Chapter 2: The OSI Model and TCP/IP Model
Interview Questions
- Q1. Name the seven OSI layers and the PDU at layers 2, 3 and 4.
- Physical, Data Link, Network, Transport, Session, Presentation, Application. PDUs: frame (L2), packet (L3), segment/datagram (L4).
- Q2. Explain the TCP three-way handshake.
- Client sends SYN, server replies SYN-ACK, client sends ACK. After this the connection is established and data can flow with sequence numbers and acknowledgements.
- Q3. What is the difference between TCP and UDP? Give an example of each.
- TCP is connection-oriented and reliable (HTTP, SSH, MySQL). UDP is connectionless and faster with no delivery guarantee (DNS, VoIP, video streaming).
- Q4. At which layer do an AWS Application Load Balancer and a Network Load Balancer operate?
- ALB works at Layer 7 (routes by host/path/headers). NLB works at Layer 4 (TCP/UDP, ports).
- Q5. What happens when you type a URL in the browser?
- URL parsing → DNS resolution → TCP handshake → TLS handshake → HTTP request → server/app/database processing → HTTP response → browser renders HTML/CSS/JS.
- Q6. What is encapsulation?
- Each layer adds its own header (and Layer 2 also a trailer) around the data from the layer above before passing it down; the receiver removes them in reverse order (decapsulation).