Computer Networks
“The Internet is not just one thing; it’s a collection of things — of numerous interconnected networks.” — Bob Kahn
Overview
Computer Networks form the backbone of modern computing. Every web request, every email, every video stream relies on a layered stack of protocols working in concert. This section covers everything you need for placement interviews — from the OSI model to modern protocols like HTTP/3 and QUIC.
Why Networks Matter for Placements
- Every company uses distributed systems; understanding networks is non-negotiable
- FAANG interviews frequently test TCP/IP, DNS, HTTP, and security concepts
- System Design interviews assume strong networking fundamentals
- Real-world debugging requires understanding packet flow, latency, and failures
Section Map
graph TD
A[Computer Networks] --> B[OSI Model]
A --> C[TCP/IP Suite]
A --> D[TCP Protocol]
A --> E[UDP Protocol]
A --> F[DNS]
A --> G[HTTP & Web Protocols]
B --> B1[Physical Layer]
B --> B2[Data Link Layer]
B --> B3[Network Layer]
B --> B4[Transport Layer]
B --> B5[Session Layer]
B --> B6[Presentation Layer]
B --> B7[Application Layer]
C --> C1[IPv4 & IPv6]
C --> C2[Subnetting & CIDR]
C --> C3[NAT, ICMP, ARP]
C --> C4[DHCP]
D --> D1[Header & States]
D --> D2[3-Way & 4-Way Handshake]
D --> D3[Flow & Congestion Control]
D --> D4[TCP Variants]
E --> E1[UDP Header]
E --> E2[TCP vs UDP]
E --> E3[Applications]
F --> F1[Resolution Process]
F --> F2[Record Types]
F --> F3[DNS Security]
G --> G1[HTTP/1.1, HTTP/2, HTTP/3]
G --> G2[HTTPS & TLS]
G --> G3[WebSocket, REST, gRPC]
style A fill:#e1f5fe
style B fill:#fff3e0
style C fill:#e8f5e9
style D fill:#fce4ec
style E fill:#f3e5f5
style F fill:#fffde7
style G fill:#e0f2f1
How to Use This Section
- Start with OSI Model — understand the layered architecture
- Move to TCP/IP — the real-world implementation
- Deep dive into TCP — the most interview-heavy protocol
- Compare with UDP — understand trade-offs
- Study DNS — critical for system design
- Master HTTP — modern web protocols and APIs
Key Concepts Checklist
| Concept | Importance | Interview Frequency |
|---|---|---|
| OSI Model | ⭐⭐⭐⭐⭐ | Very High |
| TCP 3-Way Handshake | ⭐⭐⭐⭐⭐ | Very High |
| TCP vs UDP | ⭐⭐⭐⭐⭐ | Very High |
| DNS Resolution | ⭐⭐⭐⭐⭐ | High |
| HTTP/2 vs HTTP/1.1 | ⭐⭐⭐⭐ | High |
| Congestion Control | ⭐⭐⭐⭐ | Medium-High |
| Subnetting/CIDR | ⭐⭐⭐⭐ | Medium-High |
| HTTPS/TLS | ⭐⭐⭐⭐ | High |
| NAT & DHCP | ⭐⭐⭐ | Medium |
| QUIC & HTTP/3 | ⭐⭐⭐ | Growing |
Quick Reference: The Protocol Stack
Application Layer → HTTP, FTP, SMTP, DNS, SSH, HTTPS
Transport Layer → TCP, UDP, SCTP
Network Layer → IP, ICMP, ARP, OSPF, BGP
Data Link Layer → Ethernet, Wi-Fi (802.11), PPP
Physical Layer → Cables, Radio, Fiber, Electrical Signals
Cross-References
- For Operating System concepts related to networking (sockets, I/O), see OS Section
- For System Design applications, see System Design Section
- For Database networking (connections, replication), see DBMS Section