).
• B. Authentication Layer Protocol Negotiation; It negotiates authentication.
• C. Application Layer Protocol Negotiation; It negotiates HTTP methods.
• D. API Layer Protocol Negotiation; It negotiates APIs.

Answer: (B)

ALPN stands for Application-Layer Protocol Negotiation, and its role is to pick the application-layer protocol to use over a TLS connection during the handshake. In practice, the client provides a list of protocols it supports (for example, HTTP/2, HTTP/1.1, or other protocols), and the server selects one from that list, signaling its choice in the TLS handshake. This lets the client and server agree on the exact protocol to run over the secure channel without extra round trips or separate negotiation steps after the connection is established. It’s focused on choosing the protocol at the application layer, not on authentication, HTTP methods, or APIs.