How does the SSL proxy service identify SSL traffic?

The correct answer is B. by using AppID results. Junos SSL proxy does not identify SSL/TLS sessions by assuming that encrypted traffic always uses TCP/443. That would be technically weak because SSL/TLS can run on nonstandard ports, and non-SSL applications can also use common HTTPS ports. Juniper’s SSL proxy documentation explains that SSL proxy works with application security services and that AppID is used in the encrypted-traffic inspection workflow. In earlier wording from Juniper AppSecure material, SSL proxy uses application identification services to determine whether a session is SSL encrypted; in current Junos documentation, SSL proxy and AppID are tightly linked so encrypted sessions can be identified, decrypted, inspected, and then re-encrypted for enforcement.

Option A is wrong because the URL is inside the HTTP payload, and in HTTPS much of the meaningful HTTP content is encrypted before SSL proxy inspection occurs. Option C is wrong because destination port is only a rough hint, not a reliable detection method. Option D is wrong because certificates are used in the SSL/TLS handshake and proxy trust model, but the service’s traffic classification relies on AppID results, not merely reading the server certificate. Reference topics: SSL Proxy, AppID, encrypted session detection, SSL/TLS inspection, application security services.