Application Layer Services and Protocols Questions

Evaluate understanding of how application layer services use the network and how failures at this layer differ from lower layer problems. Topics include the Hypertext Transfer Protocol and Hypertext Transfer Protocol Secure, fundamentals of the Transport Layer Security handshake and certificate validation, how load balancers and proxies affect connection termination and header handling, and interactions between protocol versions and performance. Candidates should also explain the Domain Name System resolution path including caching and recursion, and the basics of Simple Mail Transfer Protocol and common email delivery and relay failure modes. Interviewers may probe how to distinguish transport level retransmission or connection issues from application level errors, how to interpret response status codes and error messages, and how to diagnose application failures that occur despite apparently healthy lower layer connectivity.